Sample preparation technique used prior to instrumental analysis of metals.

• A. Sieving
• B. Acid digestion
• C. Liquid-liquid extraction
• D. Clean-up

Answer: (B)

Dissolving the sample so metals are present as soluble species in a liquid is essential for most instrumental analyses of metals. Acid digestion uses strong acids to break down the sample’s matrix and convert metals into soluble ionic forms, giving a uniform solution that can be accurately measured by techniques like atomic absorption, ICP-OES, or ICP-MS. This step removes the solid matrix and minimizes matrix effects, enabling reliable calibration and quantification.

Sieving only separates particle sizes and doesn’t dissolve the material, so it won’t prepare the metal content for these analyses. Liquid-liquid extraction is useful for separation or preconcentration, but it’s not a universal dissolution step and adds extra stages. Clean-up targets removing interferences after dissolution, not the primary dissolution itself.