Filterless preconcentration, flow injection analysis and detection by inductively-coupled plasma mass spectrometry

The influence of interferences in the analysis of elements by inductively-coupled-plasma mass-spectrometry (ICP-MS) may be significantly diminished by utilising a protocol of flow-injection analysis (FIA). The method is based on filterless preconcentration of metallic elements at the walls of a knotted reactor that was made of nylon tubings.

In the load mode, the preconcentration was accomplished by precipitation of metallic species in alkaline-buffered carriers onto the inner walls of the hydrofilic tube. After a preconcen-tration period of 40-120 seconds using sample volumes of 4-10 mL, the analyte was transferred by a FIAS 400 system to the ICP-MS detector by dissolving the species in an acidic carrier.

The magnitude of the enrichment factor largely depended on the time of preconcentration, on the pH-value of the preconcentration buffer and on the pH-value of the samples. Enrichment factors of 10-30 were obtained in the analysis of aluminium, of chromium and of iron, which resulted in detection limits (3) down to 20 g/L at a sampling frequency of 50 per hour.

The preconcentration protocol improves the selectivity thus allowing direct determination of the elements in saline media. Anionic species of common complexing agents, such as tartrate ions and thiocyanate ions, constituted the major inter-ferences to the method. Owing to the absence of columns in the manifold, an excellent repeatability was obtained, which allowed constant flow and long-time stability of the same knotted reactor without loss of preconcentration efficacy.