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See how the PFAS Delay Column works! Psst.. Do not delay your action, and take a look at this now.

Per- and polyfluorinated alkyl substances (PFAS) analysis usually requires very low level detection (parts per trillion level) in drinking water. The most common problem we run into is that PFAS are everywhere, including our lab and the very instrument (LC-MS/MS) we use to detect those compounds, so having system-related background interference is very common.

There are two tricky parts in identifying the low level background interferences in PFAS analysis.

Firstly, system-generated background interference exists at very low concentrations from components in the LC-MS/MS workflow including the sample collection bottle, mobile phase cap/lining (made of PTFE), solvent inlet tubing (often FEP or PFA), degasser, LC pump parts, even the autosampler vial septa, and they might not be noticed in the early stage of method development when higher sample concentrations are used.

Secondly, there is actually a build-up of the system-generated background interference each time you equilibrate the LC column, meaning the longer you equilibrate the column or leave the LC idle between injections, the more system-generated background interference will show up in your chromatogram! This can be very challenging since it is likely that you did not see the system-related interference earlier during method development, but later when you want to finalize your method you find yourself struggling with the background interference issues and you cannot move to the method validation step when low concentration samples are to be analyzed!

So how do we get our method to report only the PFAS in our samples while eliminating low level system-generated interferences? We can trap these interferences by using the PFAS Delay Column (27854) before the injector: PFAS in the sample elute in their normal retention window while system-related PFAS elute later as a fairly broad “peak”.

See for yourself in the short 2 min video below, then head over to the PFAS Delay Column (27854) to make your interferences go away. This video is to demonstrate how delay column works for accurate PFAS analysis. Stay tuned for the next blog with chromatograms showing delayed interference “peak”.

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).

[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 these 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 describe 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 »

Cannabis Concentrates Part III: A Second Extraction Approach

And we’re back! Previously, we discussed analyzing residual solvents via HS-GC using a gas-tight syringe. If you missed it, be sure to check it out here! Today, we are talking about a sample extraction technique that is less common, but has great capabilities; known as Solid Phase Microextraction (SPME).

SPME is a sampling technique consisting of a fiber, coated with a sorptive phase. When placed into the headspace of a sample, analytes sorb (adsorb or absorb depending on fiber type) onto the fiber, and are desorbed off the fiber in the GC inlet. We have decided to use the SPME Arrow instead of a traditional SPME fiber for this analysis. The SPME Arrow has a much larger sampling volume, but its best attribute is its durability compared to a traditional fiber (see the figure below).  For more information on SPME, be sure to check out Jason Herrington’s blogs here.



When moving from the HS-Syringe method to the HS-SPME method, a couple extraction parameters must be changed. The HS-Syringe performs best under long equilibration times at higher temperatures, whereas the HS-SPME performs best under shorter equilibration times at lower temperatures. We have the data to support this, so check out Chromablography in the future for the proof! These main differences between the HS-Syringe and HS-SPME can be seen in the tables below. The reason for this drastic difference in temperature is if the SPME Arrow is placed in a hot vial, the fibers temperature will rise. The SPME Arrow’s thermally conductive metal core magnifies this problem. Because the fiber is at a hotter than the laboratory atmosphere, the analytes on the fiber will desorb off before the fiber reaches the inlet. Some compounds of interest, like propane and butane, show incredibly low responses using elevated temperatures. By keeping the fiber at a cooler temperature, we are able to keep those analytes on the fiber until it is desorbed in the GC inlet.



The chromatography comparing the HS-Syringe and HS-SPME methods can be seen below.



Notice that the HS-Syringe gives better response for propane, isobutane, and n-butane. You can see the HS-SPME method quickly has excellent recoveries for higher molecular weight compounds. The peaks tail using HS-SPME, but this is a normal result for this type of extraction technology. Overall, things look good on both the HS-Syringe and the HS-SPME Arrow. Stick around for future blogs where we will go into more depth with both techniques!


Are you experiencing helium supply issues and rising costs?

Helium supply issues are nothing new.  At Restek we have been discussing this off and on for years now.  The following articles and information are just a small selection of what is available on our website and our ChromaBLOGraphy, and are there to help you make informed decisions about alternatives to helium, and reduced helium consumption in your lab.

