Glyphosate and… Cannabis?

By now, you’ve likely heard of Roundup. Roundup is the trade name for the broad spectrum herbicide developed by Monsanto in 1974 and it’s one of the world’s most widely used agricultural weed killers. Roundup and other herbicides like it contain a polar organophosphorus compound called glyphosate. Glyphosate is degraded predominantly by bacteria into aminomethylphosaphonic acid (AMPA). Another broad-spectrum herbicide that is very similar in structure and global use is glufosinate. The consumption of these compounds have been linked to severe health concerns including but not limited to cancer and concerns are being raised about these compounds contaminating crops, water, and other consumables.

       

 

           

 

                                                      Glyphosate                                                                            AMPA                                                                   Glufosinate

 

Due to the polar nature of these compounds, these analytes are not retained by reversed phase chromatography which is typically used for routine pesticide analysis. To make these compounds more amenable to reversed phase chromatography they can be derivatized or an ion-pairing reagent can be used, but both of these methods have their own set of drawbacks. In this case, derivatization can be performed to add hydrophobicity to the compounds to achieve retention for reversed phase chromatography. The drawback of using derivatization is that it is oftentimes not complete and can potentially become quite labor intensive, adding cumbersome steps and overall time to sample preparation. Ion-pairing reagents are typically used when the compound is too polar to be retained by reversed phase chromatography. The ion-pair reagent contains an ionic head and non-polar tail, kind of like a soap. When added to the mobile phase the hydrophobic tail will interact with the hydrophobic stationary phase and the ionic head of the reagent can retain the polar analyte. Using an ion-pair reagent often results in the need to equilibrate for longer and the reagents are never fully washed from the column.

Recent trends in personal care product and food testing has shown the need to test for glyphosate, AMPA, and glufosinate to determine the potential risk for exposure. The Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) has set a recommended acceptable daily intake of glufosinate at 0.01 mg/kg per day and the sum of glyphosate and AMPA at 0-1 mg per kilogram of body weight per day. (1)

But what does all of this have to do with cannabis? Glyphosate and glufosinate herbicides are currently not approved for use on cannabis crops. Though the use of these herbicides on cannabis crop may be unlikely, there could be potential soil contamination from other sources such as nearby farms contaminating the soil through run off. There could also be cases where contaminated ingredients are used to make cannabis infused products.

As mentioned previously, these polar compounds can’t be monitored by the same reversed phase chromatography that is used for pesticides currently. The Restek catalog of LC columns now offers Raptor Polar X as a solution to the direct analysis of polar pesticides. This column has shown its capabilities to retain glyphosate, glufosinate, and AMPA and has been tested in a variety of different matrices without needing to derivatize or use ion-pairing reagents. An example application can be seen here for spinach.

The question remains, could this the next big thing for cannabis testing labs? Some third party labs have already started this type of testing for personal care products in order to label the products “glyphosate free.” Could “glyphosate free” be the next big selling point for cannabis products? I’d like to open up the comment section to hear your thoughts.

Interested in a certain topic and want it covered in the next blog? Send us an email with your cannabis laboratory/workflow questions and topics and it could be our next blog post!

References: 
1.http://www.fao.org/fileadmin/templates/agphome/documents/Pests_Pesticides/JMPR/2013_JMPR_Summary_Report_Oct_2.pdf

Cannabis Potency Testing & Calibration Curves

Calibration curves are an essential part to potency testing. A question often brought up by customers is “how many calibration points are needed for a calibration curve?” The answer to this question isn’t the same for everyone, as it depends on your laboratory’s objectives and accreditation body guidelines. Since the answer could potentially be different between labs, let’s do some statistics with different numbers of calibration points to gain insight on the effects of choosing more or less points.

Confidence intervals can be calculated for calibration curves and can give us an indication of how close to the “true value” we are when we quantitate samples. This is different from standard deviation, which provides an indication of the precision of a sample. Using statistics we can calculate a range within which the “true value” of a sample will lie by determining the upper and lower confidence limit. This can be performed in excel by using the “regression” function in Data Analysis. Below I have calculated confidence intervals for a hypothetical calibration curve containing either 3, 5, or 7 points using N-1 degrees of freedom and 95% confidence.

Figure 1. Upper and lower confidence intervals calculated for calibration curves containing 3, 5, and 7 points.

The confidence limits were calculated using the same data, just using either 3, 5, or 7 points. If we zoom in on the calibration curve we can start to see the significance the number of calibration points has on the upper and lower confidence intervals.

