Effect of magnesium ion in the analysis of carboxylated compounds by electrospray-mass spectrometry Original Research Article

The divalent magnesium ion generates various adducts with low-molecular-weight carboxylated compounds (e.g. propionic acid) in the analysis of aqueous solutions by electrospray ionization mass spectrometry (ESI-MS). The adducts detected correspond to singly charged cluster ions of magnesium with the general formula (MgnL2n+1)−, where L represents the different anions in solution. Mono-functionalized compounds, such as propionic acid, mainly formed dinuclear complexes, whereas poly-functionalized compounds, such as glutathione, generated significant amounts of mononuclear and other types of polynuclear complexes, in addition to dinuclear complexes. An equimolar mixture of five carboxylic acids (propionic-heptanoic) with magnesium chloride gave numerous peaks distributed in the 300–1000 m/z range in five Gaussian-shaped groups, each representing gas-phase ions with a particular molecular formula. We propose a statistical approach which explains that the Gaussian distribution of peaks arises from the various combinations of different fatty acids required for a specific molecular formula for a particular gas-phase cluster.