HPLC analysis of brain and plasma for octanoic and decanoic acids

Two methods are described for determination of octanoic and decanoic acids in plasma and brain homogenate by "high-performance" liquid chromatography with ultraviolet detection. Analysis of the underivatized acids had a detection limit of only 50 mg/L, but formation of the p-bromophenacyl ester increased the sensitivity by 100-fold, to a detection limit of 0.5 mg/L. The latter procedure gave interassay coefficients of variation of 4.1% and 4.8% for octanoic and decanoic acids, respectively. The corresponding intra-assay values were 3.95% and 4.7% (n = 6). The derivative method, applied to samples of plasma from children receiving a medium-chain triglyceride (MCT) diet, gave values in agreement with results by gas-liquid chromatography. Results have also been obtained for samples from mice, either treated with the medium-chain triglyceride diet or given infusions of sodium octanoate.