Figure 2. Zoomed in portion of Figure 1.

When we look at Figure 2 we can see that for more points on a calibration curve the narrower the band is for upper and lower confidence intervals. We can say with 95% confidence that the true value lies within this region. The more points that you have in a calibration curve, the narrower the range that your “true value” will likely occur, so you’re getting a more accurate quantitation for your unknown. As less points are used in the calibration curve the larger the range in which the “true value” could lie and the greater error you can expect when calculating concentration of an unknown.

Now that we understand the effect the number of points has on quantitation, the question next comes up, “how often do I need to run a calibration curve?” The best place to look to answer this question is to your laboratory’s guidelines or SOPs. If your guidelines do not require daily runs of calibrations you can ensure that the instrument is working properly by running daily quality control (QC) points to verify that calibration is still valid. When performing this test, the QC accuracy values should fall between 95-105% to be considered acceptable.

Plotting the points on a calibration curve should result in a linear response. A trend line can be fit to the data to give an equation of the line and R2 value. R2 shows the proportionality of instrument response to quantity being analyzed. In most cases the closer to 1 the R2 value the more linear the line is. There can be instances where you have a value of 0.99 and not have a linear relationship. In these cases lack-of-fit can be more reliable to confirm linear relationship between concentration and instrument response.

The way calibration standards are made can affect linearity. Each standard should be made individually from a concentrated stock solution and not by serial dilution. Serial dilution is when the most concentrated standard is made, and then used to make the next concentration of standard and so on. Serial dilution of standards introduces propagation of error and can adversely affect the linearity of the calibration curve. The concentration of standards should ideally range over 3 orders of magnitude, be within the concentration range of the samples being quantitated, and should fall within the linear dynamic range of the instrument. For instance, if your calibration curve is “flattening out” near the high concentration points then you are reaching the upper limit of your detector and are no longer in the ideal linear range.

Interested in a certain topic and want it covered in the next blog? Send us an email with your cannabis laboratory/workflow questions and topics and it could be our next blog post!

Inhalants of Abuse Libraries Added to Pro EZGC on Rtx-BAC1/2 and Rtx-BAC Plus 1/2 Column Sets

Screening for volatile inhalants of abuse, as well as analyzing for blood alcohol content, is commonly performed in forensic toxicology laboratories using headspace gas chromatography with flame ionization detection (HS-GC-FID). Because these analyses are typically performed using FID detection, they generally use a dual column set-up, allowing for the use of a confirmation column with different selectivity than the primary column. Restek offers two unique column sets catered to these analyses: the Rtx-BAC1/Rtx-BAC2 and the Rtx-BAC Plus 1/Rtx-BAC Plus 2.

All four of these columns have been added to Restek’s Pro EZGC Chromatogram Modeler, with libraries of 60+ volatile inhalants of abuse, along with the typical blood alcohol screening compounds. The inhalants of abuse libraries contain common industrial solvents, refrigerants, as well as nitrites (aka “poppers”) and their bodily metabolites. The Pro EZGC chromatogram modeler can be used to optimize a separation method for your compounds of interest or help to potentially identify unknowns. In addition, one can make changes to parameters such as oven ramp rate, flow rate, carrier gas type, column dimensions, etc., and see the effect it would have on the chromatographic separation instantaneously, without even touching your GC.

The Pro EZGC Chromatogram Modeler can be found here: www.restek.com/proezgc. Once you create a free account and sign into the modeler, there are two ways to search: 1) Enter your compounds of interest. 2) Search by a specific phase and select compounds of interest.

When using the Pro EZGC Chromatogram Modeler, you can enter your compounds of interest and search or you can select from a list of compounds that are modeled on a specific stationary phase.

After you enter your compounds of interest, the modeler, by default, will develop a speed optimized separation on the column that you choose. You will be able to look at a model chromatogram and a list of the conditions used to achieve the separation. You can also use the software to manually alter conditions and see the result on the separation.

Below are some examples of models on the Rtx-BAC columns.

Below is a list of all the compounds that have been modeled on these four columns. I’d be happy to hear any suggestions for additional compounds you would like to see on these column sets.

List of inhalants of abuse and standard BAC screening compounds that have been modeled on these column sets.

