Reply to “Comments on the ‘classical equations’ given in J. Chromatogr. A 1024 (2004) 195–207”, by L.S. Ettre

Development and refinement of sample preparation protocols for retrospective detection and identification of chemical warfare agents (CWAs) and their markers is of paramount importance from verification point of view of chemical weapons convention (CWC). Precursors of nitrogen- and sulfur-mustards (NMPs and SMPs) are polar adsorptive markers of vesicant class of CWAs. Their detection in a given environmental sample may imply past contamination with mustards. For the efficient extraction of NMPs and SMPs from soil, on-matrix derivatisation–extraction (OMDEX) method was developed and optimized. The method involved trifluoroacetylation of analytes on soil itself, followed by extraction with suitable solvent. The extracted samples were analyzed by gas chromatography–mass spectrometry (GC–MS). This virtually single-step sample preparation offered better recoveries of NMPs and SMPs in comparison to conventionally used extraction, evaporation and derivatisation. The best recoveries of analytes were obtained with acetonitrile by OMDEX method. Dynamic linearity range of trifluoroacetylated (TFA) derivatives of NMPs and SMPs was 1–12 μg/L in GC–MS analysis in SIM mode. Repeatability and reproducibility of this technique containing 5 and 10 μg analytes/gm soil was <3.3% and <4.6%, respectively. OMDEX technique was finally applied for the detection of TFA derivatives of NMPs in the soil sample supplied in 16th official proficiency test conducted by OPCW in October 2004.