Speed Up Multiresidue Pesticides Analysis in Food with an LPGC Rtx-5ms Column Kit for Low-Pressure GC-MS

• 3.1x faster with 54% less helium consumption compared to conventional methods.
• Get the speed advantage of LPGC-MS with a simple column change.
• Robust, factory-coupled column kit ensures leak-free performance.

Multiresidue pesticides analysis is a cornerstone of food safety testing, and labs are generally under pressure to manage both a high volume of samples and rapid turnaround time requirements. This creates demand for faster GC-MS and GC-MS/MS methods, but typical approaches involve expensive instrumentation or “fast GC” techniques that have capacity issues (narrow-bore columns) or MS-compatibility concerns (hydrogen carrier gas). Low-pressure GC-MS (LPGC-MS) is option that can provide significant speed gains without these drawbacks, but, historically, the challenging setup has been a barrier to implementation. As shown in this LPGC-MS pesticides analysis of 209 compounds in strawberry (Figue 1), all analytes elute quickly, with deltamethrin eluting last at 8.33 minutes. This time is three-fold faster than our analysis of the same extract on a conventional 30 m, 0.25 mm ID, 0.25 µm 5-type column where deltamethrin was again the final compound and eluted at 26.34 minutes. In addition to the speed improvement, the LPGC analysis used 54% less helium than the conventional method.

This LPGC-MS pesticides analysis utilizes a unique LPGC Rtx-5ms column kit (cat.# 11800) that is comprised of a narrow restrictor column (5 m x 0.18 mm ID) that is factory coupled to a wider Rtx-5ms analytical column (15 m, 0.53 mm ID, 1 µm plus 1 m integrated transfer line on the outlet end). Using this pre-connected kit allows the speed gains and helium savings of LPGC-MS to be obtained by making a simple column change and updating the instrument method with the new column dimensions, oven ramp, and flow rates. Note that for this particular LPGC-MS pesticides analysis, the GC oven must be capable of a 35 °C/min ramp rate at oven temperatures in excess of 300 °C. For 120V ovens, an oven insert kit will be necessary to achieve this rate.

While this LPGC-MS setup provides a significant speed gain; tall, narrow peaks that may improve sensitivity; and high capacity from the thick film analytical column, the overall plate count will be somewhat lower than on conventional columns. Although peak resolution will be lower with LPGC-MS, the mass spectrometer can offset this effect by spectrally distinguishing most target analytes. However, it is important to note that isobaric compounds must be chromatographically separated because the MS cannot resolve them. For example, in this analysis, isobars 4-4’-DDD and 2,4’-DDT are not fully resolved, so if their separation is critical, further method development would be needed. The other highlighted separations are compounds that either have both shared and unique ion transitions (trifluralin/benfluralin and cyhalothrin/acrinathrin); are adequately separated (cis- and trans-permethrin); or are commonly reported as a group (cyfluthrin and cypermethrin isomer clusters), and thus are still quantifiable even though they may not be completely chromatographically resolved.

For busy food labs needing faster methods, the speed gains of LPGC-MS pesticides analysis are an effective way to increase sample throughput. This once-challenging setup is now much simpler to implement using a low-pressure GC column kit from Restek.