A rapid LC/MS/MS method for simultaneous determination of levodopa, carbidopa, entacapone and their six related compounds in film-coated tablets.

RATIONALE: An LC-MS/MS method has been developed and validated to determine levodopa, carbidopa, entacapone, and corresponding six related substance - levodopa impurity B, levodopa impurity C, methyldopa, methylcarbidopa, entacapone impurity C, and entacapone impurity A - in film-coated tablets at the first time. METHODS: Chromatographic separation was achieved with a gradient elution by using a C18 column, a mobile phase containing 0.5% formic acid in water and 0.5% formic acid in methanol. The mobile phase flow rate was 0.5 mL min(-1) . The UV detector was set at 280 nm and the triple quadrupole mass spectrometer was used in MRM mode. RESULTS: The LOD and LOQ results were 1.3 and 3.94 ng mL(-1) for levodopa impurity B; 5.26 and 15.9 ng mL(-1) for levodopa impurity C; 0.833 and 2.53 ng mL(-1) for methyldopa; 3.31 and 10.0 ng mL(-1) for methylcarbidopa; 1.67 and 5.06 ng mL(-1) for entacapone impurity C; and 0.61 and 1.86 ng mL(-1) for entacapone impurity A. CONCLUSIONS: The method was rapid, linear, accurate, and reproducible. The LC/MS/MS method that was developed to determine the related substances and assay of levodopa, carbidopa, and entacapone can be used to evaluate the quality of regular samples in the pharmaceutical industry. It can be also used to test the stability of samples.