Cloud point extraction and simultaneous spectrophotometric determination of V(V), Co(II) and Cu(II) ions in water samples by 5-Br-PADAP using partial least squares regression

In this work, a new method has been proposed to simultaneously determine V(V), Co(II) and Cu(II) ions from aqueous solution by spectrophotometry after cloud point extraction using partial least squares regression (PLS). The metal ions in 10 ml of aqueous solution (containing 0.2 M sodium acetate buffer solution, pH 3.5) were formed complexes with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). Then, Triton X-114 (2 %, v/v) was added to the solution. By increasing the temperature of the solution up to 55 °C, a phase separation occurred. After centrifugation at 3,000 rpm for 10 min, the surfactant-rich phase was dissolved and diluted to 0.5 mL with ethanol. The metal ions were then determined using spectrophotometry. At these optimal extraction and operating conditions, linearity was obeyed in the range 7–300, 3–100 and 15–700 ng mL−1 of V(V), Co(II) and Cu(II), with the detection limit of 2.2, 1.0 and 4.5 ng mL−1, respectively. The relative predictive error for the simultaneous determination of 15 test samples of different concentrations of V(V), Co(II) and Cu(II) was 3.28, 3.64 and 4.04 %, respectively. The root mean square error of prediction for applying the PLS method to 15 synthetic samples in the linear ranges of these metal ions was 3.4, 1.6 and 18.1 ng mL−1. The interference effect of some anions and cations was also tested. The proposed method has been applied successfully to the simultaneous determination of V(V), Co(II) and Cu(II) ions in real matrix samples with the recoveries of 96.75–104.80 %.