Split Injection GC: Increasing Response Factors for Compounds Prone to Inlet Liner Adsorption by Using Shoot-and-Dilute GC

Author: Jack Cochran

Published By: LCGC Chromatography Online

Issue: Volume 12, Issue 16

Year of Publication: 2016

Link: http://www.chromatographyonline.com/split-injection-gc-increasing-response-factors-compounds-prone-inlet-liner-adsorption-using-shoot–0

 

Abstract:

Hopefully, by now at least, readers who are following this Practical GC series on split injection gas chromatography (GC) (1–3) have been able to take advantage of its benefits in their own laboratories. Chemists analyzing environmental samples, especially those that produce dirty extracts, could have the most to gain from split injection GC given the wide variety of semivolatile organic compounds that are typically determined. Analyte lists include compounds that can react with GC inlet liner surfaces during splitless injection, leading to degradation of those compounds, which prohibits their accurate quantification. In fact, an example was given in my first Practical GC article in The Column (1) for the pesticides endrin and DDT. Sample extracts containing high concentrations of involatile material exacerbate the situation because the nonvolatiles are deposited on the inlet liner wool and bottom seal where they catalyze degradation of sensitive compounds. Buildup of nonvolatile material in the inlet during repeated splitless injections leads to even higher breakdown. Split injection mitigates the degradation potential because the typical inlet flow is 10 times (or more) higher than for splitless injection. The time for unwanted reactions on liner surfaces, including those that have been modified by nonvolatile coextractives, is reduced in split injection.

Analysis of Gases via Gas Chromatography: Part 3: CO and CO2

Author: Jaap de Zeeuw
Restek Corporation

Published By:  J. Sep. Sci.

Year of Publication: 2016

Abstract:

CO and CO2 are products that are present in many industrial processes. CO2 is used in many applications varying from propellants, refrigerants, preservatives, beverages, inert atmosphere, and fire extinguishers. It’s also used in oil recovery, supercritical solvent, and greenhouse analysis. Carbon dioxide is analyzed typically at higher levels (10 ppm – % level). CO is a toxic gas, but it is used mostly used as chemical precursor. Both CO and CO2 are analyzed at levels from 100 ppb to % level. Because these gases cannot be detected by FID, other detectors are required. One can also convert the CO/CO2 into methane to take advantage of FID sensitivity.

Analysis of Gases via Gas Chromatography: Part 2: Sulfur Gases

Author: Jaap de Zeeuw
Restek Corporation

Published By:  J. Sep. Sci.

Year of Publication: 2016

Abstract:

Sulfur components are widely present in many raw materials used for hydrocarbon processing. The sulfur components are undesirable because they have a strong smell, they cause acidic rain, they poison (expensive) catalysts and reduce polymer yields. Most problematic sulfur gases are hydrogen sulfide (H2S), carbonyl sulfide (COS) and methyl-ethyl mercaptans. These compounds have to be measured at ppb levels. Besides that sulfur gases are volatile, they are also are very reactive. Systems for trace sulfur analysis must be very inert from the sampling device to GC setup to measure reproducible values at ppb levels.

Split Injection GC: Setting the Split Ratio in Shoot-and-Dilute GC

Author(s): Jack Cochran
Restek Corporation

Published By: LCGC’s The Column

Issue: Volume 12, Issue 8

Year of Publication: 2016

Link: http://www.chromatographyonline.com/split-injection-gc-setting-split-ratio-shoot-and-dilute-gc

For the full issue,visit http://images2.advanstar.com/PixelMags/lctc/digitaledition/May06-2016-us.html#11

Abstract: Jack Cochran’s new column “Practical GC” provides readers with practical advice and new experimental evidence for how to get the best results from their gas chromatography (GC) systems.  This installment looks at understanding and using split ratio for “shoot and dilute” GC.

Analysis of Gases via Gas Chromatography: Part 1: Nitrous Oxide

Author: Jaap de Zeeuw
Restek Corporation

Published By:  J. Sep. Sci.

Year of Publication: 2016

Abstract:

Gas chromatography (GC) is a technique that deals with gas separations. Practically the components to separate must be brought in the gaseous phase to be able to be transported by the carrier gas. In order to do that, the temperature of the sample and column can be increased. Today’s gas chromatographs can be used up to 500 °C, meaning that it is possible to analyse components with boiling points around 700 °C. The component must be thermally stable. This works fine for hydrocarbons but more polar molecules will decompose.

Faster (GC) Tactics: Five ways to speed up gas chromatography analyses using your current system

Author: Jaap de Zeeuw
Restek Corporation

Published By: The Analytical Scientist

Issue: 36

Year of Publication: 2016

Link: https://theanalyticalscientist.com/issues/the-new-dawn-of-precision-medicine/polishing-your-injection-technique

For the full issue, visit: https://theanalyticalscientist.com/fileadmin/tas/pdf-versions/TAS-Issue-0116.pdf

Abstract:

Reducing analysis time is a constant priority. And it’s sensible because it cuts costs per analysis and you get faster results. Here, I’d like to share some clever ways to reduce gas chromatography (GC) analysis time using existing instrumentation in two real-world situations.

