Determination of 25 Trace Element Concentrations in Biological Reference Materials by ICP-MS following Different Microwave-Assisted Acid Digestion Methods Based on Scaling Masses of Digested Samples
The use of normalized procedures designed for soil and sediment samples (like US-EPA 3051) to chemically prepare some kind of organic samples is a common practice in some laboratories. However, the performance of this method for other matrices has to be demonstrated. Three microwave-assisted digestion procedures with 0.5？g of sample and simplified reagents (10？mL HNO3 alone and mixtures of HNO3/HCl- and HNO3/H2O2 procedures A, B, and C, resp.) were compared for quantitative determination of 25 elements (Be, B, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, Pb, Th and U) in three biological reference materials provided by NIST (mussel tissue (MT), tomato leaves (TL), and milk powder (MP)) by ICP-MS. From scaling masses (from 0.1 up to 0.9？g at 0.1？g interval) in procedure A, a linear relationship among instrumental signal and mass of digested sample could be constructed at 99% CL for most of the target analytes. The slope of this linear fit provided the estimation of sample concentration, while the ordinate in origin allowed the identification of matrix interferences which were absent in the reagent blank. 1. Introduction Inductively coupled plasma mass spectrometry (ICP-MS) is a robust and widely used technique for multielemental and isotopic analysis of environmental materials [1–3] that has shown clear advantages when compared with other analytical techniques such as inductively coupled plasma atomic emission spectrometry (ICP-AES) [4–6], flame atomic absorption spectrometry (F-AAS), and electrothermal atomic absorption spectrometry (ET-AAS) [7, 8]. The basic setup for ICP-MS analysis requires the sample introduction as a liquid solution and thus, for solid matrices, an acid digestion procedure becomes mandatory. Sample digestion is mainly carried out by a fusion or a wet procedure based on an acid digestion with a heated mixture of mineral acids [2, 9–13]. In general, closed digestion systems are to be preferred to minimize possible contamination of the digest, increase reproducibility, and avoid losses of volatile elements [14–17]. Wet microwave digestion equipped with temperature and pressure control assisted by common mineral acids, such as nitric, sulphuric, perchloric and hydrochloric acids, is frequently used for sample digestion [18]. In order to dissolve the silicates and eliminate the effects of silica gel in environmental samples, hydrofluoric and orthoboric acids are usually used, although they can produce unsatisfactory recoveries in volatile elements [19, 20]. A mixture of nitric acid and hydrogen peroxide
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