Archive for the ‘Miscellaneous’ Category

Think twice before purchasing a 3/16” OD packed column

So you may be asking yourself, why the cautionary statement? Well, it’s very simple, many of our customers who purchase 3/16” OD (outside diameter) packed columns have a difficult time installing them into their GC oven.  Why?  Sometimes finding the appropriate fitting/ferrule is difficult.

Let’s say you have a packed column instrument. If your injection port was designed for 1/4” OD columns, then installation is usually not an issue.  Most customers can use a 1/4” x 3/16” OD reducing ferrule, like Restek 20258. To center the column properly (which is recommended if you plan to inject your sample into the packed column) and if you have an Agilent GC with a packed column injection port, you can use our kit 21650, which resembles what is shown in the photo below.  The silver thing that looks like a GC injection port liner is called a “centering sleeve”, and as you may guess, its purpose is to center the packed column in the injection port.

21650

 

Now let’s look at a few scenarios where installing a 3/16” OD packed column is not so simple. Many modern GC’s have injection ports designed for 1/8” packed columns.  So how does one install the larger 3/16” OD packed column into this smaller injection port?  You will need a short piece of 1/8” OD tubing and a 3/16” to 1/8” reducing compression (straight) union like Swagelok SS-300-6-2. Unfortunately, we do not sell this fitting.  However, we do sell a 1/4” x 1/8” reducing union, Restek 23170.  Simply replace the 1/4” metal ferrule set with ferrule 20258.

What if you have a GC designed for only capillary columns? Normally we would recommend a “pigtail” set-up, like described in this FAQ.  How do I install a packed column into a capillary GC injection port?  However, you would need a 3/16” x 1/16” reducing (straight) union, like Swagelok SS-300-6-1. Unfortunately, we do not sell this fitting either.  However, we do sell a 1/4” x 1/16” reducing union, Restek 23169.  Simply replace the 1/4” metal ferrule set with ferrule 20258.

In summary, before purchasing a 3/16” OD packed column, make sure you have the proper fittings/ferrules available for installation. I briefly mentioned this in my post titled Things to Consider Before Ordering a Packed Column.  To save yourself frustration, do a little homework first to determine if a 3/16” OD column is really your best choice, and if not, consider an alternative OD based upon your particular instrument.

 

Pesticides/Fungicide cocktails responsible for Death of Bees: analysis via GC-MS

 

2011-jaap-pasfoto4-smallResearchers at the University of Maryland and the US Department of agriculture may have uncovered the mystery of high mortality in honeybees. These insects are responsible for pollinating over 130 different crops in the US alone. Loss of this pollinator species could cost the US $15 Billion annually. The EU (European Union) issued a temporary ban against the neonicotinoid pesticides. Honeybee deaths may be caused by  a ‘witches brew’ of pesticides and antifungals.

 

The scientists are narrowing down which pesticides and antifungals (fungicides) impairs the bees by investigating pollen of different crops (almonds, apple, cranberry, watermelon, pumpkin, cucumber and blueberries). Since a different cocktail of pesticides is used on varying crops researchers have the ability to determine which pesticides have the greatest effect on bee mortality.

On average crops were sprayed with nine different pesticides and one crop tested had 21 different pesticides present. The combination of these chemicals reduces the bees’ resistance to the parasite Nosema ceranae. Bees with compromised resistance die. Some of the most notable pesticides were chlorothalonil, pyraclostrobin (fungicides) and fluvalinate, amitraz (insecticides). This research was published in the scientific journal PLOS One.

Chlorothalonil is analyzed by GC and can be performed on a non-polar Rxi-5ms type column or a stabilized Rxi-5Sil MS. For a list of applications see:
http://www.restek.com/chromatogram/search?s=type:GC::chlorothalonil

Insecticide Fluvalinate and pyraclostrobin fungicides, are a bit more challenging:
http://www.restek.com/chromatogram/search?s=type:GC::chlorothalonil::fluvalinate

We have done this one only using comprehensive (GCxGC-TOF). Here Chlorothanil is also determined. Fig 1 shows a typical chromatogram. In the second dimension the Rtx-200 was chosen showing very good separation of peaks of interest over the whole separation space.

fig. 1 pesticides GCxGC

Fig 1: separation of pesticides using GCxGC-TOF, 30m x 0.25mm Rxi-5SilMS in first dimension and Rtx-200 in second dimension

What are these O-rings for that I received with my baseplate trap?

