Colorimetric determination of copper in aqueous samples using a flow injection system with a pre-concentration poly(ethylenimine) column

A colorimetric flow injection-system for the determination of Cu(II) in waters based on complexation reaction with 4-(2-pyridylazo)-resorcinol, usually termed PAR, is described. Performing measurements in 0.25 mol l−1 HNO3 medium allowed improved selectivity of the analytical method. The lack of sensitivity deriving from the low complex absorption under acidic conditions was balanced by the insertion of an immobilised poly(ethylenimine) (PEI) column where Cu(II) pre-concentration in neutral media occurs. Using sample volumes ranging from 2 to 4 ml, sampling rates of 24 and 12 samples h−1 within a detection limit of 25 and 13 μg l−1, respectively, were accomplished. Accuracy of the developed methodology was assessed by comparison with atomic absorption spectrometry being the relationship [FIA] mg l−1=1.00 (±0.03)×[AAS] mg l−1+0.00 (±0.02) obtained after analysing 15 samples. Precision was also evaluated using two samples of 0.05 and 0.5 mg l−1 copper, and a relative standard deviation (R.S.D.) better than 3% was attained for both.