An improved assay with 4-(2-thiazolylazo)-resorcinol for non-esterified fatty acids in biological fluids.

S R Bergmann, E Carlson, E Dannen, B E Sobel

Index: Clin. Chim. Acta 104(1) , 53-63, (1980)

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Abstract

A simple and rapid colorimetric assay for non-esterified fatty acids (NEFA) was developed employing extraction of samples with 0.1 mol/l glycine (pH 2.7) and methoxyethanol : butyl ether, and formation of a copper-fatty acid soap detected with 4-(2-thiazolylazo)-resorcinol. The method developed is sensitive enough to detect as little as 11 nmol/0.25 ml sample. Results are not affected by marked molar excesses of phospholipids, cholesterol, cholesterol esters, triglycerides, bilirubin, or lactate. Recovery of palmitate in the extract averages 94.2 +/- 3.2% (S.D.) and other long chain fatty acids are recovered equally. The copper-NEFA-indicator complex formed is stable. Extracted samples can be stored for as long as 2 weeks without appreciable changes in measured NEFA content. The method developed is suitable for both manual and semi-automated procedures for determining NEFA content in biological fluids.