ECD-Dual-Column Pesticide Method Verification by Ion Trap GC/MS and GC/MS/MS

Soil extracts from five Superfund Contract Laboratory Program (CLP) laboratories were analyzed for organochlorine pesticides using gas chromatographic separation with ion trap mass spectrometric detection in both electron impact (GC/EIMS) and tandem mass spectrometry (GC/MS/MS) modes. These results were compared with those from the standard CLP dual-column gas chromatography electron capture detection (GC/ECD) pesticide method. This was accomplished to (a) determine the number of false positives and false negatives in the CLP data, (b) evaluate ion trap GC/MS/MS as a potential technique to replace/augment conventional ECD-dual-column methodology, and (c) to compare conventional ion trap GC/EIMS with the relatively new ion trap GC/MS/MS. In all, 16 pesticide extracts from five CLP laboratories were analyzed for 20 pesticides by GC/EIMS and GC/MS/MS, and the data were compared with the results from the CLP method (ECD-dual-column pesticide method). Of a possible 960 parameters (20 analytes × 16 samples × 3 data sets), there were 253 detections with concentrations ranging from 1 pg/μL to 77 ng/μL. The respective number of false positives and false negatives were 27 and 1 for GC/MS/MS, 6 and 10 for GC/EIMS, and 25 and 9 for the CLP data. Causes of erroneous results are discussed.