Rapid determination of ions by combined solid-phase extraction–diffuse reflectance spectroscopy

We introduce colorimetric solid-phase extraction (C-SPE) for the rapid determination of selected ions. This new technique links the exhaustive concentration of an analyte by SPE onto a membrane disk surface for quantitative measurement with a hand-held diffuse reflectance spectrometer. The concentration/measurement procedure is complete in ∼1 min and can be performed almost anywhere. This method has been used to monitor iodine and iodide in spacecraft water in the 0.1–5.0 ppm range and silver(I) in the range of 5.0–1000 μg/l. Applications to the trace analysis of copper(II), nickel(II), iron(III) and chromium(VI) are described. Studies on the mechanism of extraction showed that impregnation of the disk with a surfactant as well as a complexing reagent results in uptake of additional water, which markedly improves the extraction efficiency.