Abstract
Since para-aminosalicylic acid has been found to have a definite chemotherapeutic effect in experimental tuberculosis, a simple method for its determination in blood appears desirable. The sulfonamide method in general use 1 cannot be employed without modification. In view of several requests for a method for determination of this substance, and since the slight modification of the sulfonamide method found necessary may prove useful with other aryl amines, we are publishing this short note.
No color is obtained when a solution of p-aminosalicylic acid is subjected to the ordinary procedure for determining sulfonamides. If the acidity of the solution is increased a color is obtained. Maximum color is developed at room temperature when the solution is made about 3 N with hydrochloric acid. The results are, however, not consistent. Diazotization for one minute gives a more intense color than for 3 or 10 minutes. Obviously, either the diazo compound is unstable or a secondary reaction is occurring with the nitrous acid. Diazotization done with the solution at 1°C and made 1 N with hydrochloric acid yielded a more intense color than any other procedure which we have tried. The results under these conditions appear to be quite consistent and reproducible.
Reagents. 1. A solution of trichloroacetic acid containing 15 g dissolved in water and diluted to 100 cc.
2. A 0.1% solution of sodium nitrite.
3. An aqueous solution of N-(1-naphthyl)-ethylenediamine dihydrochloride containing 100 mg per 100 cc. This solution should be kept in a dark colored bottle.
4. 6 N hydrochloric acid.
5. A solution of ammonium sulfamate, containing 0.5 g per 100 cc.
6. A standard solution of p-aminosalicylic acid prepared by suspending 50 mg of the compound in water and dissolving in slightly more than the theoretical amount of sodium hydroxide, and diluting to one liter.
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