An integrated reaction-retention and spectrophotometric detection flow system for the determination of nickel

An integrated flow-through photometric sensor for the determination of nick el in real samples of various origins has been developed. The sensor is bas ed on the reaction of NI(II) with 1-(2-pyridylazo)-2-naphthol (PAN) immobil ized on a cationic resin which was placed in a flow-cell using a spectropho tometer tuned at 566 nm as detector. The Ni(II) ion from the sample injecte d into the carrier stream (pH = 5.0) of a monochannel continuous flow syste m reacts with the immobilized chromogenic reagent to form a red chelate whi ch remains on the active solid support and generates the analytical signal. When this reached its maximum value the Ni(II)-PAN chelate was destroyed u sing 1 M H2SO4 as eluents, leaving the sorbed PAN untouched. The response o f the sensor was linear in the three concentration ranges assayed: 0.3-4.0, 0.1-1.6 and 0.05-0.8 mu g mL(-1) for sample volumes of 100, 400 and 800 mu L, respectively, and the R.S.D.(%) (n = 10) were 1.80(100 mu L), 3.04(400 mu L) and 2.29(800 mu L). The sensor showed an excellent selectivity which could also be increased with a simple on-line modification to avoid interfe rence from copper. It was applied to a variety of real samples with very go od results in all cases.