Ethylene Oxide – Storage and Stability in Air Canisters

In previous blogs (https://blog.restek.com/cyrogenic-cooling-for-air-analysis-interferences-from-n2-co2-and-o2/ and https://blog.restek.com/cyrogenic-cooling-for-air-analysis-part-2-combining-to-15a-and-ethylene-oxide/) I’ve talked about a combined ethylene oxide (EtO) and TO-15A method, focusing mainly on the chromatography and the use of cryogenic cooling to achieve separation of EtO from the several possible critical coelutions. However, it doesn’t matter how good the chromatography is if you can’t get your sample to the instrument, and I’ve been finding that EtO has some surprising complications with canister sampling. The EPA has mentioned this as well, with an update to EtO background sampling stating that “Recently, EPA has been examining whether aspects of the canisters used to collect air samples may cause some results to be biased (https://www.epa.gov/sites/production/files/2020-09/documents/background_eto_monitoring.september_2020.pdf).

So, what exactly does this bias look like? If you were fortunate enough to attend the virtual National Environmental Monitoring Conference (NEMC) in 2020, you may have caught a talk I gave on this exact topic. For those of you who didn’t attend, you can find a copy of the presentation at https://apps.nelac-institute.org/nemc/2020/docs/presentations/pdf/8-4-20-Air%20Methods,%20Monitoring,%20and%20Technology-4.02-Hoisington.pdf. What we’ve found is that a positive bias in EtO seems to be tied to two things – the fill gas (humid air vs. dry air or nitrogen) and canister cleanliness.

Let’s start with the fill gas. We had received customer feedback that some canisters they had in use for EtO were checking out clean in the lab, but giving abnormally high results when used in the field. When we checked out the canisters in question in our lab we found some background EtO present, but only if they were filled with humid air. Dry air or an inert gas such as helium/nitrogen were non-detect for EtO. This matched with the customer experience, as they used nitrogen to clean and fill canisters for blank checks.

 

Table 1: Comparison of EtO blanks using different fill gases. Average of 3 samples.

 

We found that this background EtO contamination was something that occurred regardless of the canister typed used, whether it was a plain electropolished TO-Can or a SilcoCan. Testing 2 competitor canisters equivalent to our SilcoCans also revealed growth of EtO over time when filled with 50% RH air.

Figure 1: Graph of EtO growth for various canister types in 50% RH air. Average of 3 samples each, error bars are 1 standard deviation.

In case we haven’t made the point enough in our TO-15A blog (https://blog.restek.com/the-new-u-s-epa-method-to-15a-blog-series-part-5-humidification/), this really underscores the need to use humid air when qualifying canisters. The use of dry air or inert gas can mask possible issues with your canisters for EtO and other compounds, including some volatile sulfur compounds (https://www.restek.com/Technical-Resources/Technical-Library/Air-Sampling/env_EVAR3325-UNV).

You’ll note that one of the competitors was significantly higher than every other canister tested, which brings us to the second point – canister cleanliness. When we look at the chromatograms of these canisters, as well as some customer canisters that we were told had issues with EtO bias we see that they have a significant amount of unknown contamination at the end of the chromatogram, much higher than the internal standards.

 

Figure 2: Comparison of canister cleanliness. Black – customer canister. Blue – Competitor canister. Red – Restek TO canister.

 

In addition, we had some customer canisters that had seen heavy use in the field and were now having cleanliness issues unrelated to EtO. When we tested those cans not only did they show a very high amount of contamination in the semivolatile range, they also had a high level of EtO, with blanks at 5.9 ppbv. After thoroughly cleaning the canister using a proprietary cleaning process, the semivolatile contamination was gone and the background EtO became ND.

Fig. 3 – Customer canister with heavy field contamination and 5.9 ppbv background EtO (top). Customer canister after cleaning, ND for EtO. Filled with 50% RH air, analyzed 7 days after filling.

This seems to indicate that EtO can be produced by oxidation of larger contaminants built-up in canisters, possibly catalyzed by the presence of water and the metal surface. Even canisters that have not seen field use, such as the ones used to generate the data in figure 1, show measurable EtO growth over time. If you are using selective ion monitoring (SIM) to improve your EtO detection limits and check your cleaned cans using only the SIM method you’ll likely miss the semivolatile contamination that seems to be correlated with high EtO growth, so the use of full scan MS is highly recommended when testing for canister cleanliness. If you are currently performing EtO analysis, or planning to do so in the future, then the use of humid air and full scan analysis will help you determine if you canisters are suitable for EtO.

