Improved Methods in the Gasometric Deter- Mination of Free and Conjugated Amino- Acid Nitrogen in the Urine

Our original method for the determination of the total aminoacid nitrogen’ (free plus conjugated), although it gave accurate results and has been used successfully by ourselves and others, required a somewhat cumbersome manipulation before the urines were ready for the final amino determination. After being acidified and heated in the autoclave to hydrolyze the urea, the ammonia was boiled off on a hot pIate with lime, a process requiring careful watching for an hour or more, and rather offensive because of the odors evolved. The calcium sulphate and hydrate were then filtered, the filtration and washing requiring anot’her hour. The washings, of about 500 cc. volume, were then concentrated on the water bath, which required two or more hours additional. These manipulations have been greatly simplified by the ascertainment of the fact that one has merely to filter off the alkaline solution obtained after adding the lime, and concentrate the filtrate on the water bath to dryness, in order to drive off every trace of ammonia. This process dispenses entireIy with the troublesome boiling off of the ammonia. The washing of the precipitate of calcium salt)s can also be avoided to advantage by making the mixture up to a definite volume before filtering, and taking an aliquot portion of the filtrate for the rest of the determination. All the operations are furthermore rendered more convenient by the use of the micro-apparatus for determining the