Understanding the Reasons for Erroneous Determinations of Boron in Silicon following Wet Chemical Digestion in HF/HNO3

Abstract

The correct and precise analytical determination of boron in silicon is a well-known challenge, which often manifests in highly scattered single determinations or significant sub-determinations. In the present work, all individual steps, such as the digestion of the silicon under variation of the reaction conditions, the removal of the silicon and acid matrix by volatilization as well as dilution of the evaporated residue in diluted acids, i.e. the preparation of the final analyte solution, were investigated. If experimental failures in digestion and volatilization can be ruled out, the main reason for deviating, scattered or minor results is the existence of a boron-silicon complex, which withstands the entire sample preparation procedure and is finally present in the analyte solution. Depending on the chosen agent used to dilute the residue after evaporation, a soluble form or an insoluble form is obtained. The insoluble form can be removed from the sample solution by filtration, sedimentation or partial retention within the sample introduction system of the ICP-OES or ICP-MS and thus causes occasionally falsified results of the boron analysis.

Keywords: boron determination, silicon, ICP-OES, boron silicon species, 11B ss-MAS NMR