Analysis of Synthetic Pyrethroids by Gas Chromatography–Mass Spectrometry
2015
Gopal, Madhuban | Niwas, Ram | Devakumar, C.
The paper explains why we get many peaks during gas–liquid chromatography (GC) and attempts to rationalize the complicated GC spectra by identifying the major fragments of synthetic pyrethroids. In the present research, gas chromatography conditions in the electronic ionization (EI) mode were established that served as a benchmark in the development of a chemical ionization (CI) protocol for the selected ester and non-ester synthetic pyrethroids. CI technique is a lower energy process than EI. The lower energy yields less fragmentation, and usually a simpler spectrum with identifiable molecular ion. Common major peak in case of cypermethrin, deltamethrin, fenvalerate, and fenpropathrin was due to meta-phenoxybenzaldehyde moiety at m/z 208 (C₁₄H₁₀NO)⁺ ion. Etofenprox after protonation of ether oxygen loses one molecule of water producing m/z 359 instead of m/z 377 and it further fragmented to m/z 177 (C₁₂ H₁₇O)⁺ and 135 (C₉H₁₁O)⁺ ions. Above 70 % recoveries of all the pyrethroids at 0.1 and 1 μg ml⁻¹ levels were achieved from environmental samples. Improving analytical sensitivity and selectivity is important for quantifying trace pyrethroids in matrices. In EI mode, selecting base ion for single ion monitoring or using a precursor ion for MS/MS analysis, the lower limits of quantification (less than 0.1 ppm) become possible for the analysis of synthetic pyrethroids in water.
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