A novel semiautomated method for the estimation of free fatty acid in serum or plasma

A modification of the semiautomated assay method of Antonis (1965. J. Lipid Res. 6:307-312) for free fatty acid is presented. Free fatty acids are extracted from serum or plasma into di-n-butyl ether-2-methoxyethanol; the extract is almost free from phospholipids. The acids are analyzed in a portion of extract by a copper soap method using diphenylcarbazide. The extractant, being less dense than water, is easily separated from an aqueous phase both in the extraction of samples and in the assay of copper soaps. The assay is comparable in accuracy with well-tried titrimetric methods and is quicker and easier to operate.