Quarternary Ammonium Salts for Butylation and Mass Spectral Identification of Volatile Organic Acids

Article abstract of DOI:10.1021/ac00257a004

The esterification method described by Greeley (J.Chromatogr. 1974, 88, 229) was modified to overcome the problem of volatile acid evaporation during sample workup procedures.After solvent extraction from an aqueous sample, the acids were converted to their butyl ester derivatives in a two step process.Firstly, an involatile quarternary ammonium salts was formed which allowed concentration by solvent evaporation without loss of volatile acids.The acid salts were then converted to butyl esters by heating in the presence of n-butyl bromide and the esters were separated on a support- coated open tabular (SCOT) OV17 capillary column.The recovery and butylation yield were shown to be quantitative for isobutyric acid and the linearities and limits of detection are given for the five C₄-C₅ aliphatic acids.The mass spectra of butyl esters contain abundant rearrangement ions not present in methyl, ethyl, trimethylsilyl, or aryl esters which enable their rapid identification.The method was applied to the analysis of volatile urinary acids from a patient with Maple Syrup Urine Disease and showed conclusively the presence of both 2-methylbutyric and isovaleric acids.