Comparison of closed-pressurized and open-refluxed vessel digestion systems for trace elements in the residual fuel oil reference material (SRM 1634c)
Samples of residual fuel oil reference material (SRM 1634c) were mineralized in closed digestion vessels from Milestone Laboratory Systems (MLS) or from PAAR (HPA) or in open-refluxed microwave digestion flasks from Prolabo. The three digestion systems were evaluated in terms of accuracy and precision, reagents and time saving, total organic carbon content, and method determination limits for the determination of trace elements (Be, Mg, Al, Ca, V, Cr, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Te, Ba, Hg, Tl, Pb, Bi, U) by inductively coupled plasma-mass spectrometry. The total organic carbon concentrations were 1160 (MLS), 240 (HPA), and < 10 (Prolabo) mg C kg-1. Concentrations of V, Ni, and As in the digests of the HPA and the MLS systems were in acceptable agreement with each other and with the certified values for these elements. The values for Co when using the HPA and the MLS systems were lower than the certified Co value (~80%). Higher values for Se are probably due to interference by 82Kr. The digests of the HPA were prone to contamination by Fe and Al from the digestion chamber. The Prolabo system generally resulted in a substantial reduction in the concentration of elements, probably due to volatilization losses. It was also prone to sulfur-based interference. For the majority of the elements the relative standard deviations (RSD, n = 5) were less than 5% for HPA and MLS but were higher than 10% for Prolabo.