Flow injection on-line group preconcentration and separation of (ultra)trace rare earth elements in environmental and geological samples by precipitation using a knotted reactor as a filterless collector for inductively coupled plasma mass spectrometric determination

A flow injection (FI) on-line filterless precipitation-dissolution system was developed for the ICP-MS determination of (ultra)trace REE in environmental and geological samples. A knotted reactor (KR), laboratory-made from PTFE tubing (200 cm×0.5 mm id), was used as a filterless collector. On-line precipitation of REE was achieved by mixing the sample with an ammonia buffer solution. The resulting precipitates were collected on the inner walls of the KR without filtration. A flow of 1 mol l –1 nitric acid was introduced to dissolve the collected precipitates and to transport the analyte to the ICP-MS system. Group REE preconcentration was achieved with separation from alkali and alkaline earth elements at pH 8.3-9.0. The method was demonstrated on-line with a Perkin-Elmer FIAS-400 FI system without modification. Using a preconcentration time of 120 s and a sample flow rate of 5 ml min –1 , a single preconcentration and separation with an enhancement factor of 55-75 were achieved within 5 min. The detection limits (3s) ranged from 0.06 to 0.27 ng l –1 . The precision for 16 replicate determinations of 0.1 µg l –1 of individual REE spiked in a porewater sample was in the range 1.8-4.2% (RSD). The accuracy of the method was demonstrated by analyzing a number of geological and environmental standard reference materials. The method was also applied to determination of ultratrace REE in porewater samples.