Trade in Splitless for Split: Faster Speed & More Miles Analyzing 3-MCPD / Glycidyl esters

In my recent work with analysis of 3-MCPD and glycidyl esters, I reviewed the available methods by AOCS and they list splitless or pulsed splitless injection. Splitless injection theoretically transfers all of the sample onto the column, allowing the analyst to achieve trace levels of detection. However, there are limitations. Both splitless hold-time and focusing (or lack thereof) have an effect on peak shape (broadening and tailing) when set incorrectly. Another consideration is the presence of derivatization agents which can damage and decrease column lifetime. The split injection (shoot-and-dilute approach) overcomes these limitations, however, since the majority of the sample is vented there is concern about achieving adequate sensitivity. There is an excellent blog about using this approach for the analysis of used motor oil here! Read the rest of this entry »

SPME Fundamentals: A Look into Incubation and Extraction Temperatures

Being fairly new to anything comes with some good lessons learned. My recent foray into Solid Phase Microextraction (SPME) has been a lot of fun, but I’d be lying if I said it has not been frustrating, complete with some face-palming moments.

 

 

In this series, we are going to take you on a journey, looking at different SPME parameters. Not only do we hope that this series will teach you about the fundamentals of SPME, but also that it can assist you during method development.

To kick off this series, we are going to start with how incubation/extraction temperature affects compound response. This will cover compounds ranging from very volatile to semi volatile compounds. This topic originally came up during some method development for a residual solvents in cannabis products application (check out that series here!) where we wanted to move from a headspace syringe (HS-Syringe) method to a headspace SPME (HS-SPME) method. Not having the most experience with SPME, it was thought that we could just take our HS-Syringe parameters and use them for the HS-SPME method. And as you may have guessed, we were wrong.

To understand what temperature is best for doing HS-SPME (keep in mind that we are using the SPME Arrow for this study), we set up an experiment where we tested incubation/extraction temperatures from 30°C to 80°C and then compared each compound’s averaged area.

 

 

This was also compared to the HS-Syringe, where the incubation temperature was set to 80°C, which is a traditional temperature for this type of analysis.

 

 

 

 

These results are very interesting. Just looking at the HS-SPME results, having an incubation and extraction temperature of 30°C gives the best response for the hydrocarbons, especially for the hydrocarbons that have higher boiling points. The more polar compounds respond a little differently though. For example,the response increases for methanol and ethanol as the incubation and extraction temperature increase. These samples are in water, so it makes sense that these compounds need higher temperatures to partition out of the water and into the headspace. However, for the majority of the compounds (17 out of 22) HS-SPME at 30°C gives better response than at 80°C.

When the HS-Syringe method (80°C, 45 min) is compared to the results for HS-SPME (30°C-80°C, 2 min), the HS-Syringe does give better response for some compounds, but when taking in all of the data, the HS-SPME results are very close and for the majority of the compounds, it gives much better response in a fraction of the time.

So, why does HS-SPME at 30°C give better response than at 80°C for the majority of the compounds? I mean come on, more is always better, right?

Well, as Pawliszyn pointed out in 1995, high temperature can have an adverse affect on the absorption of analytes to the fiber coating. This is due to the decrease of partitioning coefficients, meaning that at higher temperatures, while the analytes will release from the matrix, does not mean that they will absorb to the fiber coating. The analytes are more soluble in the fiber coating at lower temperatures versus higher temperatures and this makes a lot of sense knowing that to desorb the analytes off the fiber and into the gas chromatograph requires the inlet to be at higher temperatures rather than lower.¹

If you have encountered this problem before, when switching from a traditional HS-Syringe method to a HS-SPME method, we know how you feel! Luckily, if you simply adjust your incubation temperature, you should see a nice boost in response for most of your compounds of interest!

It is important to note that the incubation time for all of above results was 120 s and the extraction time was 120 s for the SPME Arrow. Perhaps one could incubate and extract for less time at the higher temperatures. However, clearly higher temperatures were detrimental at the current times. Stay tuned in the future when we look at incubation time.

 

 

References:

  1. Quantitative Extraction Using an Internally Cooled Solid Phase Microextraction Device. Zhouyao. Zhang and Janusz. Pawliszyn Analytical Chemistry 1995 67 (1), 34-43

 

 

 

 

Sorry for the delay. Here is your chromatogram with and without the PFAS Delay Column.

Sometimes I hear this from customers: “I don’t need a delay column. I haven’t had any trouble without it so far.”

It might be true. You may not have any issues without the delay column, especially when your samples are, for example, highly PFAS contaminated soil samples because the interference is too small to affect your end result.

I’ll show you the difference between PFAS analysis with and without the delay column.

