Noisy chromatograms, random spikes, and poor detector sensitivity are symptoms of a dirty FID — a common problem in gas chromatography. You will consistently obtain better chromatograms and reduce instrument downtime if you keep the FID clean.

The most common source of contamination in a flame ionization detector (FID) is bleed from silicone stationary phases and silylating reagents, which combust in the FID and produce silica. When deposited on surfaces within the detector, this white powder causes noisy chromatograms, random spikes, and poor detector sensitivity Figure below;

Figure 1. A Noisy Chromatogram, Caused by a Dirty FID

In this article we will

1. methods of troubleshooting noise to confirm whether the source is a dirty FID,
2. method of cleaning FIDs, and
3. ways to reduce contamination in the future
   IS THE DETECTOR REALLY THE PROBLEM?
   Before you shut down your instrument and clean your detector, it is wise to confirm that the problem is detector-related, rather than related to some other component of your system. The few, simple procedures described here can eliminate other possibilities as the source of the problem.

• Carrier Gas and Stationary Phase

Seal the detector inlet in the oven with a  plug and ignite the detector. If the chromatogram noise disappears, then the source of the problem is contaminants in the carrier gas or bleed from the chromatography column, not a dirty FID.

• Hydrogen and Air Systems

Hydrogen and air used in the sulfide can be a source of contamination, especially when problems emerged after replacing the cylinder. An incorrect flow rate in either source can cause noise, lack of sensitivity, and/or difficulty when igniting the flame. A contaminated cylinder of gas could be the source of the problem, especially if the noise appeared several hours after you changed a cylinder. Check each cylinder for contaminants and replace if necessary. To eliminate the problem of contaminated air, we recommend using a zero air generator

• Electrical System

Electrical interference may exhibit similar symptoms dirty FID. There may be a defect electrometer, poor contact or interference by other devices in the lab. To isolate this source of noise, disconnect the electrometer cable(s) from the FID. If noise persists, it is coming from the electrical system.

Precautions before cleaning

• Isolate electrical source, make sure to unplug the power cord!
• Remember that the detector may be hot! be sure the collector assembly is cool before you begin
• When dismantling FIDU pay attention insulating parts. Use tweezers, whether these parts do not transfer dirt from your hands or gloves. Beware of possible scratches.
• Pay Attention ! Carefully note the distance from the collector assembly to the flame jet.

How to Clean an FID
To properly clean an FID, you must clean the
1. Collector assembly
2. The jets:
Jet cleaning  procedure.

• Run a cleaning wire through the top of the jet. Run it back and forth a few times until it moves smoothly. Be careful not to scratch the jet. (Do not force too large a wire or probe into the jet opening or the opening will become distorted. A loss of sensitivity, poor peak shape and/or lighting difficulties may result if the opening is deformed.)
• Fill an ultrasonic cleaning bath with aqueous detergent, and place the jet in the bath. Sonicate for five minutes.
• Use a jet reamer to clean the inside of the jet.
• Sonicate again for five minutes.
  NOTE: From this point on, handle the parts only with forceps!
• Remove the jet from the bath and rinse it thoroughly, first with hot tap water and then with a small amount of GC-grade methanol.
• Blow the jet dry with a burst of the compressed air or nitrogen, and then place the jet on a paper towel and allow it to air dry.

3. The Teflon® or ceramic insulators: Ceramic parts of an FID are best cleaned with aqua regia, a 1:~3 mixture of concentrated nitric and hydrochloric acids, at ambient or mildly elevated temperature. Before treatment, remove all metal and rubber from the ceramic parts – aqua regia will attack these.
4. The housing.

After you have cleaned all parts of the detector, check all Orings and replace them if necessary. Worn-out O-rings will cause gas leaks, which can produce detector noise or an increase in detector contamination. Reassemble the FID, light the flame, and allow the detector temperature to equilibrate at 10°C–50°C higher than the column will reach during typical operation. This will reduce the amount of phase condensing onto the detector parts. Do not exceed the maximum temperature limit of the stationary phase – many columns fit far enough into the detector to expose the phase to these elevated temperatures. Set the proper flow rates for hydrogen and compressed air (refer to the instrument manual), and ignite the flame. Turn on the electrometer and allow a few minutes for warmup. The flame should now be stable and noise-free.

REDUCING DETECTOR NOISE AND CONTAMINATION

1. Conditioning:
   Most detector noise and contamination is the result of column bleed. The amount of bleed is greatest when the column is initially conditioned. Your detector will remain clean longer if you condition a new column before connecting it to the detector. Byproducts eluted during conditioning, potentially harmful to the FID, are voided into the oven. Connect the column inlet to the injector as usual. Place a restrictor at the column exit to prevent back diffusion of air into the column (exposure of a heated column to air can destroy the liquid phase). Purge the column with carrier gas at room temperature for a few hours before you begin the temperature program. Do not allow a combustible carrier gas such as hydrogen, methane, etc. to exit the column into the oven. Pipe these materials out of the oven and into a hood. (Be sure to attach a restrictor to the outlet of the pipeline in the hood.) Consult the column manufacturer for conditioning details, i.e., duration and temperature of conditioning. Do not routinely condition new columns at the maximum temperature limit of the stationary phase – this will reduce column life. Connecting a well-conditioned column to a clean FID should produce good sensitivity. If detector stability quickly degenerates, you should evaluate the quality of your stationary phase and carrier gas.
2. Stationary Phase
   Use GC quality stationary phases whenever possible — they are purified to remove lower molecular weight components. Technical grade materials will bleed more than GC quality materials.
3. Carrier Gas
   Moisture and oxygen in the carrier gas will cause stationary phase to deteriorate and bleed. Use chromatography-quality gases, and periodically monitor the gas system for leaks, which might allow atmospheric oxygen and water to enter the column.
4. Septa
   Frequently check the septum for leaks. A leaking septum can allow oxygen and water to enter the carrier gas and cause the stationary phase to deteriorate and bleed. To check for leaks without contaminating the septum (and subsequent samples) with liquid leak detectors, use an electronic GOW-MAC leak detector, If you run your instrument frequently, we recommend you change the septum regularly.

   Reference
   https://www.agilent.com/en/support/gas-chromatography/kb001441https://www.chromservis.eu/i/32606/g/hints-and-tips
   https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Supelco/Bulletin/4488.pdf
   http://hiq.linde-gas.com/en/analytical_methods/gas_chromatography/flame_ionisation_detector.html

Written by Oweh Gabriel,

www.aasnig.com, gabriel@aasnig.com

08035696303

 

 

 

 

 

BY: Douglas E. Raynie

Over the past several years, there has been a trend toward preparing increasingly smaller samples. In many cases, this approach was taken to demonstrate that extractions and sample handling procedures at the microscale and smaller is possible. With the current emphasis on bioanalytical and related technologies, even greater legitimacy is given to these approaches. Hence, the advent of dried-blood spot (DBS) analyses and other approaches. One approach to microsampling for bioanalyis is solid-phase microextraction (SPME), also referred to as bio-SPME, which is discussed here.

Sampling and Sample Heterogeneity

My thoughts as I heard of recent, somewhat controversial, developments in finger-prick sampling for blood tests were concern over the statistics of sample size and homogeneity. Most analysts are widely aware that the standard deviation of sampling and analysis increases with decreasing analyte concentration. Horwitz (1) evaluated interlaboratory validation studies and developed the “trumpet” shown in Figure 1. Although some bias is evident in every sampling protocol, when Meyer (2) presented the relationship between sampling and measurement uncertainty in 2002, she claimed that deviations from the Horwitz curve were caused by the sample matrix and the sample preparation procedure. Meyer provided the following advice: Avoid all possible sources of contamination with trace analysis; use large volumes when possible since smaller volumes are difficult to handle and loss of sample material is less severe; mass-based measurements are often more reproducible than volumetric measurements; and use minimal sample handling steps with small-volume samples. Others have also demonstrated the relationship between sampling precision and sampling size. For example, Thiex and colleagues (3) reported the expected relative standard deviation from laboratory subsampling as a function of maximum particle size within the sample. As presented in Table I and substantiated by the Horwitz relationship, one cannot simultaneously have good sampling precision and small samples.

