On-line elution of iron hydroxide coprecipitate carrier for determination of REEs in natural water by mix-gas ICP-MS

A new coprecipitation method using iron hydroxide was developed to preconcentrate rare earth elements (REEs) in natural water prior to determination by inductively coupled plasma mass spectrometry (ICP-MS). The precipitate was collected in a syringe filter, which was connected into an ultrasound-assisted on-line elution and ICP-MS measurement system for REEs. Nitrogen (120 mL min−1) was mixed in auxiliary gas of ICP-MS to get rid of the oxide spectral interference with the REEs' measurements. When 10 mL of water sample was used, the blanks of REEs were from 0.001 pg mL−1 of Tm and Lu to 0.22 pg mL−1 of La and Ce. Detection limits calculated from 3-fold standard deviation of blanks were from 0.0006 pg mL−1 of Tm to 0.21 pg mL−1 of Ce. Recoveries of all REEs were from 97.1% to 103.1% with good reproducibility (standard deviation less than 3.3%). The usefulness of the method was confirmed by comparing the analytical results of NMIJ CRM 7201-a obtained with the present method and those obtained with an established solid-phase extraction method.