The complexity and wide range of organic acids present in urine, and other biological fluids, makes their quantification and positive identification a difficult problem. Although chromatographic characteristics of individual compounds, such as retention data on gas, liquid and thin-layer chromatography, are extremely useful indicators of probable identity, it is necessary to use a technique with sufficient specificity to make a positive identification of a chromatographically separated component. Infra-red spectroscopy, for example, may be suitable when enough material in a pure form is available. In the case of a total urinary organic acid extract, such an approach is only practical on a very limited scale owing to the large number and wide variation in concentration of the components.