Application of Doehlert matrix and factorial designs in the optimization of experimental variables associated with the on-line preconcentration and determination of zinc by flow injection inductively coupled plasma atomic emission spectrometry

A simple and rapid method is described for the preconcentration and determination of zinc in waters. The method employs on-line preconcentration of zinc on a 3 cm x 3 mm column packed with silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide (DPTH-gel) and placed in the injection valve of a simple flow manifold. Five variables (sample flow rate, eluent flow rate, eluent concentration, pH and buffer concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Doehlert matrix designs. The optimum conditions established were applied to the determination of zinc by flow injection inductively coupled plasma atomic emission spectrometry. The proposed method has a linear calibration range from 2 to at least 500 ng ml(-1) of zinc, with a detection limit of 1.7 ng ml(-1) (S/N = 3) and a throughput of 40 samples h(-1) using a 60 a preconcentration time. Validation was carried out against certified reference water samples, and by determining the analyte content in sea water and synthetic sea water. The results showed good agreement with the certified values and sufficiently high recoveries.