Methods for determining the amount of at least one metal analyte present in a liquid or gas sample of a halosilane supply (e.g., a chlorosilane supply) are disclosed herein. A sample of a halosilane supply is contacted and reacted with an aqueous hydrofluoric acid solution to produce a liquid reaction mixture. Liquid from the liquid reaction mixture is evaporated under controlled temperature and pressure conditions to near dryness. The nearly-dry residue is prepared for spectral analysis. The presence of a detectable amount of at least one metal analyte is determined for the sample.