The application of oscillating reactions to the analysis of real sampl
es by the analyte pulse perturbation technique is reported. The oscill
ating reaction involving the H2O2-NaSCN-CuSO4 system in an alkaline me
dium 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 paracetamo
l and 0.5-5 mu mol of ascorbic acid in real samples. The proposed meth
ods are precise (RSD < 5%) and have a reasonable sample throughput (6-
10 h(-1)) for this type of reaction, which can be implemented with mod
ular equipment available at any laboratory. The effect of influential
variables and the selectivity of the determinations was studied in rel
ation to the types of sample used. Determinations are virtually direct
and require no removal of interfering species. The results were valid
ated by comparison with standard methods.