Application of inductively coupled plasma mass spectrometry for total metal determination in silicon-containing solid samples using the microwave-assisted nitric acid–hydrofluoric acid–hydrogen peroxide–boric acid digestion system

Abstract

The microwave-assisted conventional HNO₃–HF–H₂O₂–H₃BO₃ digestion system has been explored for direct ICP-MS analysis of total metals in silicon-containing solid samples. In closed Teflon PFA vessels under microwave heating with temperature/pressure regulation, a 0.25 g portion of sample containing ⩽ 33% silicon was digested in 1.5 ml of HF (48%), 5 ml of concentrated HNO₃ and 2 ml of H₂O₂(30%), followed by a second digestion stage with 12 ml of 5% m/v boric acid. The amount of HF used was approximately twice the stoichiometric requirement for 33% silicon contained in the samples, assuming all silicon exists as silica. The amount of boric acid used was the stoichiometric requirement for the HF added. With a sample dilution factor of 2000 (v/m), the end solution contained ⩽ 0.17% total dissolved solids for ICP-MS analysis. The ICP-MS system was calibrated by the method of external standards prepared in reagent blank solutions with in as the internal standard. The sensitivity of the In signal in a 5–8 h operation was only decreased by 5–10%. Background interferences from the digestion reagents were studied and corrected. The method developed is simple and rugged and suitable for routine analysis of at least 25 elements: Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th, Ti, Tl, U, V and Zn. The recoveries for most of these elements in standard reference materials including coal fly ash, urban particulate matter, sediment and soil were within 90–110%, and the relative standard deviations were within 5%. The method cannot determine B and is not suitable for Hg determination. The detection limits for Be and Se determination are not adequate.