Determination of methyl methanesulfonate and ethyl methanesulfonate in methanesulfonic acid by derivatization followed by high-performance liquid chromatography with ultraviolet detection.

Methanesulfonic acid is routinely used in pharmaceuticals but can contain potentially genotoxic impurities such as methyl methanesulfonate and ethyl methanesulfonate. The aim of this study was to develop a simple high-performance liquid chromatography with ultraviolet detection method for determining methyl methanesulfonate and ethyl methanesulfonate in methanesulfonic acid. Samples (250 mg) in water/acetonitrile (200 µL) were first combined with 10.0 mol/L sodium hydroxide solution (270 µL). Then they were mixed with 2.0 mg/mL N,N-diethyldithiocarbamate (500 µL), diluted to 5 mL with N,N-dimethylacetamide and allowed to react at 80°C for 1 h. The derivatives were analyzed using gradient high-performance liquid chromatography with ultraviolet detection (277 nm) and structurally elucidated by liquid chromatography with mass spectrometry. With acetonitrile/5 mmol/L ammonium acetate solution as the eluent and 1 mL/min as the flow rate on a C18 column, the derivatives were eluted at 10.6 and 14.8 min. Good linearity (correlation coefficients > 0.999) and low limits of quantitation (0.6 ppm) were obtained. The recoveries were in the range of 80-115% with relative standard deviation < 5.0%. Finally, the established method was successfully used for the determination of methyl methanesulfonate and ethyl methanesulfonate in methanesulfonic acid.