Analyzing THC Concentrates? Look for Isomers!

As we learn more about the chemical constituents of cannabis, more cannabinoids are being discovered and with it more THC isomers. You are probably very familiar with the two most commonly tested: Delta-9-THC and Delta-8-THC https://www.restek.com/Technical-Resources/Technical-Library/Video-Library/Did-You-Know-THC-Has-Isomers. There have been a total of 30 different isomeric forms of THC discovered thus far including different conformations. These isomers all share the molecular formula C21H30O2. In this blog, we will be focusing on isomers of THC that vary by the location of the double bond located on the methylcyclohexene ring.

Delta-9-Tetrahydrocannabinol

Also known as: THC, dronabinol

Delta-9-THC is the main psychoactive component found in cannabis. This compound has a double bond on carbons number 9 and 10 and was listed as a Schedule I drug by the UN Convention of Psychotropic Substances in 1971 and remains federally listed in the US as Schedule I substance today. In the United States, when the 2018 Federal Farm Bill was passed, hemp products were allowed to be sold as long as they do not contain more than 0.3% of delta-9-THC. In the body, two metabolites are formed from delta-9-THC; 11-hydroxy-THC and THC-COOH.

Delta-8-Tetrahydrocannabinol

Delta-8-THC is an analogue of Delta-9-THC and only differs by the placement of the double bond on carbons number 8 and 9. It is also psychoactive but is potentially less potent. The passing of the 2018 Farm Bill in the United States initially did not include language for delta-8-THC, allowing this compound to fly under the radar, but has since become illegal to convert CBD into delta-8-THC in several states. Delta-8-THC produces hydroxylated and carboxylated forms of delta-8-THC in the body, similar to the delta-9-THC metabolites.

Exo-Tetrahydrocannabinol

Also known as: Delta-9,11-THC

Exo-THC differs from the other two isomers by the double bond location on the methyl group located on carbon 9. This compound is not typically found naturally in cannabis and could potentially be an indication of synthetic THC or formed during an extraction/sample preparation procedure.1 Its metabolites are similar to delta-8 and delta-9 forming hydroxylated and carboxylated compounds but with the location on the double bond on the methyl group of carbon 9.

Delta-10-Tetrahydrocannabinol

Delta-10-THC has the location of the double bond between carbons 10 and 10a. It is thought to not have psychoactive effects but testing is somewhat limited and could have diluted psychoactive effects.

As I mentioned before there are many more isomers but for this blog we’re going to stick with these four because of current interest. It’s important to be able to separate these isomers if you need to perform a potency test on concentrates to obtain accurate quantitation for each compound. These THC isomers all have their own benefits and as more are being discovered, there is more interest for potency testing labs to be able to detect them.

Here, a method has been developed to baseline separate four THC isomers, exo-, delta-8-, delta-9-, and delta-10-THC in 4 minutes using an isocratic method. By implementing an isocratic method you can cut down on overall run time by eliminating the equilibration step between runs.

By using this method to look at THC concentrates, your lab can cut back on instrument time due to the rapid analysis and save money by using methanol as opposed to acetonitrile. This method also allows for baseline separation of all four isomers allowing for accurate identification and quantitation.

While we are discussing new cannabinoids of interest, I want to direct your attention to two recently discovered cannabinoids that have recently been added to our cannabinoid assays, tetrahydrocannabiphorol (THCP) and cannabidiphorol (CBDP).2 The traditional analysis for 21 cannabinoids can be found here, the Solvent Saving method for 21 cannabinoids can be found here, and a rapid analysis method can be found here.

Interested in a certain topic and want it covered in the next blog? Send us an email with your cannabis laboratory/workflow questions and topics and it could be our next blog post!

References:

  1. Society of Cannabis Clinicians July 27th, 2020. “What is exo-THC?” https://www.cannabisclinicians.org/2020/07/27/what-is-exo-thc/
  2. Linciano, P., et al. Journal of Natural Products, 2020, 83 (1), 88-98.

 

Is my LC instrument generating high pressure by itself?

We have had several blog posts and articles that discuss high backpressure observed in LC systems. Much of this discussion involves how to determine if the problem is in the column and what to do about it. Here are links to several of these:

The Clog Blog

Building up pressure on HPLC?

Technical Service Red Flags- LC

BUT, wait – what if the problem is not the column? Where is it coming from? Our Technical article here does a great job of discussing all of the possibilities: Diagnosing and Preventing High Back Pressure in LC Systems.

