A procedure for enriching and cleaning up Rhodamine B and rhodamine WT in natural waters, using a Sep-pak C18 cartridge

Abstract An enrichment and clean-up procedure is described for Rhodamine B and Rhodamine WT in natural waters. Sep-pak C18 cartridges were used to adsorb the Rhodamine dyes from aqueous solutions. Complete desorption of Rhodamine B and Rhodamine WT on the Sep-pak was achieved. The concentration of the dyes could be increased more than a 100-fold. The concentration of Rhodamine B in the North Sea during a tracer experiment was measured using three different methods. The Sep-pak procedure gave lower concentrations of Rhodamine B than the direct fluorometric measurements. It is concluded that when the Sep-pak procedure is used to enrich Rhodamine dyes there is no interference from salts, pH, pigments and natural fluorescence on the dye fluorescence. This enrichment and clean-up procedure has advantages in tracer experiments. With the same amount of dye it is possible to measure for a longer period. For short experiments, less dye needs to be used.