Quantitative Estimation of Barbiturates in Blood by Ultra-Violet Spectrophotometry: I. Analytical Method

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Abstract
The pronounced absorption of u.-v. light at 234 millimicrons by the 5,5-dialkyl substituted barbiturates in aqueous soln. at pH 10, in contrast to the transparencies of these soln. at pH 2 is used as a basis for the detn. of barbiturates in blood. A tungstate filtrate of the blood to be analyzed is prepared. The barbiturate is removed from an aliquot of the filtrate by successive chloroform extractions. The chloroform is dried with NaSO4 and extracted once with dilute alkali. The pH of the alkali solution is adjusted to the range 9-10.5 by addition of H2SO4, and the absorption spectrum of the resulting soln. is detd. It is then acidified, and its absorption redetd. The decrease in absorption at 239 millimicrons on acidification is proportional to the barbiturate present in the original blood. As little as 0.4 mg. barbiturate/100 ml. of blood may be detd. in a specimen of 5 ml. of blood. Salicylate and sulfadiazine interfere, but may be recognized by their characteristic absorption spectra.