Method development data – Stabilization of volatile silicon species in hydrofluoric acid (HF) digests of biological samples for HF-free silicon analysis by ICP-MS

Experiments were conducted in the U.S. Geological Survey (USGS) Aqueous Trace Element Analysis Laboratory (ATEAL) in Denver, CO to support development and validation of a method for preparing biological materials for silicon analysis by solution phase inductively coupled plasma mass spectrometry (ICP-MS). The objective was to stabilize volatile silicon species resulting from a digestion method utilizing hydrofluoric acid (HF) during evaporative removal of HF from the sample. Removal of HF prior to ICP-MS analysis is necessary to avoid its deleterious effects on sample introduction components made up of quartz resulting in high background signals and preventing measurement of trace concentrations of silicon. Experiments were designed to test efficacy of salts of Group I elements, including lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium nitrate (RbNO3) and cesium chloride (CsCl) for stabilization of volatile silicon species. The effects of alcohols, namely methanol and n-propanol, solution acidity and heating/drying schemes were investigated to achieve effective stabilization of silicon species. Silicon background signals from the evaporated and unevaporated test solutions were measured using a HF-susceptible quartz sample introduction setup (PAF-Quartz) and a fully HF-inert PAF-Sapphire setup to determine the analytical merits of the method. Method validation was performed by determining silicon concentrations in several plant and tissue standard reference materials.