Spectrophotometric Determination of N-acetyl-L-Cysteine in Pharmaceutical Formulations by Flow Injection and Sequential Injection Analysis: Comparison of the Methods

N-acetyl-L-cysteine (NAC), a sulfhydryl-containing compound, is mainly used as a mucolytic and as an antidote for acetaminophen overdose. Flow injection and sequential injection systems were designed and optimized with the aim of providing precise, accurate and reliable flow methods for NAC determination in pharmaceuticals with very low sample and reagent consumption. Proposed methods are based on a redox reaction wherein NAC reduces a complex of Cu(II) and bathocuproine disulfonate (BCS) to orange [Cu(BCS)2]3– complex, which absorption was measured at λmax = 483 nm. The optimized FIA and SIA configuration yielded a linear calibration curve with correlation coefficients (R2 = 0.9999 and R2 = 0.9996) in the concentration range of 3.0 × 10–7 – 3.0 × 10–5 mol L–1 and analytical frequency of 120 h–1 for the FIA method and 4.0 × 10–7 – 4.0 × 10–5 mol L–1, at sampling rate 60 h–1 for the SIA method. The proposed flow methods were successfully applied for the determination of NAC in pharmaceutical products, as the results showed good agreement with the standard method prescribed by Pharmacopoeia. Recoveries were in the range from 98.4 % to 101.9 % for the FIA method and from 97.2 % to 101.8 % for the SIA method