Sample preparation is a critical step in the analysis of pharmaceutical products. The samples being prepared can come in many forms, as neat chemical compounds such as active pharmaceutical ingredients (API) or in complex matrices that support discovery and toxicological studies requiring the isolation of analytes from reaction byproducts, animal feed, biological fluids and tissues, waste streams, or environmental samples. All of these require sample preparation prior to analysis, which is the point in the method where the analyst will manipulate samples and have a direct effect on quantitative analysis. Since modern instrumentation is designed in many ways to self-check to ensure that it is working properly, sample preparation becomes a major source of laboratory deviations. Since sample preparation errors are often subtle and not easily diagnosed the proper application of these techniques is critical.
All sample preparation methods have their theoretical basis in chemical equilibrium, so an understanding of the fundamentals of chemical equilibrium is critical for developing, troubleshooting and investigating pharmaceutical methods is essential for the analyst. This chapter provides an overview of the fundamentals of extraction and chemical equilibrium, the traditional sample preparation techniques commonly employed in the pharmaceutical laboratory such as, direct injection, liquid liquid extraction and solid phase extraction along with some of the additional sample preparation methods that are establishing their place in lab, including solid phase microextraction, accelerated solvent extraction and microwave extraction, or are used to solve unique sample preparation challenges as in derivatization.
