Formation and suppression of AlF₃ during HF digestion of rock samples in Teflon bomb for precise trace element analyses by ICP-MS and ID-TIMS

Abstract

Abstract:An aluminum fluoride, A1F;3, forms during HF digestion of felsic rock samples, for trace element and isotope geochemistry, which use a Teflon bomb at high temperature and pressure. The AIF;3 incorporates trace elements (Rb, Sr, Y, Cs, Ba, REE, Pb, Th, and U), and can not be decomposed by conventional methods such as evaporation with HC104. The production of this A1F;3 results in lower yields and poor accuracy in analyses of these trace elements by ICP-MS. The formation of AlF;3 is controlled by the chemical composition of the rock samples, in particular, A1F,3 does not form during decomposition of mafic samples with relatively high (Mg+Ca)/Al ratios. We have developed a new method to suppress the AlF;3 formation, in which excess Mg is added to the sample prior to acid digestion in the bomb. This new method makes it possible to accurately determine the trace element compositions of higher-Al rock samples with lower concentrations of Mg and Ca (e.g. rhyolite and granite). In the trace element analyses by TIMS with isotope dilution techniques (ID-TIMS), AlF.3 formation hinders the achievement of isotope equilibrium, resulting in erroneous results. However, the Mg-addition method removed this problem by suppression of AlF;~ formation.

Slab decarbonation and CO2 recycling in the Southwestern Colombian volcanic arc

“…The Teflon Ò bomb decomposition method (4 days at 245°C) was used for samples containing acid-resistant minerals such as zircon (Makishima et al, 1999). To the silica-rich samples such as dacites and rhyolites, magnesium was added in order to suppress AlF 3 formation during the acid digestion processes at 245°C using Teflon Ò bomb (Takei et al, 2001). All major and trace elements analyses were run in duplicated sample.…”

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

“…Varying combination of strong acids is commonly used in the acid digestion of silicate materials, such as HF-HClO4 [8,13,14], HF-HNO3 [1,11,13,15], HF-HCl-HClO4 [14], HF with aqua regia (1 HNO3: 3 HCl) [16], HF-H2SO4 [4,8,13] or HF-HBr-HNO3. More recently, a mixture of NH4F-HNO3 [3] or HF alone [12] is also used.…”

An Improved Procedure for the Determination of Ferrous Iron Mass Fraction in Silicate Rocks Using a Schlenk Line‐Based Digestion Apparatus to Exclude Oxygen

“…The use of HF with H 2 SO 4 for the decomposition of silicates is a common practice and can thoroughly liberate Fe 2+ . We attempted to reverse the order of addition, but it resulted in the precipitation of insoluble fluorides, always associated with Mg, Ca, or Al that contained ferrous iron mass fraction, that also contained some ferrous iron and therefore yielded low results (e.g., Yokoyama et al 1999, Takei et al 2001. An interesting phenomenon was observed as shown in Figure 5c, where JP-1 and GBW07112 achieved lower values without HF while the values for JG-2 and GSR-2 were identical with or without hydrofluoric acid treatment.…”