One common source of high backpressure mentioned in the above article is instrument “wear and tear”. Components like pump seals and rotary valves can shed materials, often in the form of what I would call “shavings” that may get into the flow path and become lodged at some point downstream.  A common place for this material to be lodged is on the front of your guard cartridge or (if not using a guard) the inlet of your column. This is one of the reasons it is important to have a preventative maintenance schedule. Something that is also often overlooked is the possibility that this type of particulate may break loose right after a maintenance procedure is performed, such as a seal replacement, valve repair or valve replacement. For that reason, the analyst should completely flush all tubing in the flowpath and check the system pressure before connecting the column. It is also a good idea to inject a series of solvent blanks before connecting the column to ensure everything is working properly.

You might also find the following related resources helpful:

Routine LC Maintenance: Simple Steps to Preventing Unexpected Downtime

Preventing LC Column Clogs (Video)

Do I need an LC Guard Column? (Video)

 

I hope you found this helpful and thank you for reading.

Method translation and PLOT columns – Analysis of gases on Alumina column

One of the tools we can’t live without when modifying/developing a GC method is the EZGC method translator. Changes made to GC method parameters like; inlet/outlet pressure, flow/carrier gas type or even capillary column dimensions will result in different retention times for our analytes and will affect resolution. Method translators calculate new analysis conditions by keeping the analytes’ elution temperatures the same, thus preserving the elution order. Using this tool, the analysis method can be translated to a different column dimension, carrier gas type, linear velocity, for example, with very little time spent on the method development. Method translation works well for the columns with a liquid stationary phase. But how well will it work with PLOT columns?

There are two reasons we thought it would not be accurate for PLOT columns:

  1. Inaccurate flow control due to flow restriction through the column.
    Thick layers of particles are difficult to deposit in an even layer. Uneven coating thickness could affect the column internal diameter/flow (1).
  2. PLOT column chromatography or gas/solid chromatography is based on adsorption/desorption principles – a surface process. Do the same rules work in gas-solid as in gas-liquid chromatography?

To prove the concept, I used an existing method, ASTM D2712 (2), analysis of hydrocarbon impurities in propylene. The method is essential among the propylene producers since propylene is a starting material for many plastics and chemicals. Its purity determines the quality and price. While the analysis is run on a 4-column analyzer, the main analytical column is the Alumina/KCl BOND, and that’s the column I’ll test for this demonstration.
I translated the original method from helium carrier gas to nitrogen and hydrogen using a “Translate” function (Figure 1) – translation to alternative carrier gases. The column length was determined by counting the number of column loops on the cage (3). I was glad the calculated number matched the length of a new column – 50.5m. A faster technique to determine the column length is to measure the column hold-up time (4). However, this approach will not work with Alumina columns because even the lightest analytes, like methane, show some retention. Since I was using FID, there aren’t many other options for unretained compounds.

Figure 1: Translation with the EZGC Method Translator using Alumina/KCl BOND 50m x 0.53mm x 10µm column and helium carrier gas to hydrogen and nitrogen.

Figure 2: Chromatograms using all three carrier gases and translated analysis conditions, respectively.

The obtained chromatograms above (Figure 2) show a similar elution pattern. Additionally, I used the retention times and oven temperature profile to calculate the analytes’ elution temperatures for all three carrier gases. Given that the main principle of the translation is to preserve the elution temperature from one analysis to the other, we should expect minimal deviation between the calculated elution temperatures. (Figure 3, last column). Further, I compared predicted retention times (calculated using speed factor) to the actual retention times (Figure 3). I could not expect better results for both carrier gas and the minor deviations attributed to the estimated column length.

Figure 3: Retention time of the analytes using all three carrier gases, calculated elution temperature, and predicted retention times.

The second parameter investigated was the resolution. Despite the considerable differences between the analytes’ retention times, I noticed little change in the resolution with slightly better numbers when using a nitrogen carrier gas. I plotted the resolution numbers below (Figure 4). Closely eluting compounds, where we strive to maintain resolution, showed a very narrow standard deviation window.

Figure 4: Comparison of resolution numbers obtained using all three carrier gases

 

Alumina columns and hydrogen carrier gas
We confirmed that with minimal method development (just entering the numbers in the method translator), we could translate the analysis method to any alternative carrier gas. However, some customers have reported unusual results when using alumina columns with hydrogen carrier gas. At higher temperatures, alumina columns may become reactive and catalyze cracking/hydrogenation of the unsaturated hydrocarbons. While I didn’t notice any unusual behavior on the KCl column, I suggest that you check column performance during the method validation step.

