ABSTRACT

The metabolic profiles of biological fluids from normal individuals contain a plethora of endogenous low mass metabolites, the composition of which depends upon the sample type (plasma urine, bile, etc.) and factors such as the species, strain, age, gender, diet, and gut microfloral composition of the organism fromwhich the sample derives and, indeed, even

the time of day at which the sample was taken. To this can be added the changes brought about in these endogenous profiles due to disease or toxicity, and the presence of the drugs and xenobiotics (and their metabolites) used to treat the condition, or in the case of toxicity, that caused it. To understand and interpret the changes in profiles observed during metabonomic studies, it is vitally important to identify and characterize these metabolites, both known and unknown, when they are observed. It is the authors’ intent to illustrate how both endogenous molecules and the metabolites of xenobiotics can be identified using modern spectroscopic techniques either alone or combined with either off-line methods or fully on-line hyphenated techniques. Whilst there is some overlap between the techniques used for exogenous and endogenous compounds, the strategies adopted for them do show some differences and these will be highlighted by the use of suitable illustrative examples. In general, we make the assumption that metabonomic analysis of biofluids will begin with 1H NMR of the unprocessed biofluid, complemented as required with HPLC-MS and work with extracts.