Determination of REEs in natural water by ICP-MS with the aid of an automatic column changing system

An automatic column changing system was developed for preconcentration and measurement of rare earth elements (REEs) in natural water samples, where syringe driven chelating columns (SDCCs) were applied to the hybrid (off-line operation and on-line operation) solid phase extraction of REEs. The sample loading was carried out off-line prior to the measurement. After that, the SDCCs were set into the column holder of the automatic column changing system and REEs were on-line eluted and measured by an inductively coupled plasma mass spectrometer (ICP-MS). The present automatic column changing system permitted continuously automatic measurement of 30 samples, while 3 min was enough for measuring one sample. The reproducibilities of REEs' signals obtained with two kinds of SDCCs showed that both of them are fit for the hybrid solid phase extraction method for preconcentration of REEs. The analytical detection limits (ADL) of REEs were in the range from 0.013 pg mL(-1) for Tm to 0.15 pg mL(-1) for Ce when 10 mL of water sample was loaded to each SDCC. The usefulness of the present method was confirmed by analysing NMIJ CRM 7201-a. After that, REEs in Lake Baikal water samples from depth of 50, 100, 150, 200, 250 m were determined. The results showed that dissolved REEs in the sample of 50 m depth were significantly lower than other samples, while the total REEs in the sample of each depth were close to one another. The distribution of REEs in Lake Baikal water samples was also discussed using shale normalized REEs distribution pattern.