Spectrophotometric flow-injection determination of nickel in biological materials

A flow-injection procedure is proposed for the spectrophotometric determination of nickel in plants and foodstuffs using 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) as colour-forming reagent. Tolerance to the presence of potential interferants is enhanced by adding sodium pyrophosphate to the reaction medium and by coupling a C18 mini-column with immobilised 1-(2-thiazolylazo)-2-naphthol to the manifold. Linearity of the analytical curve is observed within 0.025 and 0.50 mg l−1 Ni (r=0.9997, n=8), and detection limit is 17 μg l−1 Ni. Precise results (r.s.d.≈1%) in agreement with certified values of standard reference materials are obtained at a sampling rate of 90 h−1 that means 0.47 μg Br-PADAP per determination.