Some of you have noticed that included with several of our baseplate traps are a package of two small O-rings. Technical Service has been informed that these are the O-rings which fit onto the check valves on your baseplate (see red arrows below).  Does this mean that you need to replace these O-rings?  Not necessarily.  Carefully inspect the O-rings on the check valves, and if you do not see any signs of wear (cracks, deformation, etc…), you probably don’t need to replace them.  However, if they do exhibit signs of wear, go ahead and replace them.

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 Baseplate 4

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If you also need the larger O-rings that are located on the baseplate, at the base of the check valves (as identified by the green arrows), you can obtain those by purchasing Restek catalog number 22023.

22023

Which GC injection port liner to use for gas samples

The answer seems fairly straightforward: Use a narrow internal diameter (ID) liner to keep peak shapes sharp by preventing band broadening; but this isn’t always the correct answer. There has to be enough internal volume in the liner to contain all of the sample.  Let me explain.

Let’s first look at liners when using purge & trap (P&T). All instrumentation that I am familiar with uses a transfer line from the P&T unit to the GC injection port.  In this case, you do want to use a narrow ID liner to minimize dead volume and prevent band broadening, especially for the compounds which will not condense and refocus within the capillary column.

Now let’s look at liners when using headspace (HS). Headspace units can transfer the sample to the injection port two ways:

(1) Using a transfer line (like those used on a P&T unit).

(2) Using a Gas-Tight syringe.

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If the headspace unit uses a transfer line, then a small ID liner should be used. However, if a Gas-Tight syringe is used to inject the gas sample directly into an injection port liner, then a larger ID liner is commonly used.  I briefly discussed liner selection for gas samples in the post below.

Liners Every Lab Should Own (in my opinion)

In this post, I stated:

The liner below is Restek 23302.1 Sky® 4.0mm ID Single Taper Inlet Liner , which is typically the best choice for 1-2µL injections of non-polar solvents (like hexane), 0.5-1µL injections of polar solvents (like methanol), and gas injections approximately > 250µL to 1mL.

SG4mmID

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The liner below is Restek 23315.1 Sky® 2.0mm ID Single Taper Inlet Liner , which is typically the best choice for 1µL or less injections of non-polar solvents (with low expansion volumes), or gas injections less than approximately 250µL.

SG2mmID

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Note:  The liners above are typically used for splitless (or split/splitless) injections.  If you are splitting your sample, choose an open-bottom liner (with no gooseneck or other restriction at the bottom), like 23301.1 or 23333.1 (shown below).

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.Sky® 4.0 mm ID Straight Inlet Liner  (23303.1)

23301_1_ph_co_lnr

 

If you are not using a syringe for sample introduction, but instead the sample is from a purge & trap unit or gas sampling valve, then the liner I usually recommend is 23333.1 (photo below).  Sky® 1.0mm ID Straight Inlet Liner

1mmID

 

Please note that these are representative liners for an Agilent GC with a split/splitless injection port; the catalog number of the liner you would select depends upon your specific instrument and injection port.

 

In summary, liner selection for gas samples will depend on your particular instrumentation and how the sample is introduced into the injection port liner. If your instrument uses a transfer line, then a small ID liner will likely provide you the best chromatography.  If a Gas-Tight syringe is used to inject the gas sample, a larger internal diameter liner will usually provide you the best results.

Electronic Cigarettes Part IV: Solution Analysis – So what is REALLY in the e-juice?

Okay… so time to bring this story full circle. Recall in our first e-cigarette blog we demonstrated a quick proof of concept for analyzing the major constituents of e-juice on a GC-MS. Next in part II we demonstrated some faster capabilities on a GC-FID and even threw in a calibration curve. Then in our most recent post we showed you how our EZGC Method Translator and Flow Calculator could be used to easily switch from helium to hydrogen carrier gas for working on electronic cigarette solutions. NOW… time for us to pull back the curtain on what we can really see in in the e-juice.

