Identification and quantification of new isomers of isopropyl-malic acid in wine by LC-IT and LC-Q-Orbitrap

Organic acids of wine comprise one of the main taste groups, that of sourness. Two isomeric compounds with molecular weight of 176μ have been identified in wine using two LC-MS systems, LC-IT (ion trap) and LC-Q-Orbitrap. The two isomers are organic acids, 3-isopropylmalic acid (3-IPMA) never identified in wines, and 2-isopropylmalic acid (2-IPMA), never quantified in wines. After the definitive identification against the authentic standards, an analytical method for their determination in wines was optimised and validated using the LC-IT platform. Linearity was verified in the range 5–320mgL⁠−1 (correlation coefficients higher than 0.9914) and the recoveries obtained spiking the samples at two fortification levels were higher than 86.7%, with RSDs (n=9) lower than 15.1%. Finally, the two compounds were quantified in ten red and white Italian wines, and average concentrations were determined at 1.78mgL⁠−1 (0.56–4.13) and 23.0mgL⁠−1 (6.7–41.6) of 3-IPMA and 2-IPMA, respectively.