Jaap de Zeeuw
On November 16–17, Separation Science will again host Food Science 2016 in Singapore. This world-class international conference and exhibition covers key food analysis topics including safety, traceability, authenticity, and ingredients analysis. Restek invites you to attend the show at a special discounted rate. In addition to Jaap de Zeeuw’s presentation, you may attend over 30 other talks on food analysis, quality, and safety.
While you’re the Food 2016 conference, be sure to stop by Booth 112 and visit your local Restek representative, Lab Science Solution. There will be games, giveaways, and information on Restek products and solutions!
Wednesday, November 16
Reduce Analysis Time and Optimize GC Separations in Food Analysis, while Maintaining the Same Peak Elution Order: A New Free Software Tool in GC—the EZGC Method Translator
Jaap de Zeeuw, Restek Corporation
In gas chromatography, there is often a need to optimize separations using different column dimensions, linear gas velocities, detectors, or carrier gases. If you want to get the same peak elution order (same chromatogram), you must make sure that the elution temperatures of the components are kept the same. This can only be done by using a different oven temperature program. To calculate this program, there are free calculation programs available on the web. In this course, we will discuss the details of method conversion using Restek’s EZGC method translator so that you get the same chromatograms with the new method. The course will also cover how existing separations can easily be checked and corrected for optimal separation.
Shoot-and-Dilute GC-MS/MS: Use of Split Injection for Pesticide Residue Screening to Prolong GC Inlet Liner and Column Performance
Jaap de Zeeuw, Julie Kowalski, and Jack Cochran, Restek Corporation
Shoot-and-dilute GC-MS/MS uses split injection for GC paired with a very sensitive triple quadrupole mass spectrometer. Split injection can alleviate matrix-related issues that occur at the GC inlet and column. There are well-known problems associated with splitless injection of dirty samples, most notably compound degradation and drastic response changes. This can occur very quickly with real samples, sometimes with a single injection of a particularly dirty sample. Inlet and column maintenance are needed to restore instrument performance resulting in instrument downtime. An easy way to mitigate these problems is to use split injection when possible. That is, if the limit of detection and limit of quantitation requirements are achievable using split injections at ratios of 10:1 or greater. Increased flow through the GC inlet with split injection minimizes residence time inside the inlet liner. This decreases compound degradation and maintains acceptable data quality longer, especially during dirty sample analyses.
In addition to the benefits described above, the GC oven start temperature can be higher, thus reducing overall analysis time as well as the time needed to re-equilibrate the oven. Also, split injection of the common QuEChERS solvent, acetonitrile, is easily accommodated on a nonpolar 5-type GC column, allowing symmetrical peak shapes of early eluting compounds like methamidophos, dichlorvos, and acephate. This eliminates the need for extensive initial oven temperature optimization or time-consuming solvent exchange.
Shoot-and-dilute GC-MS/MS was tested for multiclass pesticides and compared with a splitless injection method. Split injection and the initial GC oven temperature parameters were optimized. Viability of split injection based on detectability of over 200 analytes was determined in QuEChERS-prepared green bell pepper, celery, and orange. Green bell pepper cleanup using dispersive SPE without graphitized carbon black sorbent was less than ideal with a relatively high level of chlorophyll remaining in the sample, which severely stressed GC inlet performance for splitless work while the split method was much more robust. Ruggedness of split and splitless methods was evaluated by comparing average response factors and corresponding %RSDs and by showing chromatographic performance differences, especially for compounds that show degradation products.
Wool Packing or No Wool Packing in a Splitless GC Inlet Liner–Which is better for Pesticide Analysis? A Case Study with a QuEChERS Strawberry Extract
Jaap de Zeeuw and Jack Cochran, Restek Corporation
Pesticide chemists usually avoid glass wool packing for splitless injection GC because sometimes lower responses are seen for active or thermally unstable pesticides (e.g., carbaryl, DDT, iprodione, etc.) However, properly deactivated quartz wool is not only a valuable protector of the GC column from nonvolatile “dirt,” but it also offers increased responses for pesticides because it stops them from hitting the bottom seal in a typical GC inlet where they can be lost or degraded.
This study compared GC-MS response factors for a group of pesticides ranging in volatility and class (organochlorine, organonitrogen, organophosphorus, carbamate, and pyrethroid) that were fortified into a QuEChERS strawberry extract. The extract was then splitless injected into single taper liners with wool and without wool. The initial response factors were higher for the wool-packed inlet liner versus the liner without wool. After 60 analyses of strawberry extract on each liner, some of the more difficult pesticides showed lower response factors on both liner types, but overall the wool-packed liner still showed higher response factors than the liner with no wool.
A final part of the study compared response factors for deactivated quartz wool liner packing to deactivated borosilicate wool liner packing. Deactivated quartz wool was significantly better for analyzing dimethoate, chlorothalonil, carbaryl, methiocarb, dicofol, and deltamethrin.