Literature:

  1. https://www.restek.com/Technical-Resources/Technical-Library/Petroleum-Petrochemical/Restek-s-PLOT-Column-Family-PCSS1163G-UNV
  2. https://www.astm.org/Standards/D2712.htm
  3. https://blog.restek.com/do-you-measure-the-length-of-your-gc-column/
  4. https://blog.restek.com/short-webinar-on-calculating-column-length-using-ezgc-flow-calculator/

Chemical Reference Standards: Don’t Just Snap and Pour (Part 2)

Several years ago, my colleague, Alan Sensue wrote Chemical Reference Standards; don’t just snap and pour. In it, he described a personal experience where he mixed several expensive reference standards together assuming the vials contained exactly 1 mL. It was a mistake he has remembered for some time. Here are a few other examples as to why you don’t want to just snap and pour your reference standards:

Before opening the vial, it is a good practice to examine it and its contents. During shipment, vials can get bounced around on the delivery truck. As a result, a portion of the solvent can adhere in the top half of the vial. By lightly tapping the bottom of the vial on a lab bench, or lightly flicking the top of the vial with a finger, the solvent should flow to the lower portion. The below photo demonstrates what could happen. The standard was easily aliquoted into a secondary container, but appears to have less than 1 mL provided. If you look closely at the snapped off top, half the solution has remained there. Don’t just snap and pour.

Some compounds, such as PAHs, cannabinoids, and PCBs may fall out of solution when stored refrigerated or frozen. For stability purposes this is the recommended storage. Prior to using these solutions in the lab, the vial contents should be examined. If you see something similar to the vial below, sonication and/or heat may be required. Once the standard is at room temperature, place the solution in a sonicator for 10-15 minutes. Additionally, a little heat (around 40°C) can help dissolve these compounds back into solution. By doing so, you will not be “missing” these compounds from your assay. This was mentioned in Handling Your Analytical Reference Standards. Additionally, this post emphasized to follow the instruction on the standard’s Certificate of Analysis (CoA). Don’t just snap and pour.

There are a handful of Restek reference standards that are solids, where the composition is based upon % by weight. In the case of these standards, only 50 to 100 mg of material may be present in the ampule. This small volume will appear as a film or a small pinhead size glob. Like the example below, there’s nothing wrong with those standards. It is only the small volume received. In this case, once snapped, you cannot pour.

In summary……
Pay attention to the information contained on the CoA. Follow the storage conditions. Examine the vial and its contents prior to use. Make sure all components are in solution. Have the solution in the bottom half of the vial to aliquot or transfer. Finally, accurately measure all of your aliquots. Don’t just snap and pour.

Pro EZGC Library Update: Cannabinoid Neutrals!

Every once in a while, I meet a customer who is interested in analyzing cannabinoids by GC. Before Pro EZGC, these requests were difficult since we could only guess on the resolution and conditions.  Through the power of Pro EZGC and some previously published blogs, I was able to come up with a column and conditions. So, without further ado, I would like to welcome the neutral cannabinoids to the family of modeled compounds! Currently, this class of compounds is available on the Rxi-35Sil MS. The list includes:

  1. delta-9-THC
  2. delta-8-THC
  3. CBD
  4. CBC
  5. CBG
  6. CBN
  7. CBL

For those looking to save time in the lab by modeling and gathering run conditions for cannabinoid analysis by GC, click the link to check out Pro EZGC Chromatogram Modeler. Happy modeling!

 

Example chromatogram: cannabinoid neutrals using Pro EZGC.

Troubleshooting GC Column Baseline Issues

Every GC analyst experiences baseline issues at some point in their career, whether the baseline is higher than normal, or it contains additional peaks/spikes, or becomes erratic and drifts up and down.  In order to fix the baseline issues you will need to determine the cause.   I hope that the information contained in this post, and within the links it contains, will help you troubleshoot and remedy your GC baseline issues.

 

High Bleed

Symptoms:

  1. Abnormally elevated baseline compared to previously obtained/expected baseline for the same (or equivalent) GC column for the same instrument and detector.
  2. Baseline keeps rising at high temperatures even when only injecting safe GC solvents like acetone and hexane.
  3. Occurred after injecting one or more samples/standards that exceeded the recommended safe pH range of 5 to 9.
  4. Occurred after injecting derivatized samples/standards, especially if the derivatization reagent was not completely removed prior to injection.
  5. Occurred after overnight conditioning/bake-out.
  6. Are you using a low-bleed column?

