Determination of rare earth elements in environmental matrices by sector-field inductively coupled plasma mass spectrometry

Abstract

In the framework of an international certification campaign, sector-field inductively coupled plasma mass spectrometry (sector-field ICP–MS) was used for the accurate determination of the rare earth elements in five candidate reference materials: aquatic plant, calcareous soil, mussel tissue, river sediment, and tuna muscle. All samples were taken into solution by use of microwave-assisted or mixed microwave-assisted / open beaker acid digestion. Subsequently, the samples were appropriately diluted and subjected to ICP–MS analysis.

Except for Sc, all the elements involved were determined at low mass resolution (R = 300). For Sc, application of a higher resolution setting (R = 3000) was required to separate the analyte signal from those of several molecular ions which gave rise to spectral overlap at low mass resolution. Some of the heavier REE can also suffer from spectral overlap attributed to the occurrence of oxide ions (MO⁺) of the lighter REE and Ba. This spectral overlap could be successfully overcome by mathematical correction. Matrix effects were overcome by use of two carefully selected internal standards, such that external calibration could be used. On each occasion, a geological reference material was analyzed as a quality-control sample and the reliability of all results obtained was additionally checked by means of chondrite normalization.

For tuna muscle the content of all REE was below the limit of detection. For calcareous soil and river sediment, low to sub μg g^–1 values were observed, whereas the REE content of aquatic plant and mussel tissue was considerably lower (low to sub ng g^–1).

Overall, the results obtained were in excellent agreement with the average values, calculated on the basis of all “accepted” values, obtained in different laboratories using different techniques.