Abstract
A rapid method has been established for the potentiometric determination of N-acetyl-L-cysteine, glutathione, and D-penicillamine by argentimetric titration using an iodide-selective electrode. The reaction involved was (1), and the iodide ion produced by the reaction with iodine in methanol was determined.
R-SH+3I2+ 3H2O = R-SO3H+6HI…(1)
In a typical example, a sample containing (0.0088.6) mg N-acetyl-L-cysteine or (0.01515) mg glutathione or (0.0086.2) mg D-penicillamine was taken into a 100 ml amber-glass titration cell, 8 ml of 5 M sulfuric acid (except D-penicillamine) was added and operated with excess of an 0.05 M iodine-methanol solution. After the solution was made up to 50 ml with redistilled water, it was then titrated potentiometrically with a (0.00010.1) M standard silver nitrate solution at room temperature. All operations of the titration procedure were performed at 10 min. N-Acetyl-L-cysteine {(0.088.6)mg}, glutathione {(0.615)mg}, and D-penicillamine {(0.36.2)mg} were determined with a relative error and relative standard deviation of less than 1 %. The best results with a relative error and relative standard deviation of less than 0.3 % were obtained using 8.6 mg of N-acetyl-L-cysteine, 15 mg of glutathione, and 6 mg of D-penicillamine. The commercial samples of N-acetyl-L-cysteine, glutathione, and D-penicillamine were determined by this method.
