Abstract
The reaction of Ehrlich's reagent, p-dimethylaminobenzaldehyde, with aromatic amines in acid solution has been made the basis of a colorimetric determination of sulfonamides by Werner 1 . and by Morris. 2 Fuller 3 has employed this substance in test papers for estimating the level of sulfonamide in laked blood after precipitation of proteins with an acid reagent, comparing the yellow color produced with standard color strips. The present paper describes the preparation of acid-containing test papers with which the level of sulfonamide can be estimated directly in serum without the addition of precipitating or acidifying reagents.
One gram of p-dimethylaminobenzaldehyde (straw-colored material is usable) is dissolved in 2 cc of concentrated hydrochloric acid and to the solution is added 0.8 cc of syrupy phosphoric acid (sp. gr. about 1.7) and water to make 100 cc. Large pieces of a good grade of absorbent paper (such as is used in making litmus paper) are soaked in the solution and immediately hung up to drain. When superficially dry, the papers are stored in the dark in covered glass jars for from 5 to 10 days, during which time most of the hydrochloric acid evaporates. The edges of the paper, which are usually yellow, are then trimmed off and the paper is cut into small strips and preserved in suitable vials. The strips are almost colorless, but become discolored if they come in contact with the skin at any time during preparation or use. The phosphoric acid remaining in the papers is sufficient to give a pH of approximately 3 when they are moistened with serum.
Estimation of the sulfonamide level is made by spreading evenly the serum to be tested over one end of an impregnated strip by means of a fine dropper, care being taken that unabsorbed fluid does not remain.
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