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 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

http://www.restek.com/Landing-Pages/Content/gen_B007

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 – https://www.restek.com/Technical-Resources/Technical-Library/General-Interest/general_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

Applications

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:

Environmental

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

Petro

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

Others

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

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

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

Pro-EZGC

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:

http://www.restek.com/ezgc

 

 

 

 

 

 

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 »

What’s in a name? A C18 by any other name would not be the ARC-18

You have probably read or been told numerous times and in numerous ways that not all C18 columns are the same. And that is very true. Particle morphology, bonding chemistry, and add-ons like end capping all influence the retention and selectivity of this workhorse LC phase. At Restek we have an interesting C18 phase that we call the ARC-18 that I would like extol upon if I may.

The name ARC-18 is descriptive of one of its most useful characteristics. I actually had the pleasure of coming up with this name (a love/hate task for any product manager). The “AR” in ARC-18 stands for “Acid Resistant” which is very descriptive of this C18 phase. Through steric hindrance or the add on of bulky side groups near the ligand connection to the silica the bond is protected from the attack of acidic mobile phases that can cleave off the C18 and cause your columns to lose retention.

 

The acid resistance of a sterically protected C18 is well documented. We often describe this in comparison to non-protected C18s. And its advantages are highly sought after. Especially when you want a long lasting and stable column for LC-MS/MS where the mobile phases are typically acidic. An area where that is particularly important is in the analysis of peptides. My colleagues here at Restek did some fantastic research to demonstrate how the acid resistance of the ARC-18 allows for the flexibility of acidic adjustments to optimize peptide analysis.   http://www.restek.com/pdfs/PHAN2615-UNV.pdf

While there are other sterically protected C18s on the market you may find that these phases are also end capped. Encapping is typically done to prevent analyte interaction with the silica surface which can cause secondary retention exhibited as peak tailing. We found that C18s that were both sterically hindered and end capped (e.g. TMS) could take longer to equilibrate and therefore increase your run time. The endcapping can also cause the peak shape of some basic compounds to suffer. We wanted a C18 with a well-balanced retention profile for many different types of compounds like pesticide panels.

Another area where this phase shines is in cannabis potency analysis. We have demonstrated excellent LC-UV separation for 16 Cannabinoids on both our Raptor 2.7 (shown below) and 1.8µm columns utilizing the unique selectivity of the ARC-18 phase.

16 Cannabinoids on Raptor 2.7µm ARC-18

So if you need a robust C18 column for LC-MS/MS, a selective column for cannabis potency, a well-balanced C18 for a wide array of pesticides, or a versatile column for peptides, have a look at the ARC-18. It is truly ahead of the curve.

How often do I need to get my electronic flowmeter recalibrated?

The answer is it depends. It depends on how often you use it. It depends on the environment it has been exposed to. It depends on what your company’s, industry’s or government’s regulations on recalibration are. It depends on whether you have accidentally dropped or banged the device. It depends on how confident you are of the results your are getting.

 

 

 

 

 

 

 

 

 

All instruments degrade with time
Most measuring devices drift out of tolerance, and some devices need more frequent calibration than others.  The reasons depend on the technologies used in the device and where the device is being used.  When the device is primarily electronic in nature, the resistors, capacitors, and solid-state components that comprise it will deteriorate with time and exposure to heat, cold, and radiation.  As a result, the accuracy of the measurements made by the device also degrade with time until its specifications are exceeded.  Usually, the calibration process can compensate for this degradation through electrical adjustments to the device.  When calibration cannot bring the instrument back into specification, some repairs or part replacements may be needed.

Restek spent a lot of time developing and testing our Proflow 6000 flowmeter.  Under the controlled lab conditions we subjected our devices to we found that our devices stayed within acceptable calibration ranges for at least a year.  However, not all customers use or store the devices in the same way in which we tested them.  Therefore it is up to customers to determine there own frequency of testing.

When customers return devices for recalibration the collection of as-found data gives a good snapshot of how out of calibration a device is (this data is given in the recalibration certificate).  In most cases one or two calibration points are slightly out of range.  This is a good indication that the device was still providing accurate data up to that date.  If, however, the as found data shows significant drift from the calibration then it is an indication that there is damage to the flow sensor manifold.  In our experience this has occurred from exposure to too high a flow rate, even it if is a short burst (always establish flow before applying the flowmeter to measure the flow), or that the device has been dropped or banged.

To always get the most accurate flow measurements, contact Customer Service to send in your flowmeter for recalibration (cat.# 22656-R).

The Chromatography Picture-Show

If you’re caught up on all your favorite shows, might I suggest the Restek Video Library for your next binge. Most of the episodes only run about two minutes, so there are few extraneous subplots. (And, so far, no car chases. Not a single one in over 50 videos! But new episodes are added all the time, so who knows?)

screen shot showing the library and its menu location

The cast is superb, and delivers performances packed with practical wisdom. Their costumes probably won’t dominate the awards, but the concise and helpful info they’re providing outshines such considerations. Also of note is the use of exotic filming locations such as laboratories and even the abstract realm of cyberspace. You feel like you’re right there. The cinematographer’s boldness is most apparent in the unflinchingly informative depictions of the guts of LC and GC instrumentation.

Diverse plotlines offer something for nearly everyone. From the heartbreak of tailing peaks to the triumph of a clean, square cut on a fused silica column, from the thrill of proper LC column storage to the drama of detector lamp replacement, it’s all there. There’s even a very special episode about finding the reference standards that match your requirements.

Although these gems have yet to show up on any of the major streaming services, they’re easy to track down. You can even use your phone and take them into the lab with you. Here’s the hookup:

http://www.restek.com/Technical-Resources/Technical-Library/Video-Library

https://www.youtube.com/user/RestekCorp