Simple Spectrophotometric Determination of Trace Amounts of Zinc in Environmental Water Samples Using Aqueous Biphasic Extraction

A simple and highly selective and sensitive extraction spectrophotometric method is presented for the determination of trace amounts of zinc in environmental water samples. The method is based on the separation and preconcentration of zinc as its thiocyanate complex by aqueous biphasic extraction and subsequent determination by spectrophotometry. As a chromogenic reagent for the spectrophotometric determination of zinc, 5-(5-Bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]-phenol (5-Br-PAPS) was used. Aqueous biphasic extraction can be performed by dissolving polyethylene glycol and sodium sulfate in a water sample. A rapid phase separation technique for this aqueous biphasic system was developed using thermal convection so that the extraction of zinc can be accomplished within 7 minutes without mechanical centrifugation. The calibration curve is linear in the concentration range of 0 similar to 200 mu g L(-1) and the determination limit calculated with ten-times the standard deviation of the reagent blank value is 1.6 mu g L(-1). Interferences from foreign metal ions were removed by separation with aqueous biphasic extraction and masking with suitable reagents for individual metal ions. The proposed method was applied to the determination of zinc in tap water and river water samples. The obtained results were in good agreement with those obtained by inductively coupled plasma atomic emission spectrometry.