Improving the specificity of the nitrosonaphthol procedure for urinary 5-hydroxyindoleacetic acid.

IN RECENT STUDIES (1) in which the urinary levels of 5-hydroxiiidoieacetic acid (5-HIAA) were measured by the nitrosonaphthol procedure (2), a chromophore was formed with the endogenous metabolite ill about 10% of the specimens from hospitalized patients which was not identical with that of the authentic reference compound. Although this method is widely used and is generally reiiable, the question of specificitv and consisteiicy has occasionally been raised (3-5). This probleni apparently has been resolved ill the present procedure by using an excess of sodium chloride during tile purification step with chloroform. Also, adjusting tile urine samples to tile same pH, rather than adding the same amount of acid to each, appears to have improved time Consistency and the specificity of the method. Furthermore, with the described extraction procedure, treatment of the urine with the dinitrophenylhydrazine reagent was not necessary.