Figure 1: The Horwitz “trumpet” displaying the inverse relationship between analyte concentration and relative standard deviation of sampling. (Adapted from reference 2.)

Moving beyond sample homogeneity concerns, the Royal Society of Chemistry’s Analytical Methods Committee explored representative sampling from an analytical and statistical viewpoint (4). They prefer the term “appropriate sampling” to “representative sampling.” They made this distinction because of the survey statistics definition of representative sampleas “a sample for which the observed values have the same distribution as that in the population,” while the analytical definition states “a sample resulting from a sampling plan that can be expected to reflect adequately the properties of interest in the parent population.” This concept of adequacy in the analytical definition implies an inherent sampling bias and recognizes that in many, especially regulatory, cases analytical results are compared with a limit value. This limit value is often a “fitness for purpose,” which allows the use of analytical results to be used in decision making. Appropriateness of sampling can be improved by increasing the sample size or the number of samples.

Note that these relationships between sample size and heterogeneity are primarily derived from investigations of solid samples, including food and feeds. However, most microsampling applications are used in bioanalysis, especially those involving blood samples. For reasons of diffusion and turbulent flow, liquid samples can be assumed to be considerably more homogeneous than solid samples.

Overview of Microsampling in Bioanalysis, Including Bio-SPME

Along with analysis of DBS, paper-based and more-conventional microfluidic approaches are gaining popularity. Such procedures are simple, inexpensive, and easy to use. A balance of hydrophobic and hydrophilic treatments controls fluid movement in these devices, resulting in their claimed reliability. One significant advantage of these approaches is their applicability outside of the laboratory, including nonclinical settings, though sample drying of blood spots can present a concern. Capillary microsampling allows collection of microliter sample volumes along with subsequent steps such as separating plasma and serum. These approaches will be the subject of a future “Sample Prep Perspectives” column.

Another sample preparation trend we’ve noticed is interest in SPME, especially since the lapse of patent protection of the initial products. In the case of conventional SPME, a stationary phase, usually a gas chromatography (GC)-type phase, is coated onto a fused-silica fiber encased in a syringe-needle device. The coated fiber is exposed to the sample by either immersion in a liquid sample or exposure to a vapor sample. The adsorbed sample is then desorbed either thermally in a GC inlet or via solvent rinsing into a liquid chromatograph.

Biocompatible SPME (bio-SPME) is a microsampling approach for bioanalysis based on SPME, but featuring some key differences. With bio-SPME, functionalized silica particles are embedded in an inert binder that is coated or bonded onto metal fibers. The use of the binder minimizes interferences from biomacromolecules. Bio-SPME is available in hypodermic needle and pipette tip formats. Like conventional SPME, the approach is not exhaustive and relies on an equilibrium between the analyte in the biofluid and the fiber materials. Figure 2 displays the kinetics of bio-SPME sampling, which are similar to conventional SPME. Initially, a rapid adsorption of the analyte onto the functionalized silica is observed, followed by an asymptotic approach to the equilibrium amount of analyte isolated.

Figure 2: The kinetics of the bio-SPME process, demonstrating an asymptotic approach to quantitative equilibrium. (Courtesy of Supelco.)

Two particular advantages of bio-SPME are of special interest. First, the device can be directly inserted into small animals for sampling at or near the point of interaction during physiological studies. This allows multiple analyses per animal, since the animal is not sacrificed, leading to more cost-effective studies and more reliable results since there are multiple analyses per animal. Relative standard deviations around 30% demonstrate the need to strongly consider the uncertainty considerations presented by Horwitz and discussed earlier. The second major advantage is the direct ionization of analytes on the bio-SPME fibers for mass spectrometry, as demonstrated in Figure 3 (5). This schematic shows the ionization occurring when the fiber and spray tip are sharp and a spray solvent carries the analyte into a high-voltage region to create an electric field between the bio-SPME device and the inlet to the mass spectrometer. Quantitative results are similar to other reports of bio-SPME and are 5–10x better than with DBS analysis. Spray solvent flow rates, positioning of the fiber, and other parameters are being optimized.

Conclusions

Microsampling for bioanalysis and other applications is gaining in popularity. One new technique in this area is the reapplication of the SPME approach, designed for biological applications. However, in all microsampling approaches, measurement uncertainty and sample homogeneity concerns must always be considered.

References

1. W. Horwitz, L.R. Kamps, and K.W. Boyer, J. Assoc. Off. Anal. Chem. 63,1344–1354 (1980).
2. V. Meyer, LCGC North Am. 20(2), 106–112 (2002).
3. N. Thiex, L. Novotny, C. Ramsey, G. Latimer, L. Torma, and R. Beine, Guidelines for Preparing Laboratory Samples (Association of American Feed Association Officials, 2008).
4. M.H. Ramsey and B. Barnes, Anal. Methods 8, 4783–4784 (2016).
5. S. Ahmad, M. Tucker, N. Spooner, D. Murnane, and U. Gerhard, Anal. Chem. 87, 754–759 (2015).

Written by Akinbuli Opeyemi,

www.aasnig.com, opeyemi@aasnig.com

07084594004, 08068129603

Introduction
Regular replacement of crucial parts can help keep your HPLC systems at optimum performance, reduce system downtime and repair costs, as well as extend your instrument’s life time. However, these benefits can only be achieved when using high-quality parts that are durable, clean, and fit perfectly into the system. We inspected different LC instrument spare parts from Agilent and other vendors.
The results show deficiencies in parts from other vendors, including:
• Inconsistent materials
• Contamination issues
• Shorter life time
• Outdated design
Therefore, use of parts not from Agilent could cause premature instrument failure, increase downtime, and deliver inaccurate or false results.

Solvent inlet filters
Solvent inlet filters represent the first barrier for retaining particulates, precipitation, microbes from mobile phases,
buffers, and salt solutions. Filters are significant in preventing system blockage, pressure increase, and contamination.

Cleanliness
Cleanliness of parts is vital for avoiding system contamination. Agilent solvent filters are packed in ultraclean antistatic bags with an inner metallic coating that does not release contaminants such as plasticizers or antioxidants.
LC/MS analysis shows that filters not from Agilent, packed in normal plastic packs, can cause extra peaks during analysis. Erucamide, a common slip agent used in polyethylene films, is one such example.

Pore size
A good solvent glass filter should have a defined, homogenous pore size to effectively block particulates above a certain size, while letting mobile phases through without significant pressure increase. Too large pore size leads to deficiency of filtration, while pores that are too small can cause pressure increase, resulting in solvent pumping difficulties. Inspection of Agilent and other vendor solvent glass filters by scanning electron microscopy (SEM) shows uniform pore sizes and smooth particle surfaces in the Agilent filter. In contrast, other vendor filters had inconsistent particle and pore sizes. The small particles or particle fragments shown on the other vendor filter could be flushed into the flow path, blocking the pump frit, capillaries, valves,
or columns.

PTFE frits
The PTFE frit is another crucial part in the flow path that prevents particulates and microbes from getting into the system. It is important that frits maintain their shape up to the pressure limit of the system, since collapse or abrasion of the frit can release PTFE particles, resulting in blockage or loss of analysis efficiency. SEM inspection reveals. If the frit is abraded,particles that are too large can block the flow path, while
particles too small can pass through the column inlet frit, getting into the column, or even reach the detector causing
contamination of the flow cell. In contrast to alternative frits, Agilent frits are designed to have a defined particle size to avoid these issues.

Pump piston seals
The piston seal is an essential part of the pump that directly impacts its performance, which depends on many design
characteristics.

Spring tightness
Seal springs have to apply a constant force that complies with the tolerances of the instrument. Springs that are too soft can cause diffusion of air bubbles into the pump head, resulting in pressure ripple and air in the column. Springs too hard can lead to more abrasion between seal and piston, leading to significant decrease in the seal’s lifetime. Agilent seals use specially designed springs that maintain optimal strength to ensure perfect sealability and longevity. Comparison with third-party seals clearly shows differences in size, space, and density of the spring coils.