So we took our GC-MS method from part I and slowed down the oven to near OHR @ 11 °C/min. No rush right now, time to carefully dissect the e-juice. We also dropped our split from 200:1 down to 10:1. Lastly, we decreased our dilution from 100:1 down to 2:1, just so we had enough methylene chloride in the sample to cut the viscosity. Here is what it looks like:

E-Juice Minor 3

Not exactly anything to get too excited about, right!? Heck… we have seen the propylene glycol, glycerin, and nicotine peaks enough by now that you should be bored. Not to mention that the peak shape looks horrible due to the overloading situation created by the minimal dilution and split ratio. But wait just a minute… lets zoom in on the above chromatogram and really take a look:

 

E-Juice Minor Zoom ABAM!!! Not just the propylene glycol, glycerin, and nicotine we’ve been talking about all along! Based on the above chromatogram, our e-juice has a lot more constituents than that. So what are all of these peaks? Well… the following chromatogram will hopefully help break down all the unknown compounds into several more digestible sections:

E-Juice Minor Zoom A3

So as you may see in the above chromatogram, we have broken everything down into 5 different sections. You may also see in the table below, we have a list of the tentatively identified/unidentified compounds. Note: We only included compounds with a mass spectral quality of 80% or greater according to the NIST 2005 database. Compounds with 100% quality have been confirmed with standards.

E-Juice List B

38 [45 minus the 7 present in a solvent blank (see chromatogram below)] compounds in this e-juice. Some of which we were able to tentatively identify and some of which have even been confirmed with standards. So what does this all mean? Well…we will have to save that discussion for a later date, as this blog has now approached my maximum allowable length. In the meantime you may draw your own conclusions, but until then… stay tuned!

E-Juice Solvent Blank

Summer Vacation: Newport Naval Superfund Site

Weaver Cove off of Defense Highway (Burma Road) looking north to Carr Point in the direction of Derecktor Shipyard

Weaver Cove off of Defense Highway (Burma Road) looking south to Carr Point in the direction of Derecktor Shipyard

This is a continuation of my summer series for fun places to visit that also provide a glimpse into the history of chemical waste in America. In our first installment of summer vacations we were headed to Niagara Falls, New York and stopped along the way to visit Love Canal; probably the most well-known hazardous waste tragedy in the country and the impetus for many of the EPA methods we use today. Years later while vacationing along the beaches of Rhode Island I stumbled across a sign (figure 1). A quick internet search revealed the Newport Naval Education / Training Center Superfund site (NETC).

Superfund, also known as the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) was enacted by the US federal government in response to national hazardous waste disasters that garnered significant public attention; most notably Love Canal. The Environmental Protection Agency (EPA) was given control over enforcement with the following stated regulatory actions:

  1. Determine methods for discovering and investigating facilities where hazardous substances have been disposed
  2. Methods for evaluating substantial danger to public health
  3. Measures for removal and remedy
  4. Effective plan for local, state and federal agencies
  5. Effective response equipment for accidental discharge
  6. Assignment of responsibility
  7. Evaluate cost effective plans for remediation
  8. Prioritize Superfund sites
  9. Roles for private organizations in testing & cleanup
  10. Standards and testing procedures
Figure 1: Entrance to Tank Farm #1 at NETC

Figure 1: Entrance to Tank Farm #1 at NETC

The EPA prioritized toxic waste areas using a scoring system based on risk to human health and determined funding for these sites under the National Priorities List (NPL). As of August 15th, 2014 the NETC and 1317 other contaminated sites are listed and require cleanup, monitoring or further investigation. This week the EPA approved a $21 million cleanup for NETC which will be paid for by the US Navy.

Additional Reading:

CERCLA Section 105 page 536

EPA Reports: Newport Naval Education and Training Center

Superfund Cleanup to Cost $20 Million

Dredging at the Derecktor Shipyard

Need help in selecting replacement weldments and shell weldments for your Agilent 5890/6850/6890 GC?

When you need a replacement weldment and/or shell weldment for your Agilent 5890/6850/6890 GC, we have the parts. However, selecting the correct catalog numbers can be a little confusing for many of us.  As a result, I decided to try and simplify the selection process below.  I hope you find it helpful.

 

5890 Weldment catalog numbers are 20265 for stainless and 20267 for Siltek –Treated.

20265

 20265

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5890 Shell Weldment catalog numbers are 20266 for stainless and 20268 for Siltek-Treated.

20266

 20266

 

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6850 & 6890 Weldment:  If your GC has one of the split vent traps shown below (Restek kit 23031, commonly called large canister filter),

23031

 23031

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and your instrument does have electronic pressure control (EPC), then the associated Restek weldment replacements are 22686 for stainless and 22670 for Siltek-Treated.

