Determination of carboxylic acids by liquid chromatography after phase-transfer-catalysed fluorogenic labelling

Labeling of free carboxyl groups

The latest trends in the labeling of free carboxyl groups for high-performance liquid chromatography are reviewed. The labeling reagents for fluorescence detection are mainly discussed according to their reaction type (or functional group). Attention is also paid to the reagents used for ultraviolet detection and for enantiomeric separation. The reactivity and sensitivity of the reagents used for the labeling of carboxylic acids are described.

Liquid chromatographic monitoring of pseudocholinesterase activity: comparison of methods

In order to study the activity of pseudocholinesterase in vitro, two liquid chromatographic techniques have been developed. One is based on phase transfer-catalyzed (PTC) esterification of the carboxylic acid formed during hydrolysis of the substrate, and the other on the use of a radioisotopically labeled substrate. In both cases, the substrate used was a long-chain choline ester. The PTC method, utilizing (N-9-acridinyl)bromoacetamide as a fluorogenic labeling reagent in an aqueous-organic two-phase system, gives esters with very high fluorescence intensity. The radiochromatographic method makes use of on-line radioactivity monitoring of the substrate and product in order to follow the hydrolysis reaction. In both methods reversed-phase liquid chromatography is used. A method for the synthesis of 3H-labeled choline esters is also described. Both techniques are compared with regard to sensitivity, reproducibility and practical considerations.

N-(9-acridinyl)-bromoacetamide--a powerful reagent for phase-transfer-catalyzed fluorescence labeling of carboxylic acids for liquid chromatography

Phase-transfer-catalyzed esterification of various carboxylic acids has been carried out on a microanalytical scale with a new reagent, N-(9-acridinyl)-bromoacetamide, in aqueous/organic two-phase systems. The procedure gives esters showing very high fluorescence intensity in acid solution. The large Stokes' shift (greater than 120 nm) means that a low background can be achieved even when using a large emission bandwidth. These derivatives show very good chromatographic behavior on reversed-phase liquid chromatographic columns with the use of aqueous acetonitrile, containing 0.2% of phosphoric acid, as the mobile phase. Detection limits (S/N = 2) as low as 10 fmol can be obtained under optimal conditions.