Material
Agilent seals are manufactured from a proprietary polymer blend with optimized elasticity, firmness, and hydrophobicity, which have large effects on pressure ripple, cold-flow behavior of solvents, and removal of air bubbles. Agilent seals also feature optimal functionality at a wide temperature range from 4 to 60 °C, to adapt to different temperature conditions in different regions. Another feature is that we use specific copper-free manufacturing tools instead of common brass tools, to avoid copper contamination of the system. Therefore, use of third-party seals that clearly have different designs, materials, and features than Agilent seals can result in high risk of compromising your instrumental and analytical efficiency. Agilent uses an ultraclean plastic cap to protect the needle tip from collision and abrasion, contamination, and blockage through particulates. In comparison, there was no proper protection on the third-party needle.

Outlet check valves
The outlet check valve has profound impact on pressure stability and pump flow. The valve has to work quickly,
accurately, and reliably to achieve a precision eluent flow without disturbance such as pressure drop or pressure ripple.The original design of the Agilent outlet check valve had a cylindrical seat and separate gold seal. The cylindrical seat was limited in its resistance to high pressure and alternating pressure loads, resulting in limited life time. In addition, the separate gold seal cap could be deformed by pressure loads due to the ductility of gold, causing leakage so that cap had to be retightened and sometimes changed.
Agilent therefore developed a new design for its outlet check valve to enhance durability and reliability. The new generation outlet valve has a unique double-coned seat to resist the highest pressure ranges, as well as an integrated gold‑plated seal to minimize tolerance of seal edge geometry. In addition, since a gold seal cap is no longer required, there is no need to change the gold seal, which makes this part maintenance free. In comparison, the outlet check valve from another vendor still uses the older design, resulting in risks of higher pressure ripple, poorer flow and retention time precision, as well as shorter life time and more maintenance.

Injection needles and needle seats.

The injection needle and needle seat need to match perfectly to minimize sample carryover and ensure a leak‑free flow path. Comparison of Agilent and third-party needle seat assemblies shows large differences in design. While the
other vendor still uses the older design, Agilent introduced a design in 2011 with more robust material, improved
performance, higher reliability, and larger pH range (0 to 13). The conical geometry at the center of the needle
seat also reduces sample dispersion. In addition, Agilent needles and needle seats are thoroughly tested to guarantee
full functionality for more than 30,000 injections.

Lifetime
Agilent rotors are rigorously tested and guaranteed for at least 30,000 injections. After 30,000 switch cycles, the Agilent rotor surface still seemed flat and consistent, and the contacting stator surface appeared clean. In
contrast, the third-party rotor already showed severe surface damage and a contaminated stator surface after 26,000
switch cycles. Therefore, shorter lifetime and potential carryover and leakage are expected when using
third-party seals. Photomicrographs showing the superior smoothness and integrity of the surface of an Agilent rotor seal.

Rotors
The rotor is a highly stressed part of the autosampler that is constantly switched back and forth, sliding over the stator. Its durability and life time is governed largely by the material and surface finish. Comparison of Agilent and third-party rotor seals revealed major differences in these aspects.

Surface smoothness
Microscopic inspection (Figure 9) shows the consistent flat surface of Agilent rotor seals, while scratches, flecks, and a jagged hole edge are clearly evident on the third-party rotor seal. The flecks indicate inconsistent material composition, and the scratches and jagged edge can definitely affect the sealing of the rotor to the stator, resulting in leakage or increased sample carryover.

Packaging
Scratches and flatness of rotor seal surfaces can also resultfrom poor packaging. Agilent rotor seals are packed in shapestable plastic boxes to avoid surface damage and deformation of the seal during storage and transportation, while third-party rotor seals are packed in normal plastic bags without special protection.

Reference
© Agilent Technologies, Inc., 2015
www.agilent.com/en-us/services/analytical-instrument-services/repairmaintenance/crosslab-preventive-

written by Ayodeji Ogunlowo

ayodeji@aasnig.com

CONCLUDING PART

 Checking GC Connections

Checking all fittings for leaks immediately after installation, maintenance, and periodically while in use is an excellent practice. A handheld electronic detector capable of detecting a helium leak of 0.0005 mL/min in air is available commercially. Handheld leak detectors are particularly useful for finding leaks quickly either inside or outside the GC oven. It is good practice to always use a leak detector to check for leaks each time a column, fitting, or cylinder is changed. An excellent starting point for system troubleshooting is to first check for

potential leaks. Avoid using water soap solutions, as these can be drawn back into the GC flow path, severely impacting chromatographic results even to the point of causing permanent column damage.

Checking a GC/MS for Leaks

A vacuum or ion gauge, if ordered with your instrument, is useful for monitoring vacuum pressures under typical operating conditions in GC/MS. A vacuum gauge is very useful for isolating potential leaks to either the vacuum (MS) or pressurized (GC) side of the instrument. Vacuum readings in the 10–5 or 10–6 Torr range are typical for a system holding vacuum with a flow rate of 1.0 mL/min on a 30 m × 0.25 mm, 0.25 μm GC column. When the MSD is capped and pumped down, vacuum readings typically drop to the 10–6 or 10–7 Torr range in the absence of a leak. If the vacuum pump does not reach these levels relatively quickly, a leak somewhere in the MS is indicated. Make sure the purge vent is closed, the transfer line fitting is installed correctly, and that the large O-ring on the vacuum side plate is positioned correctly.

A software-based performance check of air and water is available in most GC/MS. This check looks at GC/MS ion traces of molecules typically found in air relative to ion 69 found in the calibrant. Ions 18 (water), 28 (N2), 32 (O2), 44 (CO2), and 69 (typical base peak from PFTBA used during auto-tune) are all monitored. Nitrogen (28) levels above 10% relative to the 69 peak indicate that the system has not had sufficient time to pump down or that there is an air leak. An air leak will typically show nitrogen:oxygen in a 4:1 ratio. Water (18) is also typically present, particularly after a system had been vented and exposed to ambient air. An equilibrated leak-free system should show nitrogen (28) well below 10% with oxygen 32 at approximately ¼ of the signal seen for nitrogen, and ideally water (18) lower than the N2 (28) peak.

Troubleshooting leaks in GC/MS is a process of elimination, looking at each site where a leak can occur. A fluorocarbon (for example, 1,1,1,2-tetrafluoroethane, ions 69 and 83) or argon (ion 40) spray can with a plastic tube to direct the flow is very useful in isolating a leak. A short spray at a suspect point and monitoring the appropriate ions in manual tune is a powerful tool for isolation. Key points to check are the transfer line connection in the oven, septum nut, column nut, and the large O-ring on the vacuum plate of the MS. Once a leak has been isolated the leak can be remedied by replacing a septum, resetting a column connection, or cleaning the O-ring on the vacuum plate, and reinstalling it back into the groove on the plate.

Innovations to Minimize Leaks

Figure 2 shows a total-ion chromatogram for an air and water check on a system that is operating normally. In this case, self-tightening column nuts were installed at the transfer line and inlet fittings. These column nuts provide a leak-free seal using a short polyimide/graphite ferrule at both column connections, without the need to retighten the fitting after more than 300 heat cycles. Use of these column nuts eliminates the need to retighten the inlet or mass spec transfer-line connections after oven heat cycling. Furthermore, because very low torque is needed to make a leak-free seal when using the self-tightening column nuts, these nuts are installed using only fingers, not wrenches, which eliminates the risk of over tightening and damage to the fittings (see Figure 3)

                                                                                                                                                                                               Figure 3. Agilent self-tightening column

     Figure 2. Example air and water check                                             nuts installed at the transfer line and inlet fittings.