22686

 22686

 

If your 6850 and/or 6890 GC has a split vent trap like shown below (Restek 22820, sometimes called a split vent pencil trap or chemical trap),

22820

 22820

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and your 6850 and/or 6890 does not have EPC, then the weldment catalog numbers are 20265 for stainless and 20267 for Siltek-Treated.  Please note that these are the same weldments used on the 5890 injection ports.

 

If your 6850 and/or 6890 GC has a split vent trap like shown above (Restek 22820), but it does have EPC, then the Restek weldment replacements are 22674 for stainless and 22672 for Siltek-Treated.

22674

 22674

 

6850 & 6890 Shell Weldment catalog numbers are 22673 for stainless and 22671 for Siltek-Treated.

22673

 22673

Electronic Cigarettes Part III: We’re gonna vape on the EZGC bandwagon.

band-wagon

The title says it all… we’re taking our e-cig method and jumping on the EZGC Method Translator and Flow Calculator bandwagon. Why… well because all the cool kids are doing it. No seriously… to simply reiterate how easy it is to use the Method Translator. In fact, the EZGC Method Translator makes life so easy you can kick back, put your feet up, and vape away on an e-cig. Okay, so maybe we do not endorse such behavior, but you get the point!

So we (Amanda, Colton, and me) took our e-cig solution analysis method and used the method translator to switch from helium to hydrogen carrier gas. It was as simple as plugging in our current method parameters (which you may find in part II of this blog series) and then letting the translator do the work. As you will see below, the flow bumped up to 2.5 mL/min and the oven ramping jumped to 54 °C/min. All of this correlates to our 4.84 min run dropping down to a mere 3.11 min. But most important… we no longer use helium!

EZGC

 

Now let’s take a look at how this… well… looks!

E-Cigs Part III C-Gram I

Pretty nice, but let’s compare this to our previous method. The following overlay will show you the difference between the “old” helium (blue trace) and “new” hydrogen (red trace) carrier gas methods:

E-Cigs Part III C-Gram II

 

Now let’s look at this from a different angle. Here the overlay has taken into account the off-set due to hydrogen being faster:

E-Cigs Part III C-Gram IIB

Once again, looking good! Now I know some of you may be saying… “what the heck is this guy thinking; I can’t ramp at 54 °C/min… expletive!!!”… Which is certainly a fair statement, minus the expletive. We just want to demonstrate what you may achieve with a fast-ramping oven like we have. So for the rest of you… our original 35 °C/min ramping method should work well. So let’s just capitalize on the hydrogen like so:

E-Cigs Part III C-Gram III

Even with the slower oven rate, the hydrogen method gets our compounds eluted a minute faster. The problem is that we left an extra minute hanging out there in no-mans-land. So we can recoup that minute by simply dropping the final oven temperature from 260 to 240 °C like so:

E-Cigs Part III C-Gram IV

So there you have it… several hydrogen-based methods for the analysis of electronic cigarette solution. Regardless of which method you chose… the EZGC Method Translator and Flow Calculator made for a simple transition between helium and hydrogen carrier gas. I literally ran all 4 chromatograms (yes, I know there are technically 5, but there was a duplicate in there) back-to-back as you see above… with no “trial and error” or “guess and check”. Now we have a shorter run, with super crisp peaks, and no helium consumption. The problem is… I now have to figure out what to do with all this extra time!?!?

 

 

Electronic Cigarettes Part II: Solution Analysis – You don’t have an MS… no problem.

In the last e-cigarette blog we (Amanda, Colton, and me) showed you a quick proof of concept for analyzing the major constituents of e-juice. Working from that starting point, we realized that some labs may not have access to a GC-MS and/or some may only be interested in a very quick screening method for the nicotine content in e-juice. So…  that is exactly what we’re showing you today.

The table below contains all the specifics of interest for a rapid GC-FID screening method for nicotine in e-juice.

GC-FID Parameters D

We continue to use our thick film volatiles column, because the ultimate goal with e-smokes is to see what is in the vapor. Also, it is already doing an excellent job on the current application. So we simply bumped up our starting temp to 100 and now we have a 5 minute run (see below).

GC-FIDOkay… so there may be a little bit more. As we mentioned last time, we purchased some raw e-juice and analyzed it as is (i.e., straight from the refill bottle). Well since the last blog we have learned that the e-juice is extremely viscous. If you plan to analyze the e-juice raw (i.e., without any dilutions) you will have to set up your injector appropriately (see below). We suggest you include at least one sample wash; lower the sample wash speed down to ~30 µL/min; and you may also want to add in a viscosity delay. Close observation of your autosampler syringe coupled with a little experimentation will get you to where you need.

