This study reports on the dissipation of acephate residues on brinjal and okra and the formation of the metabolite methamidophos. The QuEChERS method in conjunction with gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) was used for analyzing acephate and methamidophos in brinjal and okra. The limit of detection (LOD) and limit of quantification (LOQ) were 0.003 and 0.01 mg kg⁻¹ for both compounds, respectively. The recoveries were between 76.6-99.5% with the relative standard deviation (RSD) between 3.2-11.8% (n = 6). The measurement uncertainty (MU) was between 9.9-17.5% at 95% confidence level. The initial residues of acephate were 8.61 and 13.63 mg kg⁻¹ on brinjal, and 8.44 and 15.05 mg kg⁻¹ on okra from treatments at the standard and double doses of 560 and 1,120 g a.i. ha⁻¹, respectively. The concentration of methamidophos increased up to the third day on brinjal and okra and decreased thereafter. Methamidophos was more persistent than acephate. The pre-harvest intervals (PHI) required for dissipation of the combined residues of acephate and methamidophos to below the European Union maximum residue limits were 47 days for brinjal and 25 days for okra. The results of the study can be utilized for use of acephate in plant protection of brinjal and okra.
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