Residue studies of fosetyl aluminium in citrus fruit on LC-MS/MS

A two year residue study of Fosetyl Aluminium on citrus was carried out following five applications of Fosetyl Aluminium 80% WP @ 3.2 g a.i./L water and 6.4 g a.i./L water at an interval of one month. An easy and simple methodology was standardized for the extraction of residues in citrus fruit and soil followed by estimation and confirmation on LC-MS/MS using C₁₈ column by keeping the electrospray ionisation source (ESI) in negative ionisation mode. The methodology was validated for selectivity, linearity, precision, repeatability, reproducibility and its limit of detection and quantification. The limit of quantification (LOQ) was worked out to be 0.05 mg kg⁻¹. The results of recovery studies were consistent and more than 80 per cent in all the matrices. Precision in terms of repeatability (RSD_r) and reproducibility (RSD_R) was calculated to be below 20 per cent. No residues above LOQ were detected in any of the samples collected at different time intervals.