Solid-phase extraction (SPE) of the fluorescence tracers uranine and sulphorhodamine B

This paper describes a technique to analyse and to enrich the fluorescent dyes uranine (Acid Yellow 73) and sulphorhodamine B (Acid Red 52) from leakage water. A solid-phase extraction (SPE) using C18 material was developed for the pretreatment and the extraction of the dyes. ENV + ®, a highly crosslinked polystyrene divinylbenzene polymer, was a suitable sorbent for uranine but not for sulphorhodarnine B. Additionally, the samples were purified from interferences and natural background substances. The optimum pH value was 3 for the extraction, because the molecules were then uncharged and retained by the sorbent. A methanol/aqueous buffer solution (pH 10) was required for eluting the dyes from the sorbent, since the molecules were then negatively charged and soluble in methanol/water. After extraction the samples were pure enough to be analysed by HPLC with the fluorescence detector. Using HPLC analysis the tracers could be measured simultaneously under constant conditions. The tracer enrichment was 500-fold by SPE, so much lower amounts of tracers can be applied in the natural environment. Therefore, the cost of tracer experiments could be reduced. The dyes could be applied in combined tracer experiments, since both tracers could be determined by the same analytical procedure.