Ion-exchange preconcentration and determination of vanadium in milk samples by electrothermal atomic absorption spectrometry

A new method for the electrothermal atomic absorption spectrometric determination of vanadium in milk and infant formulas using suspensions to avoid the need for previous dissolution of samples is described. Sensitivity is improved by a procedure based on preconcentration and removal of the matrix, using ion-exchange (Dowex 1X8-100). Suspensions of 15% (m/v) infant formula samples were prepared in a medium containing 0.05 M sodium citrate (pH 7.2) and passed through the ion exchange column. Vanadium was eluted from the column using 1 M hydrochloric acid and injected in the graphite furnace using a mixture of hydrofluoric acid plus magnesium nitrate as chemical modifiers. Calibration was carried out using multiple injection and aqueous standards prepared in the same medium. Detection limits were 0.2 ng g−1 for infant formulas and 0.02 μg L−1 for cow milk samples. The reliability of the procedure was checked by comparing the results obtained with those found using a previous mineralization stage and by analyzing five certified reference materials.