Specificity of the Free Fatty Acid Titration by the Method of Dole, Modified According to Trout

The specificity of free fatty acid (FFA) titration is significantly enhanced when the modification of Trout (5) is used and the heptane extract washed with dilute sulfuric acid. Lactate, pyruvate, acetate, -hydroxybutyrate, -ketoglutarate, citrate, and urate, in concentrations found in normal human plasma, will not interfere with the titration. It can be expected that in some exceptional pathologic conditions, lactate, pyruvate, acetate, -hydroxybutyrate, and urate will not be completely removed from the heptane extract. Salicylate seems to cause considerable interference. Trout’s procedure substantially reduces the interference caused by phospholipids. THE TITRATION of free fatty acids (F I’A) in human i)iaSflla, one may choose among the methods of Gordon (1, 2), Dole (3, 4), and Trout (5). The first method is highly specific but time-consuming. Time second method is relatively easy but not strictly specific for FFA: time interference of lactate, pyruvate, and acetate, when l)resellt in higimer than normal concentrations, can only be obviated by a double extraction. The modification of Trout (5), consisting of washing the heptane ex-tract-prepared according to Dole (3, 4)-with dilute sulfuric acid, combines the ease of Dole’s extraction method with time specificity of Gordon’s tecimnic. The following study was undertaken to evaluate to what extent the modification proposed by Trout enhances tile Si)eCifiCitv of Dole’s extraction procedure. Methods Aqueous solutions of lactate, pyruvate, acetate, $-hydroxyhutyrate, -ketogIutarate, citrate, imrate, and salicylate were extracted once, ac-cording to Dole’s procedure. One part of the heptane extract was titrated immediately, the other part after washing wit-h 0.05 % (v/v) sulfuric acid. Nile Blue A was used as indicator (6). Lipid phosphorus was estimated by the method of Bartlett (7). A heptane extract, free o