Multicomponent kinetic determination of Cu, Zn, Co, Ni and Fe at trace levels by first and second order multivariate calibration

A flow injection system coupled to a photodiode array spectrophotometer (FI-PDA) for the multicomponent kinetic determination of Cu, Zn, Co, Ni and Fe at trace levels is presented. The substitution reaction of metal-nitrilotriacetic complexes (M-NTA) by 4-(2-pyridilazo) resorcinol (PAR) instead of the direct complexation of the free ions with PAR is employed. In this way, the spectral differences between the colored complexes are combined with the different reaction rates of the ions producing a more specific lambda-time region for each metal enhancing the selectivity. Since the NTA-M-PAR system is fast and the pure analyte profiles appear partially overlapped in the time and lambda-axis, temporal and spectral information were added to PLS and PCR models to improve results and to increase the number of metals to be determined. The developed method provides the fast and cheap determination of the five metals at the sub-ppm range and demonstrates that the use of temporal and spectral information increases the number of analytes to be simultaneously determined, improving the analytical figures of merit as well.