Don’t be surprised. The chromatogram on the left is a blank sample injection! As you can see, there are peaks at the retention times you would expect the compounds from your sample to come out. Imagine what can possibly happen if you don’t have the delay column and you inject your sample containing low levels of PFAS.

                    

The chromatogram on the right also shows a blank sample injection, but this time the PFAS delay column was installed. You can see that the sharp peaks disappeared, but where are those delayed ”peaks”?   The elevated signals coming AFTER the expected retention times of the compounds of interest are the system-related PFAS that were held up by the delay column.

Remember the PFAS delay column is installed BEFORE the injector in the LC-MS/MS workflow and system-related interference will enter the delay column in a continuum from the mobile phase bottle and make their way through the analytical column to the detector. Unlike the injections of your sample which focus analytes at the head of the analytical column before the gradient starts, the interferences are continuously fed and they will be retained as they go through the delay column, diluted as they go through the injector, then retained again on analytical column not necessarily being focused much at any stage; hence resulting in broad and elevated signals.

Yes, the delayed interferences are broad because they enter the system continuously, and the signal is only elevated instead of looking like a sharp peak because the interferences exist from the very beginning of your analytical workflow (mobile phase) and are never focused on the analytical column like your sample. The magnitude of the delayed signal elevation depends on how long you equilibrate your LC column (length of column equilibration is related to how much your LC-MS/MS system components leach out the interferences onto the delay column) and what LC-MS/MS system you use (different LC-MS/MS systems may have different levels of system-related interferences depending on the materials used in various component parts).

Another way of minimizing system-related interferences is to replace all plastic parts in the workflow which may have PFAS leachates with PFAS-free parts such as PEEK. Still, the possibility of having background interferences from the workflow is endless since different LC-MS/MS systems may need different parts to be replaced. This approach might be too time-consuming to be practical, and you can still struggle with finding unknown sources of the interferences.

Sometimes you may analyze PFAS samples with high concentration for remediation projects,  e.g. contaminated soil from military bases or fire department practice sites, and sometimes your samples can be drinking water samples, which usually require low level detection (parts per trillion or even below).

Regardless of the LC-MS/MS systems you use for PFAS analysis and the level of concentrations you work on, having the PFAS delay column installed in your workflow BEFORE the injector will make you headache-free in your method development, method validation, and your day-to-day PFAS analysis.

Cannabis Residual Solvent Method Development Made Easy with Free Modeling Software

In a typical cannabis testing laboratory, finding time and resources to improve or develop methods can be scarce.  Even in our own applications group, finding time to “quickly” generate data can be a challenge with multiple projects taking place at the same time.  However, there’s a tool that can help make this process more efficient and alleviate some of the burdens that you might encounter during this process.

Recently, I received an external inquiry regarding our Cannabis Residual Solvent Mix #1 (cat.# 34105).  During the email conversation, I shared a chromatogram and method which Colton developed last year.

After sharing the method, I was asked if we offered a standard for ethylene oxide and had any supporting chromatograms using the same conditions above to show where the compound eluted since our customer wanted to develop a method for California’s residual solvents list.  Unfortunately, we didn’t have this chromatogram.  To make things worse the instrument needed to generate the chromatogram was running samples for another project.  Yet, within minutes of Colton informing me of this news, he generated a model chromatogram containing ethylene oxide using his run conditions.

 

How was this possible?!?!  We have Pro EZGC® Chromatogram Modeler to thank for this!  This free program allows users to spend a little time in the office to save a lot of time in the lab.  To find out more about EZGC, check out Chris English’s post “I Can’t Drive 55” – The Pure Power of EZGC.

https://blog.restek.com/?p=8195

And thanks to Colton’s quick thinking we were able to answer our customer’s questions in less than a day.  So the next time you’re planning to modify a method or develop a new one, use the Restek Pro EZGC® Chromatogram Modeler to help you get started!  https://www.restek.com/proezgc

Does your cannabis lab need a Residual Solvents standard? Look no further, friend!

So, we got the news. Cannabis labs and application chemists are sick and tired of residual solvent standards in DMSO. Instead of continuing to offer you something that can be difficult to work with, we put our heads together at Restek to offer you a new RSA standard in N,N-Dimethylacetamide (DMA)!

Not only is this standard offered in the preferred solvent across the industry, but it also includes 20 of your favorite compounds at 3000 ppm! The Residual Solvents #1 (cat# 34105) CRM pairs very nicely with some Topaz Liners (cat# 23280) and the Rxi-624Sil MS (cat# 13868). Finally, when we combine all three of these products, we are left with the delicious solution shown below.

 

You can also check this out on the web here!

 

So, if you’ve been trying to get your hands on a residual solvent standard, look no further! Restek has you covered!

 

Be on the look out for more Cannabis reference standard solutions. We’ve got some good stuff brewing up!

