Spectrophotometric determination of N-acetyl-L-cysteine using leucoxylenecyanol FF

A simple and sensitive method for spectrophotometric determination of N-acetyl-L-cysteine (NAC) with leucoxylenecyanol FF (LXCFF) has been elaborated. The method is based on the following reaction sequence: NAC is oxidised with potassium iodate to the colourless product and a stoichiometric amount of I - is formed. The latter is subsequently oxidised to I 2 with the excess of potassium iodate in acidic medium. Finally, iodine oxidises LXCFF to the blue-coloured xylenecyanol FF (XCFF). Absorbance of the formed dye was measured at pH 4.0 ± 0.1 at λ max = 613 nm. The measured absorbance obeyed Beer's law over the NAC concentration range 0.2-1.6 μg mL -1 ; apparent molar absorptivity was 9.58 × 10 4 L mol-' cm-'. Optimum reaction conditions providing maximum and constant absorbance have been estimated. The proposed method has been successfully applied to the determination of NAC in pharmaceutical preparations.