Determination of small carboxylic acids by ion exclusion chromatography with electrospray mass spectrometry

Ion exclusion chromatography (IEC) is used with electrospray mass spectrometry (ES-MS) to analyze a mixture of formic, glyoxylic, oxalic, 2-hydroxyisobutyric, and maleic acids. Compromise experimental parameters were evaluated. Ion extraction voltages can be found that produce reasonable signals from negative parent ions ([MH]−) of these compounds as well as succinic, malic, 1-hexanoic, malonic, and tricarballylic acids. The effects of sheath gas, solvent composition, concentrated matrix ions, and pH of solution on sensitivity and linearity were examined. A basic isopropanol solvent with nitrogen sheath gas yield the best results. Detection limits are 40–200 ppb for direct infusion of sample into the ES-MS and 2–8 ppm for IEC-ES-MS. The presence of concentrated matrix ions can suppress the analyte signal significantly. These matrix effects are minimized by Chromatographic separation and internal standards. In most cases, the sample is injected directly onto the column with little or no preparation. A small additional flow of organic solvent with pH adjustment is added before the sample reaches the ES-MS.