Conclusions

By using tools, supplies and best practices that provide a leak-free GC or GC/MS, analysts can improve performance and productivity of their system. Agilent UltiMetal Plus Flexible Metal ferrules provide robust leak-free column connections, along with an inert surface for fittings in the sample flow path. The Agilent innovative self-tightening column nuts using standard short polyimide/graphite ferrules eliminate the need to retighten GC column fittings, including the mass spec transfer line, after repeated heat cycling. These new fittings also have the advantage of using only short polyimide/graphite ferrules for inlet, detector, and

mass-transfer-line connections. Following the best practices described in this technical overview and accessing the references below will help GC and GC/MS users identify potential air leaks, where to find them, and how to fix and prevent them quickly. One rule of thumb is to adjust fittings, septa, and O-ring seals to be JTE

for the best results

 CONCLUDED.

 References

Best Practice for Identifying Leaks in GC and GCMS:  Technical Note, Agilent Technologies

 

Written by Muyiwa Adebola

muyiwa@aasnig.com, www.aasnig.com

07084594001, 07084594004

Let’s first properly define carryover in the context that I’d like to discuss here. An injection is made and a chromatogram obtained. On injecting a “blank” as the next injection, one or more of the components of the previous injection appear in the “blank” chromatogram.

This definition needs further clarification:

1. Blank injection can be a pure solvent (or solvent mixture), or, if contamination of the solvent(s) is suspected, then the “blank” may be an injection of air (for example, a 0 mL injection).
2. While the “blank” may contain components of the previous injection, depending upon the solvent used, one may observe carryover from several injections previously. Here, I refer to the often puzzling issue where several injections are made without evidence of carryover then “out of the blue” a component will appear in the chromatogram that was present in a sample from several injections ago. I will explain this more fully subsequently.

In summary, carryover in this context is related to the instrument rather than solvent contamination. However, while the contamination may not arise from the sample solvent injected, the nature of the solvents used within the system are intrinsically linked to the majority of carryover problems in gas chromatography (GC). So, why is this and what can be done about it? To help with the visualization of the concepts discussed below, Figure 1 is a schematic of a typical split–splitless inlet with the various gas flows noted.

Injection Volume Related Carryover

In split–splitless injection, the injected liquid expands rapidly to form a gas plasma containing our analytes, hopefully also in the gas phase. The space within the inlet, into which this expansion occurs, is primarily dependent upon the internal volume of the inlet liner used, and the available volume may vary significantly depending upon the design of the liner used. Most manufacturers will publish the internal volume of their various liner styles or this information will be available through one of the many online vapour volume calculators: CHROMacademy Calculator (1), Agilent GC Calculator (2), and Restek Backflash Calculator (3).

The inlet pressure (determined by the total flow into the inlet), inlet temperature, and sample volume injected all influence the volume of gas created from the injected sample. If the volume of gas created by the sample exceeds the available volume within the liner, gas may overflow from the liner and will typically end up in the septum purge and carrier gas lines (yes, overflowing sample vapour may overcome the forward pressure of the inlet gas supply and flow back up the carrier gas inlet lines). As these lines are typically unheated, higher boiling and more polar sample components may condense and “coat” the lines. Any subsequent overloaded injection (typically known as “backflash”) may then flow through the unheated lines and re‑solubilize the condensed components. As the inlet pressure equalizes, or as the split line is opened in the case of splitless injection, then this re-dissolved component is drawn back into the inlet and may ultimately enter the column, therefore causing carryover.

One should note that this may not occur every time a backflash injection is made, and in some cases the polarity of the sample vapour relative to the condensed contaminant will determine how well the contaminant is re-dissolved, and therefore whether it is seen within the subsequent chromatogram. This can lead to the situation in which the contaminant may not become obvious until several injections later, if the solubility of the contaminant is not high in the intermediate injections. So, a polar contaminant may not appear in backflashed injections of, say, hexane, but may then become apparent when a backflashed injection of methanol is made several injections later. Not only is the problem of backflash rather insidious, it can also be very confusing because the appearance of the carryover may appear to be random and not apparent in the injections immediately following.

As splitless injections have inherently lower total gas pressure in the inlet (only the carrier flow is passing through the liner) and as the residence time of the sample solvent within the inlet is higher, splitless injection is considered to have a higher risk in terms of injection backflash and inlet contamination.

In order to overcome backflash issues there are three choices:

1. Use pressure pulsed injection—in which the inlet pressure (total flow into the inlet) is increased during the injection phase and then reset to the desired pressure (and column flow) post injection. In splitless injection the pressure pulse time is usually matched to the splitless time.
2. Reduce the amount injected
3. Use a small split to increase the inlet pressure during injection

Obviously choices 2 and 3 need to be evaluated against any loss in sensitivity unless the sample concentration can be increased prior to injection, whereas choice 1 will
not lead to any reduction in analytical sensitivity.

The calculators mentioned above can all be used to assess the likelihood of backflash within the inlet and therefore will help to mitigate the issue.

Contamination of the Split Line

You may have noted that the split line on your gas chromatography instrument is also unheated. So whatever issues occur with the deposition of components into the carrier and septum purge lines may also occur within the split line. However, most inlet designs have a split line lower within the inlet than the split line (Figure 1), and the sample gas typically follows a more tortuous path through the liner prior to passing out of the split line. This being said, it is perfectly possible for less volatile sample components to condense within the split line and the charcoal trap, which is also included in the split line on most instrument designs. If the concentration of this contamination is high or builds up over a period of time, it is possible for carryover to occur in a very similar fashion to the backflash injection. This can be confirmed, and indeed mitigated, by “steam cleaning the split line” with several large volume injections (typically 5 mL) of water at very high split flows. If the contamination is nonpolar, then ethyl acetate can also be injected in a similar fashion until the carryover is eliminated.

Contamination of Inlet Components

Inlet components such as the liner may become “active” over time, as a result of exposure of silanol groups on the quartz glass from which the liner is made or from any quartz wool packing within the liner or from active metal sites on the inner metal surfaces of the inlet body. This is typically associated with peak tailing phenomena for polar analytes because of unwanted secondary interactions between the analyte and the active inlet site. However, if this interaction is strong, sample components may be irreversibly adsorbed until the following injection. However, again, if the solvent used for the next injection does not readily dissolve the contaminant, the carryover may not occur until an injection of a solvent of the same polarity is made.

To avoid these issues, ensure that deactivated liners are used, avoid the use of glass wool and packing materials within the liner if possible (check the impact on analytical sensitivity and reproducibility and discrimination effects before moving to a liner with no packing), and ensure that the inlet body is regularly cleaned. Liners should be regularly replaced and should be changed as a matter of priority when carryover problems are being investigated.

Carryover from the underside of the septum can also occur if the septum purge flow is not sufficient. This gas flow is designed to flush away septum outgassing products and to avoid sample deposition on the underside of the septum. Many instrument designs have automated control of septum purge flow and so this variable is rarely considered or the flow manually measured. Septum purge flow should be manually measured as part of preventative maintenance routines.

Contamination of Autosampler Components

Finally, the syringe and wash solvents should be considered in any investigation into carryover. Contamination may be carried on the inside and outside surfaces of the syringe needle and this can be somewhat mitigated by using rapid plunger depression and very short residence times for the syringe needle within the inlet. Most manufacturers ensure that this is built into the autosampler routine, however if your instrument provides the option for “slow” or “fast” injection, be sure to choose the fast injection option, especially with splitless injection.

Further, the syringe wash solvents should be matched to the polarity of the potentially contaminating analytes. While most users match the wash solvent with the sample solvent, one needs to carefully consider the solubility–polarity of the components involved in carryover when selecting the wash solvent. Further ensure that waste solvent bottles and the bottle tops are kept clean and regularly emptied. When the autosampler offers more than one wash solvent, one should experiment with the wash solvent routine to minimize carryover—use of one solvent post injection and one solvent pre injection, or the use of both solvents in turn both before and after injection, and so on.

The number of sample washes and syringe primes prior to injection can also be optimized to reduce carryover to the minimum levels. I have known methods that will be carryover free only after five sample washes and five sample primes prior to injection.

Hopefully you will now have a more thorough understanding of the potential sources for carryover that are instrument related and that some or all of this advice will help you to overcome issues with quantitative reproducibility or contaminants in qualitative analysis.

