* 2,2,4-trimethvl pentane..587 Determination of Fatty Acids in Small Amounts of Plasma and in Lipid Components of Tissues by Ultraviolet Spectroscopy

M ETLIODS for determining fatty acid com-position of fats and fatty materials, based on ultraviolet absorption spectroscopy of the alkali-isomerized fatty acids and iodine values, have been employed extensively for the past decade. The application of these methods for fatty acid analysis of small amounts of plasma or other tissues, however, has received less attention. In this discussion an attempt is made to show how these methods can be successfully applied to determine polyun-saturated fatty acids in one milliliter or less of plasmua, and in smuall fractions obtained in separation of tissue lipid components. (A) DETERMINATION OF POLYUNSATURATED ACIDS IN PLASMA So/vents: The type and purity of solvents for extraction of lipids from plasma or other tissues are extremely important. In our studies, it was found necessary to carefully redistill each solvent through a 30-inch Vigreux colummi to insure that it was free of nonvolatile residues and low in spectral density. The following absorbances of a number of solvents were found satisfactory. For 0.5 to 2 ml of plasma: If only small amounts of plasma are available, the fatty aci