Use of tertiary amines to neutralize hydrofluoric acid for the ICP-OES analysis of silicon (M5)

Full text: The ICP analysis of hydrofluoric acid digests is complicated by the need to remove free fluoride aqueous ions by either volatilization or complexation prior to aspiration through a quartz transport system. Volatilization of free fluoride requires a laborious and dangerous technique involving the use of perchloric acid with evaporation to near dryness which results in the loss of silicon. Complexation of free fluoride requires the use of boric acid which not only tends to clog quartz concentric nebulizers but also does not completely neutralize fluoride which results in variable blanks for silicon. W.R. Grace's analytical method for the analysis of major and minor elements in zeolites, catalysts and clays calls for the volatilization of free fluoride which required that the concentration of silicon be calculated by difference. To increase accuracy, Grace sought a method to easily analyze for silicon. The method chosen is one in which the silicate samples were dissolved in Teflon pressure digestion vessels using a combination of nitric - hydrochloric - hydrofluoric acids. The digestates were neutralized using the spectrasol tertiary amine reagent which deactivates all free fluoride. The resulting samples were aspirated into an ICP using a quartz concentric nebulizer for analysis of silicon. Data correlating the ICP results with more conventional methods will be presented and discussed. (author)