A Sensitive Photometric Procedure for Cobalt Determination in Water Employing a Compact Multicommuted Flow Analysis System

In this work, a multicommuted flow analysis procedure is proposed for the spectrophotometric determination of cobalt in fresh water, employing an instrument setup of downsized dimension and improved cost-effectiveness. The method is based on the catalytic effect of Co(II) on the Tiron oxidation by hydrogen peroxide in alkaline medium, forming a complex that absorbs radiation at 425nm. The photometric detection was accomplished using a homemade light-emitting-diode (LED)-based photometer designed to use a flow cell with an optical path-length of 100mm to improve sensitivity. After selecting adequate values for the flow system variables, adherence to the Beer-Lambert-Bouguer law was observed for standard solution concentrations in the range of 0.13-1.5 mu gL(-1) Co(II). Other useful features including a relative standard deviation of 2.0% (n=11) for a sample with 0.49 mu gL(-1) Co(II), a detection limit of 0.06 mu gL(-1) Co(II) (n=20), an analytical frequency of 42 sample determinations per hour, and waste generation of 1.5mL per determination were achieved.