Simultaneous gas chromatographic determination of chlorpyrifos and its impurity sulfotep in liquid pesticide formulations

Abstract

An analytical method for simultaneous determination of the active substance (chlorpyrifos) and its relevant impurity (sulfotep) in commercial pesticide formulations has been developed and validated. The proposed method entails extraction of the analytes from samples by sonication with acetone and analysis by gas chromatography-flame ionization detection (GC-FID). The proposed method was characterized by satisfactory accuracy and precision. The repeatability expressed as relative standard deviation (RSD) was lower than the acceptable values calculated from the modified Horwitz equation whereas individual recoveries were in the range of 98-102% and 80-120% for chlorpyrifos and sulfotep, respectively. The limit of quantification (LOQ) for the impurity (sulfotep) was 0.003 mg mL(-1) corresponding to the maximum permitted level according to Food and Agricultural Organization of the United Nations (FAO) specifications for the active substance (chlorpyrifos) being 3 g kg(-1) of the chlorpyrifos content found. The main advantage of the proposed method was a considerable reduction in the analysis time since both analytes were determined based on a single injection into the GC-FID. Analysis of real samples of commercial pesticide formulations confirmed fitness-for-purpose of the proposed method.

Identification and Characterization of the Isomeric Impurity of the Fungicide “Cyazofamid”

“…The four aromatic chemically equivalent protons of cyazofamid exhibited a multiplet at 7.29-7.34 but in the case of the impurity, these four protons appeared as two separate signals: a doublet for 2 protons at 7.27 and another doublet for 2 protons at 7.81. The 1 H and 13 C data indicated that the N, N-dimethyl sulphoxide group could be in ortho position to a chlorine atom in the case of the isomeric impurity 2.…”

“…Cyazofamid showed the following signals: S5). 1 H-NMR shows the two chemically equivalent methyl group NÀ (CH 3 ) 2 of cyazofamid as a singlet at 2.66 ppm and also observed two peaks at 131.3 and 38.1 ppm in 13 C-NMR (2C). However, the peaks were shifted in the spectra of impurity ( 1 H: singlet at 3.16 ppm; 13 C (2C): 127.2 and 38.91 ppm).…”

“…The 1 H and 13 C NMR study were performed under a 400/500/ 600 MHz NMR spectrometer (Bruker) using CDCl 3 as the solvent. The chemical shifts ( 1 H and 13 C) are reported on the δ scale in ppm, relative to tetramethylsilane (TMS) δ 0.00 in 1 H NMR and CDCl 3 at 77.0 ppm in 13 C NMR.…”

“…In the past, most of the researchers focused on the impurity profiling of the pharmaceutical products but not the agrochemicals. In recent times, researchers have been focusing on the impurity profiling of agrochemicals [7–13] . In these lines, we have developed high‐performance liquid chromatography (HPLC), gas chromatography/mass spectrometry, and nuclear magnetic resonance (NMR)‐based analytical methods for investigating the impurity profile of bifenthrin [2] …”

“…In recent times, researchers have been focusing on the impurity profiling of agrochemicals. [7][8][9][10][11][12][13] In these lines, we have developed high-performance liquid chromatography (HPLC), gas chromatography/mass spectrometry, and nuclear magnetic resonance (NMR)-based analytical methods for investigating the impurity profile of bifenthrin. [2] Cyazofamid, chemically known as 4-chloro-2-cyano-N,Ndimethyl-5-p-tolylimidazole-1-sulfonamide (Scheme 1), is a fungicide belonging to the phenylimidazole family that has broad spectrum activity against plasmodiophoromycetes and oomy-cetes with various sites of action.…”