ESI Single Quadrupole Mass Spectrometric Investigation of Polyhydroxy Acids

Abstract

ESI-MS spectra were recorded with a FIA-MS system under CID conditions for 19 polyhydroxy carboxylic acids to assess the analytical selectivity of single quadrupole MS and to evaluate its suitability for the qualitative identification of the target compounds. Suited ESI operation conditions were defined for several sugar acids and their lactones and the pH dependence of the respective acid-lactone conversion was investigated. Besides the common neutral mass losses of H₂O and CO₂ specific mass losses, presumably belonging to the release of small carbon chain units, were established for isocitric and gluconic acids. A product ion with m/z 75 was part of the MS spectra of all aldonic acids, potentially indicating this structural subgroup of sugar acids. The spectra of other sugar acids and of tartaric, isocitric and shikimic acids had a product ion with m/z 73 in common. The results reveal that the CID mass spectra of several hydroxy acids show characteristic product ion patterns suited for a selective analyte identification.

Keywords:

• Acid-lactone conversion
• Collision induced dissociation
• Polyhydroxy carboxylic acids
• Single quadrupole ESI MS
• Sugar acids
• Uronic acids

Notes

MS conditions, as not stated otherwise: needle temperature 500 or 550°C, needle voltage −3.0 kV, cone voltage (CV): −100 V.

Peak heights of the product ions related to the height of the [M-H]⁻ peak (=100%): g (greater): >100%, h (high): 50–100%, m (moderate): 25–50%, l (low): 10–25%.

*“?” denotes identification by mass loss not possible.