Sample preparation gets material ready for analysis with equipment like a chromatograph, which can be used to determine the contents of a compound. Raw samples usually cannot be inserted directly into scientific equipment because they contain impurities or are in a form the equipment cannot readily interpret. They must be carefully handled and prepared to get them ready for testing, in controlled conditions to limit the chance of errors. A number of varying techniques are available for use with different kinds of samples.
Technicians start with a raw sample they may have collected or received for analysis. They determine which sample preparation technique to use after assessing the nature of the material and deciding what kind of testing they want to use. The sample may need to be concentrated because the material of interest is highly diluted, or treated to remove contaminants that might interfere with testing. Preparation of a sample can include filtering, dissolving, grinding, and other activities to convert the sample to a format that will be readable in equipment.
A technician might, for example, want to use sub-sampling in sample preparation. This allows for testing of a small component of the original sample to preserve it so it can be used in repeat or different tests. It’s important to get a representative sample to avoid inaccurate results, so the sample needs to be carefully handled to extract a good sub-sample for analysis.
Working conditions need to be carefully controlled in sample preparation. Anything introduced to the sample must be known so the technician avoids accidental contamination. For example, if a chemical needs to be subjected to a chemical reaction so it can be read in a scientific instrument, the technician must use the right reactive agent. All containers and equipment used should be clean, and the bench environment clear to avoid mixing up containers and methods.
Individual labs may have their own sample preparation protocol. A lab manual discusses the available techniques and provides recommendations for the handling of specific materials of interest. This documentation can increase consistency in testing, ensuring that no matter which technician performs a test, the sample would be handled in the same way. Customers of a lab may request documentation to assure themselves that tests are performed appropriately; for example, a lab that tests samples from athletes to check for doping should do so in a manner consistent with recommendations made by a governing body so its results will be valid.