Kinetic Spectrophotometric Determination of N-Acetyl-L-cysteine Based on a Coupled Redox-Complexation Reaction

Abstract

A novel simple kinetic spectrophotometric method for the determination of N-acetyl-L-cysteine (NAC) has been developed and validated. The proposed method is based on a coupled redox-complexation reaction, the first step of which is the reduction of Fe³⁺ by NAC; the second one includes the complexation of Fe²⁺, resulting from the preceding redox reaction, with 2,4,6-trypyridyl-s-triazine (TPTZ). The stable Fe(TPTZ)₂²⁺ complex exhibits an absorption maximum at λ = 593 nm.
The initial rate and fixed-time (at 5 min) methods were utilized for constructing calibration graphs. The graphs were linear in concentration ranges from 4.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ for the initial rate method and 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ for the fixed-time method, with detection limits of 1.0 × 10⁻⁶ and 1.7 × 10⁻⁷ mol L⁻¹, respectively. The proposed methods were successfully applied for the determination of NAC in its commercial pharmaceutical formulations.