文摘
A luminol chemiluminescence (CL) detection/flow injection analysis technique coupled with ion chromatography (IC) has been employed for the determination of low levels of Cu(II) and Co(II) in drinking water samples. The detection system was the CL of luminol/perborate or luminol/percarbonate in alkaline medium catalyzed by these transition metals. Oxalic acid in a solution of KOH and N(CH3)4OH was used as an eluent in the IC to improve the column selectivity (Dionex CS5A). Concentration and pH of the eluent affected simultaneously the CL intensity and the retention times (tR). Under the elution conditions used here, the retention times of both metal ions were much greater when the concentration of oxalic acid was decreased. Thus, Rt(Cu) = 2.15 min and tR(Co) = 4.50 min were measured at 80 mM oxalic acid concentration, while tR raised to 4.12 and 18 min for Cu(II) and Co(II), respectively, using a 10-mM concentration, but on the other hand, the CL signals showed substantially higher values when the concentration of oxalic acid was lesser in the eluent. An optimum oxalic acid concentration of 20 mM and an eluent pH = 4.7 were selected in order to have reproducible signals with a total analysis time of 10 min. The optimum flow rate for the mobile phase was 1.5 mL min−1. The concentration and pH of the postcolumn reagents also affected the CL signal, obtaining optimum concentrations of 5 mM for both oxidants (perborate or percarbonate) and luminol, this last dissolved in a 0.1-M borate buffer at pH 12. The optimum flow rate for the postcolumn reagents was 1 mL min−1. Linear calibrations for both transition metal ions were established, with calculated detection limits of 0.15 ng mL−1 for Co(II) and 0.20 μg mL−1 for Cu(II). Others ions commonly present in natural waters showed little or no interference. The method was successfully applied to water samples spiked with Cu(II) and Co(II), obtaining recoveries in the range of 85–128%, depending on the metal concentrations.
