DETERMINATION OF NICKEL IN FOOD BY SPECTROPHOTOMETRY WITH o-CARBOXYLBENZENEDIAZO-AMINOAZOBENZENE

Abstract

ABSTRACT A highly sensitive and relatively interference-free spectrophotometric method for the determination of nickel is described. The method is based on color reaction between o-Carboxylbenzenediazoaminoazobenzene (o-CDAA) and nickel(II). The absorbance (at λmax = 540 nm) is linear up to 0.24 µg ml−1 of nickel(II) in borax buffer solution (pH = 10) with a repeatability(RSD) of 1.0% at a concentration of 0.2 µg ml−1. The molar absorptivity of Ni-o-CDAA-TritonX-100 is 3.3 × 105 l mol−1 cm−1, its limit of quantification and the limit of detection were found to be 0.74 and 0.22 ng ml−1 respectively, it gives a better sensitivity than other reagents published. The influence of reaction variables and the effect of interfering ions are reported; most of metal ions in food can be tolerated in considerable amounts. Only zinc may interfere with determination of trace nickel, but it can be eliminated by using a prior separation with sulfhydryl dextran gel adsorbent easily. Moreover, the synthesis of derivatives of benzenediazoaminoazobenzene and sulfhydryl dextran gel and the conditions of color reaction were studied in detail. The proposed method is very sensitive, simple and rapid, it has been used for the determination of nickel in food samples with satisfactory results.