Photo Credit: DavidCardinez

 

 

An introduction to radiello: a passive, diffusive air sampling badge for VOCs

Today, Restek launched the radiello passive, diffusive air sampling badge for VOCs. Oh… so you do not know what that is. Well then, be sure to check out the following video, which will give you an introduction to radiello:

Stay tuned for future blogs featuring how to properly utilize the radiello.

Totally serious analysis of N2O – capillary column selection

A few years ago, Jaap wrote a blog, “Can I analyze NO, N2O and NO2 via GC?”, which received a vast response. If you are just starting to dive into the analysis of N2O, scroll through the blog comments where you can find many valuable insights from our blog readers. What I would like to show now is the selectivity of capillary columns capable of separating N2O from permanent gases.

While N2O is considered a greenhouse gas, it has a variety of beneficial uses in multiple industries. We all know it as “laughing gas”, thus the analysis is commonly done in medical and forensic labs. N2O is soluble in fat and inhibits bacterial growth, which makes it an ideal propellant in cans of whipped cream. It’s also a powerful oxidizer, yet stable at room temperature, so it powers our rockets into space. Analysis of this light gas is often performed in the ppb concentrations in atmospheric samples. So, all the mentioned characteristics make it an easy gas to analyze using gas chromatography. Separation of N2O from permanent gases at room temperature can be attained using almost any adsorbent column. The large surface area of those materials offers enough retention for the light analytes to separate without using sub-ambient temperatures. Analysis times will be short, and any injection errors (e.g. system dead volume or slow sample transfer on column) will lead to peak broadening, affect resolution between the components, and raised system detection limits.

Rt Q BOND column is often a number one choice for this analysis. CO2 (3) and N2O (4) will be separated at 40°C with enough resolution that even overloading a column (observed as peak tailing) will not interfere with peak integration (blue chromatogram overlay).

Column: Rt-Q-BOND 30m x 0.53mm x 20µm (cat.# 19742); Sample: 0.1-0.5% permanent gas mix with nitrous oxide and C2 hydrocarbons (black overlay); Injection: Inj. Vol.: 200µl, split ratio 10:1; Oven Temp: 40°C Isothermal; Carrier Gas: He, constant flow 5.1 ml/min; Detector: TCD; Notes: Blue chromatogram overlay is 200µl injection of 80 vol% carbon dioxide and 20 vol% nitrous oxide. Overlays are not in the same y scale (blue is compressed).

Although GC-µECD[1] or GC-MS[2] detection are generally preferred over the TCD, TCD is an easy to use universal detector that can be used when N2O concentration is above 50 ppm.  The advantage of GC-µECD is obvious; the ability of N2O to absorb emitted high energy electrons increases sensitivity for this compound down to ppb detection limits.

Alumina columns will absorb CO2, and are extremely sensitive to water.  Absorbed CO2 and water will effect column loading capacity over time.  However, these can be easily removed by conditioning the column at its maximum temperature.

Column: Rt-Alumina BOND/Na2SO4 30m x 0.53mm x 10µm (cat.# 19755); Sample: 0.1-0.5% permanent gas mix with nitrous oxide and C2 hydrocarbons (black overlay); Injection: Inj. Vol.: 100µl, split ratio 10:1; Oven Temp: 40°C Isothermal; Carrier Gas: He, constant flow 4.0 ml/min; Detector: TCD

N2O performance on Molecular Sieve 5A column was unanticipated.  The small, polar molecules of N2O fit well in the pores of 5A zeolite and offer excellent retention for nitrous oxide.  Notice that the temperature of the analysis is 200°C (Isothermal).  This is the maximum temperature where carbon monoxide is still separated from methane, and oxygen and nitrogen are baseline resolved under the analysis conditions. And, the unpredictable part, at that temperature N2O requires almost 6 minutes to elute from the column.

Column: Rt-Msieve 5A 30m x 0.53mm x 50µm (cat.#19723); Sample: 0.1-0.5% permanent gas mix with nitrous oxide; Injection: Inj. Vol.: 200µl, split ratio 10:1; Oven Temp: 200°C Isothermal; Carrier Gas: He, constant flow 4 ml/min; Detector: TCD

ShinCarbon columns are not available as capillary columns, however, I wouldn’t be able to complete the overview without showing this analysis using porous carbon material.  The analysis was performed at 165°C, although starting with a lower oven temperature is an option if oxygen and nitrogen must be separated.  ShinCarbon columns are available with 0.53mm ID and can be used with capillary inlets.  The micro-packed option requires Micropacked Inlet Conversion Kits that quickly convert your capillary inlet to an inlet for micropacked columns.  Or, micropacked columns can also simply be installed using “pigtails”.

