Improved solid-phase spectrophotometry for the microdetermination of chromium(VI) in natural water.

A simple and sensitive solid-phase spectrophotometry procedure was improved for the microdetermination of Cr(VI). A 0.06 cm3 portion of a cation exchanger, Muromac AG 50W-X2, was used to concentrate the target Cr(VI) in a 20 cm3 water sample, and resin beads were introduced in a flow cell of 1.5 mm diameter and having a 10 mm light path length for measurements using a UV-visible spectrophotometer. Three lenses were used for focusing the incident light beam and for recovering light scattered by the solid phase in the cell. The sensitivity achieved was higher by a factor of 277 compared with that of the solution method, and the detection limit was 0.014 microg dm(-3). The recovery on spiked real water samples by the standard addition method was 96-101%. Favorable working and performance characteristics made it possible to directly determine sub-microg dm(-3) amounts of Cr(VI) in natural water samples.