General High-Pressure Closed Acidic Decomposition Method of Rock Samples for Trace Element Determination Using Inductive
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General High-Pressure Closed Acidic Decomposition Method of Rock Samples for Trace Element Determination Using Inductively Coupled Plasma Mass Spectrometry Xijuan Tana, *, ** and Zhuming Wanga aLaboratory
of Mineralization and Dynamics, College of Earth Sciences and Land Resources, Chang’an University, Xi’an, 710054 China *e-mail: [email protected] **e-mail: [email protected] Received April 16, 2018; revised April 17, 2020; accepted April 17, 2020
Abstract—Complete decomposition is an essential prerequisite for accurate trace element quantification in geological samples. This work presents a general high-pressure closed digestion approach for rock samples from basic to acidic rocks by inductively coupled plasma mass spectrometry. Using HNO3−HF mixed system, different geological reference materials have been investigated for trace element determination, with acid ratio, decomposition time, digestion temperature, sample mass and reagent amount discussed in detail. In brief, 2.0 mL of HNO3−HF with the ratio of 1 : 1 and a digestion time of 12 h at 185°C in high-pressure sealed bomb are optimal for 50 mg rock sample decomposition. With relative errors under 10%, the analytical results of W-2a, BCR-2, GSP-2, AGV-2 and GSR-1 agree well with certified values. This proposed high-pressure sealed digestion method is characterized with less acid consumption, complete digestion and less damage for digestion process, well meeting the requirements for large sample throughput in geological laboratory. Keywords: high-pressure closed decomposition, acidic digestion, geological samples, ICP−MS DOI: 10.1134/S1061934820100147
Trace elements in geological samples provide important information on understanding the rock formation, mantle and crustal evolution and magmatism of planetary bodies [1–3]. Undoubtedly, the quality of analytical data is an essential index in the quantification of geochemical processes. To accurately determine trace elements in geological samples, complete sample decomposition is definitely a critical and fundamental stage [4–6]. There are many digestion technologies developed for the decomposition of geological materials, including alkali fusion [7, 8], open vessel acid digestions [9, 10], high-pressure closed acid digestions [11–13] and microwave dissolution [14, 15]. Due to the complex composition of geological samples, complete digestion of all sample types remains a problem in routine laboratory analysis. This is especially true for rocks containing resistant minerals such as zircon, garnet and spinel [16–18]. Owing to the relatively high backgrounds from the flux and high levels of total dissolved solids, it is known that alkali fusion method is subject to matrix-induced instability in inductively coupled plasma mass spectrometry (ICP−MS) analysis [19]. Despite being an amazing choice for decomposing rocks with acid-resistant accessory minerals, alkali fusion method is not recommended for trace element
quantification in geological samples. Open-vessel acid digestion and microwave digestion
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