RESEARCH STUDY ON THE STABILITY OF AQUEOUS N-ACETYLCYSTEINE SOLUTIONS

A research study has been conducted on N-Acetylcysteine quality problems caused by HPLC-methods. 2-Methylthiazolin-4-carboxylic-acid is formed as an artificial byproduct during HPLC sample preparation in aqueous acidic solution. Kinetic research studies show that 2.5 % of the Thiazolin-carboxylic-acid occur after about 30 min. A maximum value of about 9 % is analysed after 6-7h. As a consequence various analytical HPLC results of aqueous N-Acetylcysteine solutions have been found. A more precise HPLC purity analysis can be achieved through immediate sample injection and external calibration with the byproducts N,N'-Diacetylcystine and N,S-Diacetylcysteine. MTC is formed in even smaller amounts at pH values >4. Under these conditions the redoxpotential of the ACC mercapto-group and a rapid oxidation of ACC to N,N'-Diacetylcystine can be observed.