References

1. https://www.chromacademy.com/GC-Sample-Introduction-Best-Practice.html
2. https://www.agilent.com/en/support/gas-chromatography/gccalculators
3. http://m.restek.com/images/calcs/calc_backflash.htm

Akinbuli Opeyemi

www.aasnig.com, opeyemi@aasnig.com

08068129603.

Remove blockages to ICP-OES productivity

Deposition of the sample matrix, salts or even carbon build-up can lead to injector blockage in the torch. How quickly blockages occur varies, depending on sample type, sample workload, torch type, and even the method parameters. A blocked injector can restrict the flow of sample aerosol into the plasma, decreasing sensitivity and
degrading accuracy and precision.
Prevention is the best cure to reduce injector blockage and extend the operating time. Make sure that you are using the recommended torch type and check that you have the recommended instrument parameters for your application. Filter all samples to ensure you remove large particulates. Regular rinsing between samples and at the end of the run can also help to keep the injector clear. However, improper cleaning techniques can permanently damage the
torch. Follow the steps outlined in this technical overview to safely clean your torch, and to remove blockages if or when they occur.

Simple Steps for Clearing a Blocked Injector in Your ICP-OES Torch

Routine cleaning

5100/5110 ICP-OES
– Prepare a 50% aqua regia solution (1 part deionized water to 1 part aqua regia [three parts hydrochloric acid and one part nitric acid]) in a wide diameter tall form beaker.
– Place the beaker under the torch cleaning stand (P/N G8010-68021). This suspends the torch (or injector/base assembly) in the cleaning solution, reducing the risk of spills and damage to the quartz outer tube.
– Invert the torch and position this on the torch cleaning stand so that the quartz outer tube and injector is immersed in the aqua regia solution.
– Pipette some of the aqua regia through the ball joint of the injector to remove buildup from the lower part of the injector.
– Soak the torch for at least 1 hour.
– If deposits remain, repeat the cleaning process using a higher concentration of aqua regia.
– Thoroughly flush the inside and outside of the torch with deionized water (18 MΩ cm) using a wash bottle. Invert the torch and flush deionized water through the quartz tubes so that the water flows out of the gas entry ports and ball joint connector for at least 30 s.
– Invert the torch and dry by blowing clean compressed air or nitrogen through the gas ports on the base and through the opening of the ball joint to remove moisture.

Caution: Do not place the torch in a drying oven. It is not as effective at removing moisture as using compressed air or nitrogen, and may damage the torch.

One-piece quartz torch for 700, Vista, and Liberty Series ICP-OES

– Soak the torch overnight in concentrated aqua regia (three parts hydrochloric acid and one part nitric acid).
– If necessary, use a pipe cleaner dipped in aqua regia to gently remove persistent deposits from the injector tube.
– Rinse with deionized water and allow to dry.

Removing salt deposits
– Rinse the torch with water.
– Soak overnight in a 25% detergent solution.
– Rinse the torch with deionized water and allow to dry.
Important: The torch must be completely dry before re-installing. Replace the torch if chipped, cracked,
or distorted.

Re-installing the torch for 700, Vista, and Liberty Series ICP-OES

– Position the torch in the center of the RF coil, resting on the torch stand.
– Close the torch clamp and turn the locking knob.
– Gently attach the transfer tube to the base of the torch.
– Align the torch so the intermediate tube is about 2 to 3 mm away from the RF induction coil.
– Connect the auxiliary and plasma gas hoses to the appropriate inlets on the torch.
– Complete the torch alignment procedure to ensure the optics are viewing the highest emission signal from the plasma.

Caution:
– Never place a torch in an ultrasonic bath, or use a wire to clean the injector.
– Do not use hydrofluoric acid with glass or quartz sample introduction components.
– Always use care when handling or installing a torch. Excessive force can break the torch.
– Do not touch quartz torches with bare hands. This can
reduce torch life.

– A one-piece quartz torch is simple to install and use and delivers great performance for most applications.
– For organic solvents, use a torch with a smaller ID injector. For volatile organic solvents, use a torch with a narrow-bore (0.8 mm ID) injector.
– For greater flexibility and reduced running costs, choose a semi-demountable torch. The injector and/or outer tube
is removable and replaceable separately.
– For fusions and HF digests, use a torch with an alumina injector.
– A fully demountable torch allows you to replace components individually, which can help lower your operating costs.

Learn how to achieve better sensitivity and precision, and improve tolerance to samples with high levels of total dissolved solids (TDS) by switching to the Agilent OneNeb Series 2
nebulizer.

written by Ayodeji Ogunlowo

ayodeji@aasnig.com

Leak symptoms

GC gas leaks fall into two distinct categories: large leaks that prevent the instrument from functioning and smaller leaks that allow the system to operate, but negatively impact chromatography. Large leaks typically prevent a system from reaching a ready state, leading to an electronic pressure control (EPC) safety shutdown. These types of leaks can result from a column not being installed in the expected inlet, a column not being

connected to the expected detector, a broken column, broken or loose fittings, broken ferrules, cored septa, or tubing blockage, to call out a few possibilities. The cause of these symptoms typically can be rooted out quickly by visual inspection or review of the method settings.

Identifying smaller leaks that allow the system to continue to operate can be more involved. Symptoms of smaller leaks can include constant cycling of actual pressure readings (oscillations greater than 0.02 psi), poor retention time reproducibility, higher than typical background, higher than typical bleed (particularly at temperatures greater than 230 °C), baseline drift, higher than usual inlet activity, tailing peaks, the need for more frequent inlet maintenance, and poor area reproducibility.

Figure 1 shows the elution of US-EPA 8081 pesticides on an Agilent J&W DB-1701 phase before and after exposure to 1,000 μL/L oxygen in helium carrier gas. After just 10 injections, column bleed increased significantly and a shift to shorter peak retention times was apparent

1. No O2 exposure

2. Increased bleed shift to shorter retention after O2 exposure

Figure 1. US-EPA 8081 pesticides before and after exposure to 1,000 μL/L oxygen in helium

Carrier Gas Considerations

High quality carrier and detector gases of known purity are essential for obtaining optimal results in gas-phase analysis. Agilent specifies carrier and detector gas purity of at least 99.9995% (5.5 nines). Zero-grade air is recommended for flame detectors . Inline indicating gas traps are highly recommended to remove hydrocarbon, moisture, and oxygen. Gas certification testing and product descriptions vary by supplier and so obtaining a certificate of analysis (COA) for the gases in use is essential to understand gas quality. On the COA, key items to look for include tests conducted, specification for contaminants, and indications of whether testing was done on individual (preferred) or representative cylinders from a batch

Ferrule Selection

Selecting an appropriate ferrule for the column tubing size and particular fitting being used are critical for minimizing potential leaks and keeping the flow path free of contamination. Agilent J&W columns require one size ferrule for 0.1 to 0.25 mm id columns, while 0.32 mm and 0.53 mm id columns each require ferrules with larger diameter holes to accommodate the wider outside diameter of these columns. Ferrule material choice is also important for achieving the desired results for specific applications. Graphite ferrules are a popular choice for general-purpose and high-temperature applications (above 350 °C) but, typically, are not as contaminant-free as polyimide/graphite or metal ferrules. Further, graphite is a porous material and slightly permeable to gases, creating a very small continuous leak. Graphite also has a tendency to flake off, becoming a source of contamination. Pure polyimide ferrules are recommended for use outside of heated temperature zones only as they shrink dramatically with exposure to heat cycling.

Polyimide/graphite ferrules are a good choice for GC/MS and trace-level analysis, but they also have a tendency to shrink with repeated heat cycles, forcing the operator to snug the fitting repeatedly to avoid leaks. Ferrule shrinkage results in a tendency for analysts to over tighten fittings using polyimide/graphite ferrules.

Flexible metal ferrules are recommended for use with Capillary Flow Technology (CFT) devices as they are specifically designed for the fittings in these devices . Analysts are finding flexible metal ferrules an attractive alternative to other ferrules for standard column connection, such as the split/splitless inlet.

