Investigation of the efficiency of the sample pretreatment stage for the determination of the Rare Earth Elements in rock samples by inductively coupled plasma mass spectrometry technique

Different methods of rock sample digestion for final analysis by ICP-MS technique are investigated. It is shown that only basic rocks can be quantitatively digested in a microwave (MW) field with the mixture of HF and HNO3 acids at 210 °C for 60 min. The addition of HCl and H3BO3 provides complete digestion of andesites and some types of granites. Even at maximal temperature in the used MW oven of 210 °C syenites, granodiorites and albitized granites are not digested. These types of rocks are not digested in a closed Teflon autoclave for 16 h and can be digested only by fusion with lithium metaborate. The reason for such behavior is discussed. To avoid problems with the introduction of heavily acidic solutions after fusion in ICP the solutions were diluted. To compensate the loss of sensitivity due to the dilution step the REEs (Rare Earth Elements) pre-concentration using aminocarboxylic Pol-DETATA (diethyltriaminetetraacetate) sorbent was tested. The developed scheme is validated by the analysis of a wide range of reference rock materials.

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► We used ICP-MS with microwave digestion for determination of REE in different rocks.
► Syenites, granodiorites and albitized granites are not digested in the MW at 210 °C.
► We explain this fact by the presence of stable saturated silicate–albite NaAlSi3O8.
► These rocks can be digested completely only by fusion with lithium metaborate.