A Validated Stability Indicating GC-NPD Method for Determination of Related Substances in Malathion Lotion

Abstract

A versatile stability indicating analytical method was developed and validated for determination of closely related impurities of malathion viz., malathion impurity J, malathion mono isopropyl ester and malathion di isopropyl ester using gas chromatography with nitrogen phosphorous detector (GC-NPD) in malathion lotion. The chromatographic separation was performed using a column with G1 stationary phase (dimethylpolysiloxane). As part of the method validation, specificity, limit of detection (LOD), limit of quantification (LOQ), linearity, accuracy, precision, robustness and ruggedness were determined. The limit of quantification values for malathion Impurity J, malathion mono isopropyl ester and malathion di isopropyl ester were 0.016, 0.012 and 0.009 %, respectively. Good linearity (r² > 0.99) was obtained ranging from limit of quantification to 150 %. Recovery was verified for all the three impurities at concentrations ranging from limit of quantification to 150 %. Percent recovery for malathion impurity J, malathion mono isopropyl ester and malathion di isopropyl ester were 104.2 to 113.5 %, 99.4 to 106.4 % and 97.4 to 114.1 % respectively. The admissible robustness indicates that the method remain unaffected by small but deliberate variations. Malathion was found to degrade in acid and base stress conditions. This method has been successfully applied to pharmaceutical lotion formulation and no interference for the excipients was found.