The History of Shortages


Donald Duck voices silent and birthday balloons fall everywhere as helium disappears…

Will We Go Over the “Helium Cliff”?

Alternatives to Helium

For years we have been writing and lecturing about using alternatives gases to helium in gas chromatography:

GC Carrier Gases – Alternatives to Helium

GC carrier gases, do you really have a choice?

Hydrogen as carrier gas: Always available, Cost effective and Fast

Reduce Helium Consumption by Using Nitrogen Purge Gas for VOCs in Drinking Water


Benefits and Considerations of Converting to Hydrogen Carrier Gas – http://www.restek.com/Technical-Resources/Technical-Library/Petroleum-Petrochemical/petro_PCTJ1729-UNV

Gas Generators

If you choose to move away from helium to hydrogen or nitrogen as a carrier gas, or purge gas, then a gas generator would be a great source for a consistent flow of clean gas.  Gas generators have been used for many years for just this purpose.  Yes they can be a high initial capital expense, but they can pay for themselves in as little as one year when you compare how much you would have been paying for helium in bottles.  The modern gas generators have a series of safety devices built into them so that the concerns over using hydrogen, for example, are diminished to a point that it is no more of a problem than any other gas that is used.

Hydrogen as carrier gas: Always available, Cost effective and Fast

Gas Management in Labs – http://www.restek.com/pdfs/GNSS1758A-UNV

Working Safely with Hydrogen as a Carrier Gas – http://www.restek.com/Technical-Resources/Technical-Library/Editorial/editorial_A016

Using Hydrogen for Gas Chromatography – http://www.restek.com/Landing-Pages/Content/gen_B008

Restek’s Selection of Parker Balston Gas Generator – http://www.restek.com/Supplies-Accessories/GC-Accessories/Gas-Generators


I still hear your hesitancy and want to have some convincing evidence about using alternative gases in your applications.  Well luckily for you we have done a lot of work on this, and here are a few examples:


Organochlorine pesticides – http://www.restek.com/pdfs/EVAR1935-UNV.pdf

Organochlorine Pesticides Analyzed by Gas Chromatography – Electron Capture Detector with Hydrogen Carrier Gas and Concurrent Solvent Recondensation – Large Volume Splitless Injection

VOC Analysis: O.I. Analytical Nitrogen Purge Gas Application Note with Restek Rtx-624 GC Column


ASTM D2887 – http://www.restek.com/pdfs/PCAR2320-UNV.pdf

ASTM D7213 – http://www.restek.com/Technical-Resources/Technical-Library/Petroleum-Petrochemical/petro_PCAR2269-UNV

DHA – http://www.restek.com/pdfs/PCAR2891-UNV.pdf


Blood Alcohol – https://blog.restek.com/?p=6374

Cannabinoids – https://blog.restek.com/?p=7704

Fragrances – https://blog.restek.com/?p=13850


You may not be able to find an example of your application in our database, but you can model it using Pro-EZGC.  The Pro-EZGC suite allows you to enter your current conditions and then change certain parameters to translate the method.  These parameters include the carrier gas.  So you can model and improve your analysis before you even start performing experiments and method development on the instrument.  The following link will take you to the Pro-EZGC suite and the tutorials to help you:








Trans fatty acids analysis part 2: Let’s look at actual samples with incurred TFAs

This blog a part of a series: part 1, part 3, and part 4

In my previous blog, I’ve tried and failed to acquire a sample that contained any trans fatty acids (TFAs). While this is a great news for everyone’s health, the scientist in me was somewhat disappointed. That’s why I first decided to cheat a little bit and look at different TFAs – ruminant TFAs. Ruminant TFAs are products of bacterial metabolism of polyunsaturated fatty acids in the rumen of cattle, sheep or goats, contributing up to 6% of total fat.1 They are present in both dairy products and meat. The major difference between artificial and ruminant TFAs is their distribution. Partial hydrogenation produces TFAs with almost Gaussian distribution, with highest abundance for trans-9 C18:1, while ruminant bacteria skews the distribution towards for trans-11 C18:1 (up to 42 wt%, Fig. 1). It’s also noteworthy that trans-C16:1 can contribute up to 20% of ruminant fats but it is not present in partially hydrogenated oils unless they originate in marine oil.1

Figure 1: Distribution of trans-C18:1 isomers. Adapted from Stender et al.1

Read the rest of this entry »