Simultaneous analysis of organophosphorus and organochlorine pesticides in animal fat by gas chromatography with pulsed flame photometric and micro-electron capture detectors

A method using simultaneous pulsed flame photometric (PFPD) and micro-electron capture detection (μECD) in gas chromatography (GC) was developed and validated for the analysis of 23 organophosphorus (OP) and 17 organochlorine (OC) pesticides in animal fat. The method entailed the extraction of animal tissue (mixed with twice the sample weight of sodium sulfate) with 7 mL ethyl acetate per 1 g tissue. After the blending step, the extract was centrifuged and 3 mL cyclopentane was added to a 7 mL portion of the extract. A 2.5 mL portion was injected into a 2 cm ID×22.5 cm Biobeads S-X3 gel permeation chromatography column (4.5 mL/min flow rate of 70/30 ethyl acetate/cyclopentane). A 36 mL fraction (from 8 to 16 min) was collected, evaporated, and solvent-exchanged to 1 mL final volume in iso-octane. The GC/PFPD + μECD system used a single injector and column, but the flow was split after the chromatographic separation to the two detectors. The final extract was injected (2 μL) into the GC/PFPD + μECD system for simultaneous analysis of the OP and OC analytes. The PFPD was used in the phosphorus-only mode to detect OPs and the μECD mainly detected halogenated pesticides but a few N-containing OPs could be sensitively detected with it as well. Recoveries were 60–70% for the bulk majority of pesticides except for methamidophos, acephate, and omethoate which are more difficult in GC analysis due to their more polar nature. Fenthion and phorate also gave more variable recoveries, presumably due to their degradation to sulfones and sulfoxides. In fortification recovery experiments at several different concentrations over multiple days, reproducibilities of 10–20% relative standard deviation were achieved, and limits of quantitation were typically 10–20 ng/g.