How to Prepare a Sample for Chemical Analysis

The success or failure of a chemical analysis hinges largely on the proper sample preparation. Lab technicians spend up to 80 percent of their time preparing chemical analysis samples. Preparation of samples demands an intricate knowledge of exactly what type of analysis will produce the best, most accurate results, and excellent knowledge of what to look for in the final sample in order for the chemist to get an accurate analysis of the properties that make it up.

Instructions

    • 1

      Use clean equipment in all cases.

    • 2

      Choose liquid extraction without changing the properties of the organic material. Liquid extraction is popular with smaller labs and with chemists with limited resources. Liquid extraction, or liquid-liquid extraction, is the process of defining compounds based on their solubility in different liquids. The two liquids must be homogeneous or miscible. The most common liquids for the test are water and another organic solvent such as alcohol, acetone, or octanol.

    • 3

      Select centrifugation for liquids. The centrifuge is the type of chemical preparation machine most people are familiar with from television crime shows. The centrifuge uses gravity, known as g-force, to pull solids away from liquids and separate various components in a chemical analysis. During the spinning, the components with the most density move away from the central axis, and the lighter, less-dense chemicals move to the axis of the spin.

    • 4

      Use the solid phase extraction, SPE, for a more cost-effective chemical analysis preparation method because it is faster than the other types of extraction methods as well. Solid phase extraction is a popular method because it solves some of the difficulties presented by other methods of preparation, such as incomplete or uneven mixing. The drawbacks are that it is somewhat more complicated than the other two types of preparation and requires more precision as well. There are four phases of SPE, each with a specific use, depending on the type of sample being prepared. The phases are reversed phase, normal phase, ion exchange, and adsorption. Regardless of which phase you use, they all use a variation of silica and must absorb into the compound. As the compounds bind to the silica, they separate to generate the distinction between chemical compounds.

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