Solid-phase spectrophotometric determination of nickel in water and vegetable samples at sub-μg l−1 level with o-carboxylphenyldiazoaminoazobenzene loaded XAD-4

A highly sensitive and selective solid-phase spectrophotometric method for the determination of sub-μg l−1 level nickel(II) is described. Nickel(II) was sorbed on a styrene-divinylbenzene-type resin Amberlite XAD-4 as a Ni(II)–o-carboxylphenyldiazoaminoazobenzene (o-CDAA) complex. At pH 9.0, resin phase absorbances at 588 and 800 nm were measured directly with an apparent molar absorptivity of 2.95×107 g mol−1 cm−1. The linear range of the determination was 1.2–41 μg g−1 resin. The detection limit and the quantification limit were found to be 0.24 and 0.76 μg g−1 resin, respectively. The relative standard deviation of 10 replicate determinations of 1.0 μg nickel(II) in 100 ml sample was of 1.5%. The tolerance limit of coexistent ions was also investigated. Most of them are in tolerable amount. For practical analyses, 1 ml acetylacetone used can eliminate the interferences caused by Cu and Fe. The procedure was validated by analysis a certified water reference material (GBW 08618 Beijing, China) and a tomato leaf certified reference material (GBW 08402 Beijing, China) with the results in agreement with the certified values. The method was applied to the determination of nickel(II) in water and vegetable samples with satisfactory results.