Simple and sensitive ion chromatography method for the simultaneousdetermination of Dimethyl sulfate and Diethyl sulfate contents in Metoprololtartrate drug substance

A simple and sensitive ion chromatography method has been developed for the simultaneous determination of dimethyl sulfate and diethyl sulfate contents in Metoprolol tartrate drug substance. Efficient chromatographic separation was achieved on AllsepTM anion column 150 mm long with 4.6 mm i.d., 7 μm particle diameter. Mobile phase consists of 4.0 mM aqueous phthalic acid. The mobile phase was delivered in an isocratic mode at a flow rate of 1.0 mL min-1 at ambient temperature conditions and the analytes were monitored by conductometric detector. The drug substance was subjected to stress conditions of hydrolysis, oxidation, photolytic, thermal and humidity degradation. The method was validated for specificity, precision, linearity, solution stability and accuracy. The limits of detection (LOD) and limits of quantification (LOQ) established for dimethyl sulfate are 1.06 μg mL-1 and 3.20 μg mL-1 respectively. For diethyl sulfate LOD is 1.47 μg mL-1 and LOQ is 4.46 μg mL-1. The average recoveries for dimethyl sulfate and diethyl sulfate are in the range of 99.5% to 102.4% and the method can be successfully applied for the routine analysis of Metoprolol tartrate drug substance.