 

Solutions:

  1. GC columns are a consumable and do not last forever. Install a different GC column; one you know has low bleed, to confirm the instrument is not the issue.
  2. Leak check using an electronic leak detector. Even the smallest leak can damage a GC column’s liquid stationary phase in minutes at high temperatures.
  3. Never inject strong acids or bases.
  4. Never inject derivatization regents directly into any GC column unless you are certain that damage will not occur.
  5. Only condition a GC column until a stable baseline is achieved. Longer conditioning may reduce column life.  Make sure to use high quality gas/filters for the carrier gas.  Removal of oxygen and moisture is necessary for the longest column life.
  6. Not all GC columns are considered low-bleed. For example, porous polymer PLOT columns have much higher bleed than low-polarity liquid phase columns.  For GC columns which are not considered low-bleed, use them only for the analysis they were designed for and at the lowest GC oven temperatures which your analysis will allow.

 

Additional information:

GC Troubleshooting—High GC Column Bleed

GC Column Conditioning

10 Places to Check for GC Gas Leaks

Why do porous polymer PLOT columns bleed more than Liquid phases?

Not checking for leaks in your GC system has consequences

Exploring the upper temperature limits for a wax GC column

Capillary GC Column Killers – Part 1

Capillary GC Column Killers – Part 2

 

Extra Peaks or Spikes

Symptoms:

  1. There are peaks in the chromatogram that were not previously there, and should not be there.
  2. There are noise spikes in the baseline. Spikes are commonly observed rising from or dipping below the baseline.   They are often too narrow to be a compound peak.

 

Solutions:

  1. The liquid stationary phase in most GC columns do not typically produce distinct peaks. These “ghost” peaks are commonly caused by contamination.  However, the liquid stationary phase may produce jagged peaks (see section below) in certain high-polarity and non-bonded columns.
  2. In many cases, spikes are electronic noise from the detector caused by a poor connection or corrosion of electronically energized parts. Particulate matter passing through the detector may also cause spikes.

 

Additional information:

Trimming a GC Column to Remove Contamination

GC Troubleshooting—Carryover and Ghost Peaks

Poster on sources for “Ghost-Peaks” in Gas Chromatography

Unraveling the Mysteries of Ghost Peaks: It’s Time to Pull the Sheet Off

Are your ghost peaks coming from the GC column, or something else?

Column Bleed & Septa Bleed – Same Old Thing!

 

Wavy/Fluctuating Baseline and Jagged/Noisy Baseline

Symptoms:

  1. Baseline which is not flat or consistent, even at isothermal temperatures.
  2. Baseline which has multiple rises and dips in a short period of time. These changes typically occur faster than baselines which have a wavy or fluctuating baseline.

 

Solutions:

  1. May be caused by poor quality gases, including but not limited to carrier gas, fuel gas and/or make-up gas. Could be caused by temperature fluctuations.   Unstable detector.
  2. A jagged baseline can be caused by ramping a GC oven column too quickly, especially high-polarity and non-bonded columns. Limit both the GC oven column heating and cooling cycles to a maximum of 20°C/min.

 

Additional information:

Did you know you can manage jagged bleed with a controlled cooling program?

GC Troubleshooting Poster

Why does my GC Need Clean Gas?

 

Elevated (High) Baseline

Symptoms:

  1. A rise or fall in the baseline that is not related to an increase or decrease in the GC oven temperature.
  2. Occurs when analyzing “dirty” samples.
  3. Becomes worse when the injection volume is increases.

 

Solutions:

  1. Set the GC oven to an isothermal temperature and without injecting anything, monitor the baseline. If it remains elevated for long periods of time, that is likely the baseline for this column at this point in its life.  Refer to section on High Bleed.
  2. Elevated (high) baseline may be caused by contamination (matrix) and not just the degradation of the liquid stationary phase. Additional sample clean-up may be needed.
  3. Baseline may be caused by injection solvent or other vapors remaining in the injection port. Check for injection port leaks and possible plugging/contamination issues with the split vent line and filter.

 

Additional information:

No Injection Instrument Blanks for GC

Why does my column have high bleed?

Contamination of Injection System Split-Vent-Lines