In situ analysis of trace elements in quartz by using laser ablation inductively coupled plasma mass spectrometry

Abstract

There are several benefits which would result from the development of an in situ analytical technique for ultra trace elemental analysis of quartz, including rapid screening of possible high-purity quartz resources, by eliminating the need to remove solid and liquid inclusions by expensive dressing techniques prior to chemical analysis of structural impurities. Information on the petrogenetic history of the quartz can also be obtained from the distribution of trace elements. The main purpose of this paper is to describe an analytical method for estimating the concentrations of structural bounded trace elements in quartz. A double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS, Finnigan MAT model ELEMENT), with the CD-1 Guard Electrode and a 266-nm UV laser ablation system was used in the development of the method for in situ analysis of quartz. The following elements are included in the analytical protocol: Al, Ba, Be, Cr, Fe, Ge, K, Li, Mg, Mn, Pb, Rb, Sr, Th, Ti, U. Analyses were carried out in low mass resolution ( m/Δ m=300), except for Mg, Ti, Cr, Fe (medium mass resolution, MR, m/Δ m≈3500) and K (high mass resolution, HR, m/Δ m>8000). The isotope 29Si was used as an internal standard at low resolution, and 30Si at medium and high resolution. External calibration was done by using the international reference materials: NIST 612, NIST 614, NIST 616, NIST 1830 from the National Institute of Standards and Technology (NIST), BCS 313/1 from the Bureau of Analysed Samples (BAS), the rhyolite RGM-1 reference sample from the United States Geological Survey (USGS), Reston and the certified reference material “pure Substance No. 1” silicon dioxide SiO 2 from the Federal Institute for Material Research and Testing, Berlin, Germany (BAM). Because of the absence of an SiO 2 blank, the BAM no. 1 SiO 2 was used for the estimation of detection limits. Detection limits for most of the elements are between 0.2 and 0.01 μg g −1. Analysis time and laser spot size were adjusted so that the raster did not exceed 300×300 μm on a 200-μm-thick section. New data for the international reference materials BCS 313/1 (BAS) and NIST 1830 and the standards BR-K1 and BR-FR2 are reported. To improve the lower limit of quantification and analytical uncertainty at low concentrations, it is important to have calibration curves with well defined intercepts. This can be achieved by the use of certified standards, with trace element concentrations lower than the BAM no.1 SiO 2 or a sample blank.