Sample preparation is an essential step in the analytical process. It involves preparing a sample so that it can be analyzed accurately. The goal is to extract the analyte, the substance you want to measure, from the sample while removing any components that may interfere with the analysis. Sample preparation techniques vary depending on the physical state of the sample.
Bulk or large solid samples are typically reduced in size using grinding, crushing, or milling techniques to increase the sample surface area and provide a more efficient analysis. After grinding, the sample is sieved and mixed to ensure a uniform composition. The powdered sample is then dissolved in a suitable solvent to extract the analyte from the solid matrix. The solvent choice depends on the analyte's nature and the solubility characteristics of the sample components.
Liquid samples that contain suspended solid particles or precipitates are conventionally subjected to filtration or centrifugation to separate the solid impurities from the liquid. Filtration involves passing the liquid through a filter, while centrifugation uses centrifugal (spinning) force to separate the solids from the liquid phase. If the analyte is present in trace amounts, the liquid samples are subjected to pretreatment of concentration steps to increase the analyte concentration for better detection.
Sample preparation is usually unnecessary for analyzing gaseous analytes as the gas sample can be directly introduced into the analytical instrument.
Sample preparation is a critical step in obtaining accurate analysis results. It comprises three main objectives: extraction, purification, and concentration.
Firstly, extraction involves isolating a mixture with the analyte of interest from a sample matrix. Secondly, if interfering substances are present, they are removed to obtain a pure sample. Thirdly, if the extracted analyte is of low concentration, it is concentrated to a level that can be detected accurately.
The common forms of the sample are solid, liquid, and gas. Solid chunks too large to be directly analyzed are powdered by physical methods such as grinding, crushing, and milling.
Sieving and blending this mixture results in a homogeneous fine powder, which is then dried and dissolved in a suitable solvent to extract the analyte into the solution.
Unlike solids, liquid suspensions are filtered or centrifuged before analysis to remove impure solid particles.
As solid sorbents selectively adsorb the gaseous analyte, sample preparation is not required for gases.
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