Measurement of Caffeine and Its Metabolites in Biological Fluids

Methods for the detection and quantification of caffeine in biological material have paralleled the development of analytical technology in general. Early in this century, the analysis of caffeine depended on its purification and a classical approach to chemical identification (Salant and Rieger 1912). Subsequently, ultraviolet spectrophotometry was introduced in the 1940s (Ishler et al. 1948; Fisher et al. 1949), paper chromatography in the 1950s (Cornish and Christman 1957), gas chromatography in the 1960s (Grab and Reinstein 1968), and liquid chromatography and radioimmunoassay in the 1970s (Cook et al. 1976). These advancements not only tended to add sensitivity, ease, and specificity, but also increased the feasibility of measuring metabolites as well as caffeine itself. Tobias (1982) has recently reviewed several methods for the assay of caffeine in critical detail. We present an overview of the various procedures, selected methodological details, and a brief discussion of the advantages and disadvantages of the various options. Because caffeine is not measured routinely in clinical laboratories, there is no recommended or selected method of clinical chemistry.