Application of oscillating reaction-based determinations to the analysis of real samples

The application of oscillating reactions to the analysis of real samples by the analyte pulse perturbation technique is reported. The oscillating reaction involving the H2O2-NaSCN-CuSO4 system in an alkaline medium was used for the expeditious, convenient, automatic determination of vanillin, paracetamol and ascorbic acid in food and pharmaceutical samples. Six methods (two per analyte) were developed that allow the determination of 1.5-40 mu mol of vanillin, 0.5-6 mu mol of paracetamol and 0.5-5 mu mol of ascorbic acid in real samples. The proposed methods are precise (RSD < 5%) and have a reasonable sample throughput (6-10 h(-1)) for this type of reaction, which can be implemented with modular equipment available at any laboratory. The effect of influential variables and the selectivity of the determinations was studied in relation to the types of sample used. Determinations are virtually direct and require no removal of interfering species. The results were validated by comparison with standard methods.