Table 1 identifies some common benefits offered by various capillary column ferrules

Table 1. Ferrule material selection attributes

Avoid Over Tightening

Be aware that over tightening can break the column or permanently damage fittings and actually produce leaks. The Agilent UltiMetal Plus Flexible Metal ferrule was designed to reduce column breakage by ompressing around the column. With a deactivated surface, these stainless-steel ferrules provide a robust and inert leak-free connection. Over tightening of Swagelok, SilTite or UltiMetal Plus Flexible Metal ferrules can damage fitting threads, making it impossible to obtain a seal, and resulting in costly instrument repairs. Carefully read and follow manufacturer’s instructions on fitting installation and use to avoid chronic leaks from

damaged fittings. Proper installation of graphite, polyimide/graphite, inlet seals, O-rings, and septa is also critical to maintaining leak free connections. Just tight enough (JTE) is the goal for proper installation of these somewhat pliable components. If tight is good, tighter is not better (TNB), as these pliable materials and can easily be crushed beyond their design specifications, causing them to leak sooner and more often. In extreme cases with repeated over tightening of brass mass spec transfer-line nuts, the nuts themselves can crack and potentially cause permanent damage to the mass transfer line. The Agilent septum nut has a C-shaped clip at the top that should not be turned more than 3/4 of a turn past where it begins turning with the nut assembly when a septum is being installed. Over tightening of the septum nut will cause premature septum coring with repeated injections, which in turn causes the septum to leak during a run. The septum nut is another fitting that needs to be JTE.

TO BE CONTINUED

 References

Best Practice for Identifying Leaks in GC and GCMS:  Technical Note, Agilent Technologies

 

 

Written by Muyiwa Adebola

muyiwa@aasnig.com, www.aasnig.com

07084594001, 07084594004

By Robert L. Grob, Ph.D., Emeritus Professor of Analytical Chemistry, Villanova University

Most scientists when faced with the analysis of a sample give little or no attention to how the sample was obtained, i.e., the sampling process. This is not the topic of discussion for this editorial. Suffice it to say one should realize that the results of the analysis of a sample can only be as reliable as the sample is representative. One must remember to obtain reliable analytical data three components are always involved:

1) the system (a representative sample), which consists of the analytes of interest and the matrix (the part not requiring analysis but which can interfere with the instrumentation),

2) a measuring instrument, and

3) the analyst or observer (a human being!). Well over 50% of the analysis time is spent on sample preparation and, since you have a human being as part of this system, sample preparation is the most error-prone and labour-intensive task in the analytical laboratory. For this discussion we will assume ALL samples are homogeneous and representative! If the final measurement of analyte concentration is by GC, one should strive to circumvent complete sample matrices; e.g., non-volatile components and interfering analytes.

One criterion for an analyte is that it must have a vapor pressure of 0.1 Torr at operating conditions in gas chromatography (GC). Thus, it must be able to be vaporized in the system inlet. The sample can be a gas, liquid or in some cases a solid (thermally stable or capable of producing a definite pyrolysis pattern). Most sample preparation techniques for GC are based on variations of extraction theory whereby the analytical chemist may change solvent, temperature, pressure, phases or volumes. Thus, an understanding or comprehension of liquid-vapor, liquid-liquid and liquid-solid equilibria are assumed.

IMPORTANT NOTE: Before you attempt the gas chromatographic analysis of an unknown sample obtain as much information about the sample as possible. Randomly injecting an unknown sample into a gas chromatograph does not reveal complete analytical data about the sample!

Having three states of matter (gas, liquid & solid), we have a series of sample preparation techniques available.

Gas-Liquid or Gas-Solid Equilibria

The main sample preparation techniques which can be classified by these equilibria are:

Static headspace technique: analytes of interest (volatiles) are equilibrated in a closed vial at a specified temperature & pressure. A gas-tight syringe is used to transfer the headspace sample into the gas chromatographic injection port.

Dynamic headspace technique: analytes of interest are swept or purged onto an adsorbent and then thermally desorbed into the gas chromatograph.

Solid-phase extraction (SPE): may be used to concentrate analytes from gaseous or liquid samples and often is used to clean up and concentrate liquid extracts. The adsorbed analytes can be eluted with a solvent or thermally desorbed.

Solid-phase microextraction (SPME): may be used for both gaseous and liquid samples. A fused-silica polymer coated fiber (e.g., with polydimethylsiloxane) is exposed to the stirred sample. The shielded-fiber is then inserted into the injection port of the gas chromatograph.

Distillations: these are predominately macro scale techniques and are rarely employed as sample preparation techniques for GC.

Liquid-Liquid or Liquid-Solid Equilibria

The technique of liquid-liquid extraction has lost appeal to the analytical chemist because of

(1) the time needed to reach equilibrium, and

(2) the volume of solvent needed for quantitative recovery of analytes (the environmental restrictions on waste disposal of used solvents).

Quantitative extraction of organic species from aqueous systems requires that the organic moiety

(1) is non-polar,

(2) does not dissociate in the aqueous phase, and

(3) does not dimerize or polymerize in the organic phase.

Thus, liquid-liquid extractions have limitations as sample preparation techniques for GC UNLESS the equilibrium between the two phases exhibits a large numerical partition coefficient. If this is the case, one may resort to micro liquid-liquid extractions, where the concentration factor is >1200 times that for the macro-technique [J. Chromatogr. 106,299 (1975) and J. Chromatogr. 177,135 (1979)]. Thus, classical liquid-liquid extractions have been replaced by modern & efficient techniques and are more prevalent in organic synthesis laboratories or for the separations of metal complexes, metal chelates, and/or ion-pairing reagents.

A number of classical liquid-solid equilibria techniques are available (e.g., ion exchange or Soxhlet extraction) but only Soxhlet extractions have application in sample preparation prior to GC. This technique is not commonly used because:

(a) a large volume of solvent is needed for the sample extraction,

(b) an evaporation step is required to concentrate the sample,

(c) lack of thermal stability and volatility of some sample analytes, and

(d) interference from contaminants in the extraction thimbles (requires a blank extraction prior to sample extraction).

In the past several years, newer techniques have become available. Accelerated solvent extraction (ASE), sometimes referred to as pressurized liquid extraction (PLE) or pressurized fluid extraction (PFE), may be used for solid and semi-solid samples. Elevated temperatures and pressures used in these techniques cause hydrogen bonds and dipole interactions to be reduced, and surface wetting is increased. Water may be used as the solvent if it is below its critical point. Then, it is known as subcritical water extraction (SWE); which makes it similar to SFE.

A similar sample preparation technique is microwave-assisted extraction (MAE); sometimes referred to as microwave-assisted solvent extraction (MWE). The pressure generated is ca. a few hundred psi; however, the extraction container must be microwave transparent (e.g., PTFE or quartz). The solvent used may be microwave absorbing or non-microwave absorbing. In place of microwaves, ultrasonic vibrations may be used to assure good contact between sample and solvent. This is a fast technique but efficiency is not as high as with other techniques. Low concentrations of analytes in samples require multiple extractions. This sample preparation technique is referred to as ultrasonic extraction (USE). A technique which became very popular during the 1980s is supercritical fluid extraction (SFE). Supercritical fluids (SFs) are dense gases above their critical temperature & pressure. Thus, SFs possess properties which resemble both liquids and gases. Analytes are more soluble in SFs when they are in their liquid state; thus, analyte melting points and solubility in the SF are important properties to consider. SFEs are fast and very efficient.

Another group of sample preparation techniques are solid-phase extraction (SPE), solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). SPE is a technique (invented in the late 1970s) referring to a non-equilibrium exhaustive removal of analytes (semi-volatiles and non-volatiles) from a liquid sample by retention on a solid phase (sorbent) and then subsequent removal of selected analytes by solvent elution. Particulate matter in the sample can interfere with the analysis. Thus, particulate matter may sorb some analytes of interest and cause low analytical recoveries.

