How is a laboratory sample changed into a test sample?

In analytical chemistry, the laboratory sample is converted into a test sample through a series of operations designed to create a smaller, representative subsample suitable for analysis. The specific process depends on the nature of the material:12

• Particulate Solids: These are typically processed through comminution (grinding) to reduce particle size, followed by thorough mixing to ensure homogeneity. The volume is then reduced using techniques such as riffling or coning and quartering to maintain a representative sample.1
• Monolithic Solids: These may require surface preparation, such as grinding off oxides or acid dissolution, or mechanical processing like cutting, drilling, or milling to obtain a usable form.1
• Liquids and Gases: These require thorough blending or agitation to ensure uniformity. For gases, this may involve gentle warming of the storage vessel.1

Once the test sample is prepared, an analyst selects a test portion for measurement. If the analyte is present at low concentrations or interferences are present, further separation and purification steps—such as solvent extraction, ion exchange, or precipitation—may be required to isolate the analyte.23