Precise and Accurate Doping of Nanoporous Silica Gel for the Synthesis of Trace Element Microanalytical Reference Materials

Abstract

This paper presents an experimental procedure for fabricating high-purity silica glass that contains a selected element at a specified concentration. This technique is used to prepare glasses doped with trace-level concentrations of Ti with the goal of improving analytical confidence when measuring trace elements in quartz. Systematic tests were performed to determine the ideal conditions and procedures for doping nanoporous silica gel with the highest efficiency of dopant recovery. Silica gel was cleaned in concentrated HCl, immersed in a non-polar doping medium at a controlled pH and doped with precise quantities of ICP-MS standard solution. Using liquids composed of longer chain molecules as the doping medium diminishes recovery, suggesting that large molecules could obstruct nanopores to inhibit capillary uptake of the dopant. A control experiment using crystalline quartz reinforced the effectiveness of nanoporous silica gel for doping with trace-level precision. Layered aggregates of silica gel doped with different Ti concentrations were hot-pressed to create multi-layered reference materials that were analysed with multiple techniques at a variety of spatial scales. Analyses at the intra-grain scale (SEM-CL, EPMA), at the single grain scale (SIMS), at the sample layer scale (EPMA, LA-ICP-MS), and at the bulk scale (ICP-OES) demonstrate acceptable homogeneity at the analyte volumes characteristic of most microanalysis techniques and show that nanoporous silica gel holds promise as a highly retentive doping substrate for preparing trace element reference materials for laser-, electron-and ion-beam microanalysis.

A Griggs apparatus upgrade for stress-controlled testing of geological material at high temperature and pressure

“…We followed the Nachlas [37] cleaning and preparation procedures for silica gel to eliminate surface impurities, followed by heat treatment to reduce the water content at 825 °C for 1 h in a conventional furnace. We packed 0.16 g of dried silica gel with added 1 mL of deionized water (~0.6 wt%) between a set of 45°precut and polished yttria-stabilized zirconia (ZrO 2 ) pistons.…”

“…We followed the Nachlas [37] cleaning and preparation procedures for silica gel to eliminate surface impurities, followed by heat treatment to reduce the water content at 825 °C for 1 h in a conventional furnace. We packed 0 .…”

‘Box‐Profile’ Ion Implants as Geochemical Reference Materials for Electron Probe Microanalysis and Secondary Ion Mass Spectrometry

“…Also, a set of four silica glasses with known contents of Ti were prepared at the University of Edinburgh (Gallagher and Bromiley ). Recently, multi‐layered nanoporous silica gel was used to produce Ti‐doped high‐purity silica glass (Nachlas ). Although all these materials may be useful under some analytical conditions, their suitability as reference material is limited for microanalytical methods.…”

Natural and Synthetic Glass and Crystal Reference Materials for Trace Element Microanalysis

“…A complementary approach for preparing microanalytical reference materials is to fabricate silica glasses doped with precise quantities of the analyte of interest. An experimental procedure has been developed that utilizes the high retentivity of nanoporous silica gel as a doping substrate [2]. Silica gel contains a network of nanopores that exert a capillary force on polar dopant molecules, as well as surface silanol groups that have a strong affinity for the dopant species.…”