NOTE: Remove particulates, by filtration, prior to SPE analysis! The efficient use of this technique requires optimization of the sorption and desorption processes.

An extension of SPE, known as solid-phase microextraction (SPME), came about in 1989; the technique utilizes a liquid or solid stationary phase on a fiber, tube, vessel walls, suspended solids, stirrer, or disk/membrane. The technique may be applied to volatiles, semi-volatiles, and non-volatiles and is an equilibrium technique.

An excellent treatment of sample preparation techniques may be found in Chapters 11 and 15 of Modern Practice of Gas Chromatography, R.L. Grob and E.F. Barry (Eds.), John Wiley & Sons, Hoboken, NJ, 4th ed., 2004.

Akinbuli Opeyemi

www.aasnig.com, opeyemi@aasnig.com

08068129603.

 

With recent increases in helium pricing and an increasing number of regulated methods allowing the use of hydrogen as a carrier gas for GC, more labs are looking to switch to alternative carrier gases. This step by step guide will provide you with the necessary information to convert your GC’s carrier gas supply from helium to hydrogen. Hydrogen produced by a gas generator offers a safe, consistent and reliable source of gas as well as being a more convenient and greener source of hydrogen than cylinders.

Once you are satisfied that your method allows for conversion from helium to an alternative carrier gas, follow the steps in this guide to quickly get up and running with an alternative carrier gas while avoiding some of the common pitfalls of switching carrier gas.

Step1. Review all current method information and instrument conditions

1. Review all methods that are run on the GC in the software and make hard copies.
2. Leak-check the GC to ensure that the flow rates in the method will be achieved when running your analysis.
3. Measure all flow rates indicated in your method (septum purge flow, split flow, carrier gas, and detector gases (if applicable), to ensure that the GC is meeting all set points correctly.
4. Keep a note of the linear velocity of your carrier gas.
5. Run a sample and monitor the system to ensure that flows are stable. If any flows change, make a note of these.
6. Keep a record of a good chromatogram to compare with results after changing carrier gas.

Example:

Reference Chromatogram

Step 2. Perform routine GC maintenance before switching carrier gas

1. Change the inlet septum. Use a low bleed septum that is recommended for your GC system.
2. Change the liner. A tapered liner can improve results with hydrogen carrier gas for GC analysis. If you are not using a tapered liner, it may be advisable to purchase some tapered liners before setting up the system.
3. If you are using gas purifiers, it may be advisable to switch these for new ones, depending on how old they are.
4. If you are using a GC-MS and the ion source requires cleaning, this would be a good time to carry this out. Hydrogen carrier gas should maintain the condition of the ion source for longer than helium, so once you have switched carrier gas, you should find that ion source cleaning is required less regularly than before.
5. It is possible to use the same column, provided it is still in good condition. Details are given below regarding conditioning a new column with hydrogen carrier gas.

Step 3. Install new tubing

1. Tubing that was used to supply helium should be discarded. If you use the same tubing to supply hydrogen, you will see high background and it will take longer to optimize your analysis. If you are switching to nitrogen in place of helium for make-up gas, it is also advisable to change this tubing.
2. Within 3m (10 feet) of the application, 1/8” laboratory grade copper or stainless steel tubing should be used. If you are piping gas from a distance greater than 3m, it may be necessary to use ¼” tubing and reduce to 1/8” at each GC. If you are unsure, Peak Scientific can assist you regarding your setup requirements.
3. If you are supplying a GC-MS, you will need to connect just 1 line between the Hydrogen generator and the GC.
4. All fittings should be compression fittings. DO NOT USE SEALING AGENTS or WELD CONNECTIONS. These can introduce volatile organic compounds (VOCs) into the gas stream and contaminate your system.

If you are connecting a GC-FID, you can supply both the carrier gas and fuel gas supply from a single generator. To connect to both gas inlets, prepare a T connection between the carrier and fuel inlets with a single supply line running from the generator. If you are unsure, please contact Peak Scientific for advice on how to connect the generator to your application.

Step 4. Gas supply to GC

The gas generators being used to supply your GC should be installed according to site preparation advice from the manufacturer.

Ensure that the connections into the GC are leak-free using an electronic leak detector – DO NOT USE LIQUID LEAK DETECTORS since these can cause contamination of your gas lines.

Detector gas supply:

1. If your detector requires hydrogen, start the generator and ensure that all connections between the generator and GC are leak-free.
2. If your detector requires nitrogen make-up gas, check that this line is also leak-free by checking before switching on the GC.
3. If your detector requires an air supply, check that this line is also leak-free by checking before switching on the GC.
4. Switch on the GC, making sure that the inlet gas flows are off and check that the detector signal stabilizes.

Carrier gas supply

1. If you are using the column that was already installed, switch on the inlet pressure to allow carrier gas to flow through the column.
2. If you are installing a new column, ensure that the column is correctly installed into the GC inlet. If the column requires conditioning, DO NOT CONNECT IT to the detector. Install the column into the inlet, following the guidelines from your GC manufacturer, ensuring that the connection is leak-tight.
3. To condition the column using hydrogen carrier gas for GC-MS, carefully position the detector end of the column outside the GC oven and very carefully close the oven door, taking care not to break the column. You can see an example of this below:
4. Start the hydrogen flow through the capillary column to purge oxygen and other impurities from the column.
5. Check recommended heating programs and temperatures for the column which you have installed.
6. Once the column is conditioned, switch on the detector, connect the column, and allow at least 1hr stabilization time.

System checkout

1. Once the column is conditioned, connect to the detector and allow at least 1h stabilization time.
2. Check that all method set points are met by the system and are stable.
3. Run a blank sample to make sure that the detector baseline is stable.
4. Adjust the linear velocity of the carrier gas to match the value when using helium carrier gas. Running hydrogen at the same linear velocity as helium, with the same oven temperature program should give you almost identical results. Compare the last chromatogram using helium with the results with hydrogen. The peaks should elute at the same time, but may have a slightly different shape.
5. Compare the reference chromatogram obtained using helium carrier gas with the new chromatogram to ensure that all peaks have eluted and that their retention times are consistent. If there is plenty of peak separation, you can carry out optimization of the method to increase the linear velocity of the carrier gas and shorten run times. You may be able to halve the analysis time in some methods.
6. Ensure that you can identify all peaks in your mixture. Run calibration standards to revalidate the method.

New Chromatogram

 

For enquiry and further information on this product, kindly contact us at Applied Analytical systems Ltd.

Reference:

https://www.peakscientific.com/articles/converting-your-gc-carrier-gas-from-helium-to-hydrogen-:-a-step-by-step-guide/

written by Ayodeji Ogunlowo

ayodeji@aasnig.com

WHAT TO DO IF A MERCURY THERMOMETER BREAKS IN THE LABORATORY

Determining Whether Your Non-Digital Fever Thermometer has Mercury in it : Newer non-digital fever thermometers often use:

• alcohol, or
• A non-toxic compound that looks similar to mercury.

To know if you Thermometer has Mercury

Ask:

• Is the liquid in the thermometer any color other than silver? Then it is most likely alcohol.
• Is it silver? Then it may be mercury or possibly a non-mercury substance.  NOTE: Mercury is a liquid metal with properties different from most substances.  Small droplets will combine into a larger sphere shape, which will roll on a flat surface and break back into smaller droplets if dropped or if pressure is applied. Care must be taken to avoid scattering the mercury or allowing it to roll to a hard-to-reach location.  A standard oral/rectal/baby mercury thermometer contains about 0.61 grams of mercury.

NOTE ABOUT THERMOMETERS WITH SILVER LIQUID: If there is a paper calibration strip inside of the thermometer that includes the words “mercury free”, then the liquid in the thermometer is not mercury. If you do NOT see the words “mercury free”, assume that the liquid is mercury.

