Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed us ing low-pressure gas chromatography-mass spectrometry (LP-GC-MS). No specia l techniques for injection or detection with a common quadrupole GC-MS inst rument were required to use this approach. The LP-GC-MS approach used an an alytical column of 10 mx0.53 turn I.D., 1 mum film thickness coupled with a 3 mx0.15 mm. I.D. restriction capillary at the inlet end. Thus, the condit ions at the injector were similar to conventional GC methods, but sub-atmos pheric pressure conditions occurred throughout the analytical column (MS pr ovided the vacuum source). Optimal LP-GC-MS conditions were determined whic h achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC-MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injecti on volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labi le analytes, such as carbamates; and (v) due to larger sample loadability l ower detection limits for compounds not limited by matrix interferences. Th e optimized LP-GC-MS conditions were evaluated in ruggedness testing experi ments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared wi th the conventional GC-MS approach. The matrix interferences for the quanti tation ions were worse for a few pesticides (acephate, methiocarb, dimethoa te, and thiabendazole) in LP-GC-MS, but similar or better results were achi eved for the 16 other analytes, and sample throughput was more than doubled with the approach. (C) 2001 Published by Elsevier Science B.V.