GC-FID B

Alternatively, you could just simply dilute your e-juice, which is ultimately what we suggest. If you want to have quantitative nicotine results, clearly you will need to calibrate your instrument. So when you use our nicotine standard at 1,000 µg/mL you will realize that most of e-juice nicotine concentrations are well above this. So… a nice 100 fold dilution with methylene chloride (yes, methylene chloride and not methanol if you want to look at ethanol) will kill the following two birds with one stone: 1. you no longer have viscosity issues. 2. your concentrations fall nicely into your calibration curve.

Speaking of which… the aforementioned method calibrates fairly well [i.e., the correlation coefficient (r) (not the coefficient of determination (r²)) = 0.99562] from 1.6 x 10-2 to 1.0 mg/mL (see below). FYI – most e-juice nicotine concentrations are ~10 to 20 mg/mL for a 1.8% nicotine solution. Remember… we diluted by 100 fold, so we typically injected 0.1 to 0.2 mg/mL. Well within the aforementioned calibration curve.

E-Cigs CalibraitonSo… that’s enough about e-cigs for one week. But stay tuned for the next blog on electronic cigarettes.

Book Review: Echoes of Life: What Fossil Molecules Reveal about Earth History.

The year 1936 marks the beginning of organic geochemistry. It started with Alfred Treibs’ discovery of porphyrins in petroleum; compounds that closely resemble chlorophylls in plant matter. Another 25 years would pass before scientists recognized that these compounds, known as biomarkers, could reveal insights into the evolution of plants and animals spanning a time frame measured in billions of years.

The striking similarities between cholesterol and sterane.

The striking similarities between cholesterol and sterane.

Echoes of Life weaves a complex fabric of stories, peppered with personal details, that describe the emergence of analytical techniques; mainly GC-MS. The authors are a mix of organic geochemist, founding father of biomarker research and a marine chemist/novelist that draw on a variety of perspectives and experiences. Echoes of Life is a well written, digestible story rather than a textbook.  One of its enduring facets is the ability to eloquently describe the required transition of geochemist to analytical chemist; a necessity to crack the origins of oil. The book starts as a disjointed collection of stories from finding “life” on the moon to botanists studying leaf waxes. Using mass spectral interpretation it was evident that cholesterol could be found in oil in the modified form of steranes and hopanes. They were “stripped of their double bonds and oxygen containing functional groups reduced to their bare carbon skeletons.” The book follows researchers from around the world arriving at the same conclusion from various fields using different techniques. Described as, “a tribe of scattered chemists using the new technique of ‘coupled GC-MS’ and coming to the same conclusion.”

The Deep Sea Drilling Project (DSDP) revealed chemical traces of algae, zooplankton and microbes that proved to be a chemical chronicle of the last 150 million years. The keys to understanding the history of earth, its climate and life were locked in these biomarkers. For instance the degree of unsaturation in algae’s lipids increased systematically with an increase in temperature. Dialkyl ketones containing 37 to 39 carbon atoms were analyzed to determine the number of double bonds remaining. Combining age of sediment and dialkyl ketone data, scientists were able to estimate regional global temperatures.

Sterane and Hopane patterns (shaded areas) by GC-MS SIM using an Rxi-5Sil MS 30m x 0.25mm x 1.0µm film column.

Sterane and Hopane patterns in MC252 Crude (shaded areas) by GC-MS SIM using an Rxi-5Sil MS 30m x 0.25mm x 0.25µm film column.

The story is a combination of thousands of scientific papers, hundreds of interviews and many anecdotes as a mechanism for moving the story forward. Reflected in these pages is an insatiable curiosity that defines science. This book is a journey of discovery, the human spirit and the quest to understand our surroundings. It is a trip worth taking.

Echoes of Life: What Fossil Molecules Reveal about Earth History. Susan M. Gaines, Geoffrey Eglinton and Jurgen Rullkotter. Oxford University Press, 2008. 376 pp. (ISBN 9780195176193 cloth).

Check out Michelle’s work on oil identification: Fingerprinting Crude Oils and Tarballs using Biomarkers and Comprehensive Two-Dimensional Gas Chromatography

Petroleum Biomarkers and Tarballs at the 36th International Symposium on Capillary Chromatography and the 9th GCxGC Symposium

Gulf Oil Spill Blogs

http://blog.restek.com/?cat=3