Determination of trace amounts of tungsten with carminic acid by ion-exchange spectrofluorimetry

A spectrofluorimetric method for the determination of trace amounts of tungsten was developed, based on ion-exchange spectrofluorimetry. Tungsten reacts with carminic acid to give a red fluorescent complex, which was fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm quartz cell, was measured directly using a solid-surface attachment. The applicable concentration range was 1.0–20.0 µg l–1, with a relative standard deviation of 1.5% and a detection limit of 0.3 µg l–1. The method was applied to the determination of tungsten in natural waters. The method is more sensitive and selective than that using carminic acid alone.