Split Injection GC: The Benefits of “Shoot-and-Dilute” GC

Author(s): Jack Cochran
Restek Corporation

Published By: LCGC’s The Column

Issue: Volume 11, Issue 21

Year of Publication: 2015

Link: http://www.chromatographyonline.com/split-injection-gc-benefits-shoot-and-dilute-gc

For the full issue, visit http://images2.advanstar.com/PixelMags/lctc/digitaledition/November23-2015-uk.html

Abstract: Jack Cochran’s new column “Practical GC” aims to provide readers with practical advice and new experimental evidence for how to get the best results from their gas chromatography (GC) systems. The first article in a series on split injection GC focuses on the advantages of using “shoot-and-dilute” GC.

Attend Restek’s Vendor Seminar on GC-MS/MS Performance at RAFA 2015

In addition to exhibiting, Restek will hold a vendor seminar at the 7th International Symposium on Recent Advances in Food Analysis (RAFA). Presented by Restek’s own Julie Kowalski on November 5 at 1:30 p.m., this valuable seminar will explore prolonging GC-MS/MS performance by means of Shoot-and-Dilute injection versus analyte protectants. Prizes will also be given away to select attendees.

RAFA 2015 takes place on November 3–6, 2015 at the Clarion Congress Hotel Prague, Czech Republic. This biennial symposium summarizes the latest strategies and identifies current issues surrounding food quality and safety control analysis and bioanalysis. While at RAFA, be sure to also stop by Booth# 46 for a visit and to discuss our latest innovations in food science.

Visit http://www.rafa2015.eu/programme_vendors_seminars.html today to register for the symposium and to sign up for Restek’s vendor seminar.

Prolonging GC-MS/MS Performance: Shoot-and-Dilute Injection versus Analyte Protectants

Thursday, November 5, 1:30 p.m.
Julie Kowalski and Jack Cochran
Restek Corporation

In gas chromatography–mass spectrometry (GC-MS), most problems occur on the front end, at the GC inlet, where compounds can degrade during hot splitless injection, active compounds can be irreversibly adsorbed to inlet liner surfaces, and nonvolatile material from dirty samples can compromise the transfer of less volatile compounds of interest from the inlet to the GC column. These issues are magnified due to the very slow inlet flow during splitless injection, which is typically less than 2 mL/min.

Two strategies to mitigate these issues will be demonstrated in this seminar. One approach is to use split injection, what we call, and “Shoot-and-Dilute.” With newer, more sensitive GC-MS/MS systems, LOD and LOQ requirements are often achievable using split injections at ratios of 10:1 or greater. Increased flow through the inlet during split injection minimizes residence time inside the inlet liner, which decreases compound degradation and adsorption, and maintains acceptable data quality longer. In addition, GC oven start temperature can be higher, thus reducing overall run time as well as the time needed to re-equilibrate the GC oven prior to the next analysis. Another benefit of split injection is improved peak shape for early eluting pesticides when injecting acetonitrile-based QuEChERS extracts.

The second strategy to overcome GC inlet problems is to use “analyte protectants,” which are essentially volatile and chromatograph-able masking agents such as sugars, diols, etc., that are co-injected with each sample and standard to temporarily occupy active sites in the GC inlet liner and column. These analyte protectants have low m/z ions and the mass spectrometer can essentially overlook them in favor of target compounds.

Both strategies were tested with multiclass pesticides and compared against a typical splitless injection method without use of analyte protectants for QuEChERS samples. For Shoot-and-Dilute, viability of split injection based on detectability of a wide range of analytes was determined. Optimized split injection, inlet, and initial GC oven temperatures were determined. Benefits of analyte protectants were evaluated by peak shapes and responses of both well-behaved and problem pesticides. The goal of both Shoot-and-Dilute and analyte protectants approaches is to improve initial and long-term chromatographic performance.

Changing from Helium and Nitrogen While Maintaining Separation Efficiency and Analysis Time

Author(s): Jaap de Zeeuw and Jack Cochran
Restek Corporation

Published By: LCGC’s The Column

Year of Publication: 2015

Link: http://images2.advanstar.com/PixelMags/lctc/digitaledition/October26-2015-us.html#2

Abstract: Most scientists in the world of gas chromatography (GC) will advise you not to use nitrogen because it is considered a “dinosaur” gas and, instead, use helium, which offers shorter analysis time. But, wouldn’t it be very nice if we could make nitrogen work for applications where helium is not an option?

Changing from Helium to Nitrogen and Maintaining the Separation Efficiency in the Same Analysis Time

Author(s): Jaap de Zeeuw and Jack Cochran
Restek Corporation

Published By: Separation Science

Issue: March 2015

Year of Publication: 2015

Link: www.sepscience.com/Information/Archive/All-Articles/3688-/Changing-from-Helium-to-Nitrogen-and-Maintaining-the-Separation-Efficiency-in-the-Same-Analysis-Time?pageNo=1

You can also view a PDF of this article.

Abstract: For several reasons, there is interest in replacing helium with a different carrier gas in gas chromatography. Hydrogen is the obvious choice but there is a concern on safety and reactivity. It is also possible to use nitrogen but this is often not considered because it has a low optimal flow and velocity. Here we will show that it is possible to replace helium for nitrogen as the carrier gas while separation, peak elution order, analysis time, response, and even oven temperature conditions can be kept the same.