Column: ShinCarbon ST 2m x 1.0mm 100/120 mesh (cat.# 19808); Sample: 0.1-0.5% permanent gas mix with nitrous oxide and C2 hydrocarbons; Injection: Inj. Vol.: 200µl, split ratio 10:1, Oven Temp: 165°C Isothermal; Carrier Gas: He, constant flow 15 ml/min; Detector: TCD; Notes: Resolution between CO2 and N2O is great enough that overloading the column will not affect quantification of nitrous oxide.

In summary, N2O will separate well from all the permanent gases using any of the above mentioned columns.  The concentrations in most of the samples we are analyzing are very low and require very sensitive detectors and large injection volumes. Next time I will focus on exploring limits of detection using a capillary column and a µECD (required injection volume, and split ratios used).

Literature:
[1] https://doi.org/10.1016/j.trac.2013.11.004
[2] https://doi.org/10.1016/j.jchromb.2014.12.034

What’s That Smell? Odor Analysis with Raptor Biphenyl

 

A wide variety of chemicals are used in the production of consumer goods, and most of them have odors that are released into the atmosphere and/or linger on the final product.   Everyone gets really excited about “new car smell,” but sometimes residual odors on fabric or plastic are off-putting. I noticed that the knock-off replacement FitBit bands were a lot smellier than the original, and it took a while for the plastic-y smell to fade. Specific chemicals and intensity levels can trigger nausea or headaches in sensitive individuals.

Regulations vary around the world for testing parameters, but some compounds that recently came to our attention from our office in Japan are six aldehydes specified in the Japanese Offensive Odor Control Law: acetaldehyde, propionaldehyde, n-butryaldehyde, iso-butyraldehyde, n-valeraldehyde and iso-valeraldehyde.  These short chain aldehydes have pungent, offensive odors described as earthy/musty or like rancid butter.

We currently have an application for DNPH derviatized aldehydes and ketones using a Raptor C18 column and our analyte list includes n-butyraldehyde, but the Japanese law calls for the identification of both n-butyraldehyde and iso-butyraldehyde. Our colleagues in Japan worked with one of their chemical testing customers who kindly provided these chromatograms showing that n- and iso-butyraldehyde can be separated with a Raptor Biphenyl column and a simple 25:75 water:methanol mobile phase. Run time was also reduced, enabling higher sample throughput. Both columns were 2.7µm particle size, 150 x 4.6mm. Analysis was done on a 600 bar LC system with a flow rate of 1 mL/min, 40C, and UV detection at 360nm.

 

 

 

 

 

 

 

 

 

If you’re doing odor testing in plastic and resin products and need to separate butyraldehyde isomers, give the Raptor Biphenyl a try!

 

 

 

 

FAMEs blog part 4: Struggling with using hydrogen for AOCS methods Ce 1j-07 or Ce 1h-05?

This blog a part of a series: part 1, part 2, and part 3

Recently I came across customers’ issue with AOCS method Ce 1h-05 used with hydrogen as a carrier gas and I’ve decided to look more closely into what conditions are suggested for this analysis. While at it, I looked also into conditions of methods Ce 1j-07 (AOCS) and AOAC 996.06. What I’ve noticed at first glance is that these methods are written with helium in mind, however, even when using helium, the flow suggested in the method might not provide the best resolution. The method’s parameters are summarized below:

Table 1: Summary of method parameters

What I highlighted in the table are the suggested linear velocities. As the color-coding suggests, 3 out of 5 linear velocities are completely outside of the optimal range. The optimal linear velocity (according to van Deemter) is ~ 25 cm/sec for He and ~ 40-50 for H2. This means that we can speed up the analysis and gain efficiency! Read the rest of this entry »

FAMEs blog part 3: If I Use a Rt-2560 with my GC-MS will it explode?

This blog a part of a series: part 1, part 2, and part 4

Disclaimer: Do not use non-bonded columns, such as Rt-2560, in GC-MS for routine analysis! If you have the need to run some samples, here is what to expect (i.e. quite a bit of bleed)

In my last blog, I talked about how exciting it was to finally test our columns with a sample containing all kinds of trans-fatty acids. The Rt-2560 provided the best separation of C18:1 isomers.  At first, I was having doubts about the identity of the peaks that didn’t align with the cis/trans standard, marked by a purple star in the chromatogram (Fig. 1).

Fig 1: Separation of C18:1 isomers in frosting using GC-FID on Rt-2560. The red trace is the frosting sample, blue trace is the cis/trans standard. Purple stars mark unidentified peaks.

The obvious course of action is to run the sample with GC-MS, however, the Rt-2560 is not bonded and using other columns is out of the question since the elution order is completely different.  As I mentioned above, Rt-2560 is not recommended for use with MS detector due to its high bleed, but on the other hand, it is a fast way to tentative identification. Read the rest of this entry »