A gas chromatographic method was developed for the determination of the volatile and nonvolatile organic acids, as their butyl derivatives, in fruits.
The acids were extracted by 75% ethanol or hot water (for grapes). The aliquot was passed through ion exchange resins to eliminate the interferences. The eluate containing acids was neutralized by sodium hydroxide and evaporated to dryness under vacuum at 55°C. These sodium salts of organic acids were esterified with sulfuric acid and butanol, then the esters these prepared were extracted in hexane. The hexane solution of butyl derivatives including n-tridecane as an internal standard was separated on a column of 5% Reoplex 400 on Chromosorb W AW.
This method permits the simultaneous determination of several volatile and nonvolatile organic acids in fruits, such as formic, acetic, lactic, glycolic, oxalic, fumaric, malic, tartaric and citric acids within an hour.