Dansylation of aromatic, aliphatic, and medicinal carboxylic acid compounds in 1 M Na2CO3 buffer

Dansyl chloride (DNS-Cl) is a sulfonyl chloride compound which is utilized as a fluorescent probe for quantitative analysis or structural studies of complex molecules. The fluorescent emission was sufficiently strong to permit detection of less than 10 μg of the carboxyl compounds studied here. The dansylation of aromatic carboxyl compounds (i.e. aspirin), aromatic primary amines, and aliphatic carboxyl compounds was accomplished in 1 M Na₂CO₃ buffer at pH 11. The fluorescent labeled analytes were then isolated by thin layer chromatography (TLC) or the aqueous mixture was pre-extracted with proline (or glycine) to eliminate back-ground emission originating from the hydrolized or sulfonic acid form of DNS-Cl. Fluorescent labeled analytes are clearly discerned under ultraviolet light. Limits of detection for dansylated carboxyl compounds was 1-5 μg, however for amines it was approximately 1 μg. Dansylation of aromatic primary amines proceeded much faster (15 min) than that of carboxyl compounds (≥1.5 h) at 25 °C. Despite the aqueous solubility of analytes, which ranged from less than 0.004-5.30 mg/ml, the dansylation of carboxyl compounds was effective. Various organic solvents for extracting derivatives from aqueous mixture were evaluated.