On-line preconcentration system for nickel determination in food samples by flame atomic absorption spectrometry

Abstract

An on-line preconcentration system for nickel determination in natural foods has been developed. In it nickel(II) ions are fixed on a minicolumn packed with Amberlite XAD-2 loaded with 2-(2-benzothiazolylazo)-2-p-cresol (BTAC) through complexation process. Afterwards, nickel is eluted with 0.10 mol l−1 hydrochloric acid and determinated by flame atomic absorption spectrometry (FAAS). Chemical and flow variables, as well as common interferences effect, were studied. Nickel can be preconcentrated with an enrichment factor of 30, for a sample volume of 7.0 ml and a preconcentration time of 1 min. In these experimental conditions, the method provides a linear relationship between absorbance and nickel concentration in the range from 5.0 to 250.0 μg l−1, with a detection limit (3σ) of 1.1 μg l−1. The precision (assessed as the relative standard deviation (R.S.D.)) for seven independent determinations reached values of 5.0–0.9% in nickel solutions of 5.0–250.0 μg l−1 concentration, respectively. Achieved sampling rate was 48 samples/h. The enrichment factor and the detection limit can be further improved by increasing preconcentration time without degradation in the efficiency, due to the favorable kinetics and low hydrodynamic impedance of the present system. The nickel determination in four reference materials: spinach leaves (NIST 1570), orchard leaves (NIST 1571), peach leaves (NIST 1547) and rice flour (NIES 10), confirmed the accuracy of the proposed procedure. These results demonstrate also that the method is tolerant the presence of others metal ions in proportions agreeing with biological samples. Achieved recoveries of nickel in several natural food samples, measured by standard addition technique, proved also that this procedure is not affected by matrix interferences and can be applied satisfactorily for food analysis.