 CLEANING UP MERCURY SPILLS

 What NEVER to Do After a Mercury Spill

1. Never use a vacuum cleaner to clean up mercury. The vacuum will put mercury into the air and increase exposure.
2. Never use a broom to clean up mercury. It will break the mercury into smaller droplets and spread them.
3. Never pour mercury down a drain. It may lodge in the plumbing and cause future problems during plumbing repairs. If discharged, it can cause pollution of the septic tank or sewage treatment plant.
4. Never walk around if your shoes might be contaminated with mercury. Contaminated clothing can also spread mercury around.

Prepping for Cleanup of a Broken Mercury Thermometer

• Have everyone else leave the area; don’t let anyone walk through the mercury on their way out. Make sure all pets are removed from the area. Open all windows and doors to the outside; shut all doors to other parts of the house.
• Mercury can be cleaned up easily from the following surfaces: wood, linoleum, tile and any similarly smooth surfaces.
• If a spill occurs on carpet, curtains, upholstery or other absorbent surfaces, these contaminated items should be thrown away in accordance with the disposal means outlined below. Only cut and remove the affected portion of the contaminated carpet for disposal.Items Needed to Clean Up a Small Mercury Spill:

1. 4-5 zip locking plastic bags
2. trash bags (2 to 6 mils thick)
3. rubber, nitrile or latex gloves
4. paper towels
5. cardboard or squeegee
6. eyedropper
7. duct tape, or shaving cream and small paint brush
8. flashlight or small task light
9. optional: powdered sulfur
   • Do not worry if you don’t have this available.
   • The sulfur binds to the mercury and makes clean-up easier. It is sometimes found in the gardening departments at hardware stores, near the fertilizer, or with garden pesticides and fungicides.  Pharmacists may also have it.

Mercury Spill Cleanup Instructions

1. Put on rubber, nitrile or latex gloves.
2. If there are any broken pieces of glass or sharp objects, pick them up with care. Place all broken objects on a paper towel. Fold the paper towel and place in a zip locking bag. Secure the bag and label it as directed by your local health or fire department.
3. Locate visible mercury beads. Use a squeegee or cardboard to gather mercury beads into small mercury balls. Use slow sweeping motions to keep mercury from becoming uncontrollable. Take a flashlight, hold it at a low angle close to the floor in a darkened room and look for additional glistening beads of mercury that may be sticking to the surface or in small cracked areas of the surface. Note: Mercury can move surprising distances on hard-flat surfaces, so be sure to inspect the entire room, including any cracks in the floor, when searching.
4. Use the eyedropper to collect or draw up the mercury beads. Slowly and carefully squeeze mercury onto a damp paper towel. Alternatively, use two pieces of cardboard paper to roll the mercury beads onto the paper towel or into the bag. Place the paper towel in a zip locking bag and secure. Make sure to label the bag as directed by your local health or fire department.
5. After you remove larger beads, put shaving cream on top of small paint brush and gently “dot” the affected area to pick up smaller hard-to-see beads. Alternatively, use sticky tape, such as duct tape, to pick up any remaining small glass fragments. (Peel the tape very slowly from the floor to keep the mercury beads stuck to the tape.) Place the paint brush or duct tape in a zip locking bag and secure. Make sure to label the bag as directed by your local health or fire department.
6. OPTIONAL STEP: It is OPTIONAL to use commercially available powdered sulfur to absorb the beads that are too small to see. The sulfur does two things:
   • It makes the mercury easier to see since there may be a color change from yellow to brown, and
   • It binds the mercury so that it can be easily removed and suppresses the vapor of any missing mercury.

Where to get powdered sulfur? It is sometimes found in the gardening departments at hardware stores, near the fertilizer, or with garden pesticides and fungicides.  Pharmacists may also have it.​

Note: Powdered sulfur may stain fabrics a dark color. When using powdered sulfur, do not breathe in the powder as it can be moderately toxic. Additionally, users should read and understand product information before use.

• Remember to keep the area well ventilated to the outside (i.e., windows open and fans in exterior windows running) for at least 24 hours after your successful cleanup. If sickness occurs, seek medical attention immediately.

Reference

https://www.epa.gov/mercury

https://www.epa.gov/environmental-topics/chemicals-and-toxics-topics

https://www.epa.gov/mercury/what-do-if-you-spill-more-mercury-amount-thermometer

Written by Gabriel Oweh

Gabriel@aasnig.com, www.aasnig.com

08035696303

Troubleshooting vs Maintenance

Troubleshooting:

• Logical, systematic search for the source of a problem
• Helps to identify the cause(s) of a problem with a view
• to correcting it
• Works usually by the process of elimination

Maintenance    

• Activities carried out in order to preserve the operational status and life of an asset (equipment)
• Does not necessarily extend the life of an asset; but lack of it can reduce the asset’s life
• Basically two types: Preventive and Corrective Maintenance
• Preventive Maintenance: Activities that help to detect and prevent failures before they occur or before they develop into major defects.
• Corrective Maintenance: carried out to correct a fault so that a failed equipment can be restored to normal operational status

Maintenance Planning

• Starts before instrument purchase
• Critical factor in the choice of instrument model to be purchased, the instrument configuration and the instrument vendor
• Overall goal is ease of maintenance and low cost of
• ownership without compromising the quality of data
• required from the instrument

Maintenance Planning: What to consider Before Instrument Purchase

• Instrument type, model, and configuration
• Stage of instrument model in manufacturer’s support’s life span
• Availability of adequate and responsive local technical support
• Ease of access to critical instrument parts and consumables
• Local availability/ease of access to high quality reagents, gases etc mandatory for instrument’s operation
• User Training : local or overseas
• Environmental Conditions: Power, temperature, humidity, bench availability, location in the lab

Maintenance Planning: During Installation & Commissioning

• Proper instrument installation
• Installation Qualification
• System Suitability Testing
• User’s Familiarization/Training
• Appropriate documentation: Manuals, reports, lists, etc

Maintenance Planning: After Installation

• Develop SOP
• Develop list of critical spares and consumables and stocking programme
• Develop and setup an Instruments Replacement Schedule
• Develop a planned maintenance programme
• Implement, Review, Take remedial actions, Implement.

Planned Maintenance    

• Also called Preventive Maintenance or Scheduled Maintenance
• It is Pre-planned and scheduled
• Involves scheduled service visits by competent service agent, but may also include periodical checks  and care by User
• Can be date-based or hours-based
• Allows for easier planning of maintenance
• Allows for easier ordering and inventory of spares
• Allows for easy budgeting and costs management
• Allows for an essentially trouble-free instrument life

Impact of Environmental Conditions and Other Factors

Environmental Conditions

• Basically temperature, humidity and light
• Comply with Manufacturers recommended environmental conditions
• Temperature affects instrument stability; high temperature may damage some instrument components and PCBs
• High humidity can also damage instrument components and PCBs
• Use of air-conditioners and/or dehumidifiers may be necessary.
• Light may damage optical components in spectrophotometers

Gases

• Instruments work within precise and specified gas pressure ranges
• Use high quality and functional pressure regulators; preferably 2-stage regulators
• High gas pressures can damage components such as valves and electronic flow regulators in instruments
• Instruments also require highly pure gases devoid of moisture, hydrocarbons and other impurities —–VERY IMPORTANT
• Impure gases can damage valves, electronic flow regulators, GC columns and block GC capillary gas lines
• Use high quality gases and gas filters

Power

• Perhaps, the greatest singular cause of equipment malfunction in developing countries where power supply is irregular and inadequate
• Voltage and frequency very important
• Damage to instrument components can occur due to voltage and/or frequency fluctuation and intermittent power supply
• Facility wiring and grounding also very important and critical
• Use of good quality line conditioners, voltage stabilizers and UPS may be necessary

User

• An untrained User is the greatest source of danger to an equipment, as well as to himself and the facility.
• Users must be trained and qualified in the operation and basic user maintenance of an instrument before they begin to use
• A freshly trained User must use an instrument under supervision until he has demonstrated adequate proficiency
• Properly developed SOPs must be in place and must be understood and followed by all Users

Reference

(C) Muyiwa Adebola, 2017.

 

Written by Muyiwa Adebola

muyiwa@aasnig.com, www.aasnig.com

07084594001, 07084594004