title: Improved high-performance liquid chromatographic analysis of some carboxylic acids in food and beverages as their p-nitrobenzyl esters.
abstract: An improved, straightforward and accurate method for the derivatization and quantitative high-performance liquid chromatographic analysis of carboxylic acids in food and beverages is presented. Thirty-two p-nitrobenzyl esters were prepared in high yields by direct reaction of the free acid with O-(4-nitrobenzyl)-N,N'-diisopropylisourea in dioxane-water (9:1). Benzylmalonic acid was used as a new internal standard. Excess of reagent was removed on a strong cation-exchange resin. The advantage of this original and very convenient procedure over the usual clean-up step involving filtration through a disposable silica cartridge is discussed. The p-nitrobenzyl ester derivatives were readily separated using a single linear gradient of solvent (acetonitrile in water). With a high-performance liquid chromatography column of conventional size (20-25 cm X 4.6 mm I.D.), the analysis lasted for less than 20 min. This analysis time was even shorter (less than 12 min) when using modern small-bore (100 X 2.1 mm I.D.) columns. Applications of the method to the analysis of the main carboxylic acids in coffee, wine and fruit juices are presented.
mesh_terms: D001593:Benzyl Compounds; D001628:Beverages / Q000032:analysis*; D002264:Carboxylic Acids / Q000032:analysis*; D002712:Chlorides / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D003069:Coffee / Q000032:analysis; D004952:Esters; D005504:Food Analysis; D005638:Fruit / Q000032:analysis; D007202:Indicators and Reagents; D009574:Nitro Compounds; D012997:Solvents; D014920:Wine / Q000032:analysis
chemical_list: D001593:Benzyl Compounds; D002264:Carboxylic Acids; D002712:Chlorides; D003069:Coffee; D004952:Esters; D007202:Indicators and Reagents; D009574:Nitro Compounds; D012997:Solvents