1-(4-Hydroxyphenyl)-, 1-(2,4-dihydroxyphenyl)- and 1-(2,5-dihydroxyphenyl)-2-bromoethanones: new labels for determination of carboxylic acids by high-performance liquid chromatography with electrochemical and ultraviolet detection.

A method is presented for the derivatization and determination of carboxylic acids by high-performance liquid chromatography with electrochemical and ultraviolet detection. The derivatizing reagents used in this study were synthesized, and their suitability was investigated for determination of drugs and metabolites with carboxylic acid groups. Quinoxaline-2-carboxylic, benzoic and salicylic acids each labeled with 1-(4-hydroxyphenyl)-, 1-(2,4-dihydroxyphenyl)- and 1-(2,5-dihydroxyphenyl)-2-bromoethanone were the principal esters studied; in addition, some antibiotics and their salts were also esterified. Conditions of derivatization are relatively mild at 60 degrees C for 60 min or less, and the reaction is 76% complete. The detection limits are as low as 1 pmol for some acids. Clean-up steps are not required to remove excess derivatizing reagent.