Ramon M. Barnes

A mission of analytical chemistry is to develop and apply techniques and methods for the qualitative, semi-quantitative, and quantitative determination of chemical species (e.g., molecules, elements, oxidation states, etc.) in materials as a function of their temporal and/or spatial distributions. Chemical analysis is a complex multistage undertaking that may be summarized by a series of steps, sub-tasks, and operations. This approach is known as the “analytical sequence”. Various analytical sequences have been represented in the literature, and the important features of a generalized sequence will be described in this lecture. Steps involve problem definition; method selection; sampling; sample pretreatment; analyte measurement; data evaluation, and problem resolution. Although an analysis sometimes is outlined as a linear progression, the investigation often requires an iterative process rather than the linear series of steps. The approach usually involves an unsolved problem by analyzing one or more samples with a validated method. Before proceeding to a detailed description of samples, the steps that an analyst should consider for chemical analysis are reviewed. These tasks are arranged in a sequence, some of which are discussed in this lecture.
In the laboratory the sample typically is subjected to appropriate treatment before the analyte determinations. This treatment can be a simple physical operation or the complete transformation of a solid sample into a solution compatible with the determination method. The way to decompose the sample for analysis depends on its nature, the elements to be determined and their concentrations, and, in some cases, the ratio between the test sample mass and volume of solution, so that sample dilution does not impair the relative detection limit of the method. Sample treatment may involve a substantial transformation of sought chemical species into a suitable form for determination.