Classical and New Procedures of Whole Rock Dissolution for Trace Element Determination by ICP‐MS

Abstract

Sample digestion is a critical stage in the process of chemical analysis of geological materials by ICP-MS. We present a new HF ⁄ HNO 3 procedure to dissolve silicate rock samples using a high pressure asher system. The formation of insoluble AlF 3 was the major obstacle in achieving full recoveries. This was overcome by setting an appropriate digestion temperature and adding Mg to the samples before digestion. Sodium peroxide sintering was also investigated and the inclusion of a heating step to the alkaline sinter solution improved the recoveries of thirteen elements other than the lanthanides. The results of these procedures were compared with data sets generated by common acid decomposition techniques. Forty-one trace elements were determined using an ICP-QMS equipped with a collision cell. Under optimum conditions of gas flow and kinetic energy discrimination, polyatomic interferences were eliminated or attenuated. The measurement bias obtained for eight reference materials (BCR-2, BHVO-2, BIR-1, BRP-1, OU-6, GSP-2, GSR-1 and RGM-1) and intermediate precision (RSD) were generally better than ± 5%. The expanded measurement uncertainties estimated for two certified reference materials were mostly between 7 and 15%. New data sets for the reference materials are provided, including constituents with previously unavailable values and also for the USGS candidate reference material G-3.

Simple and cost-effective methods for precise analysis of trace element abundances in geological materials with ICP-MS

“…[21], (f) Ref. [7]. The numbers in the left of each subplot are the procedures: ① weighing; ② first acid attack; ③ evaporation; ④ redissolution; ⑤ oxide, hydroxide and instrumental drift corrections.…”

“…There are many digestion methods used in [3,7]. Likewise, microwave dissolution with open or closed oven procedures do not have adequate energetics to digest refractory phases, resulting in incomplete recoveries of some elements [7,8].…”

“…More recently, a mixture of NH4F-HNO3 [3] or HF alone [12] is also used. It is suggested that the addition of HClO4 is more effective to attack refractory minerals, such as those of the spinel group, and helps remove fluorides [7,17]. However, with issues such as safety and cost considered, very corrosive and explosive acids such as HClO4 or H2SO4 should be avoided in geochemical laboratories [3,16].…”

“…This is because (1) "pure reagent" of Mg 7 solution is required, which inevitably demands excess time and cost; and we also must know the (Mg + Ca)/Al ratio in each unknown sample solution; (2) it is very difficult to control the extent of sample dryness, since this procedure is sample dependent [3]; (3) it is also not recommended for small sample size because few reference materials have their homogeneity tested at the milligram scale and real samples are not expected to be more homogeneous than reference materials [7]. Hence, the aforementioned remedy is not recommended.…”

“…Detailed operating conditions and instrumental parameters are given in Table 1. The instrument was first optimized to obtain maximum signal intensities for 7 Ta count levels between samples in a wash solution of 1% Triton X-100 alternated with 2% HNO3.…”