Automated modification of Duncombe's method for the ultramicro determination of serum free fatty acids.

An automated continuous-flow method is described for estimating free fatty acids in serum using 25-mul samples. The procedure depends on the formation of copper soaps on the surface of a semipermeable membrane, their transfer into chloroform, and subsequent determination of dissolved copper. The membrane separating copper reagent and chloroform is supported between thin-channel dialysis plates. Chloroform extracts of serum free fatty acids are passed through the dialysis unit, and dissolved copper in the outflow is estimated colorimetrically. The procedure gives values that agree with a standard titrimetric method.