Iron interference on matrix-assisted laser desorption/ionisation time-of-flight mass spectra of condensed tannins

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was used to reveal the influence of iron on the detectability of condensed tannins extracted from Picea abies. Iron chloride mixed with condensed tannins suppresses the detection of tannins by MALDI-TOF MS in a dose-dependent manner. Total suppression is observed at concentrations of 250 and 500 mg FeCl₃ g^–1 of sample. At lower concentrations, spectrum quality is still greatly reduced, but short chain tannins are detected. At 100 mg FeCl₃ g^–1 of sample, iron increased the intensity of the tannin galloyl ester peaks above those of the corresponding tannin polymers. This points to an antagonistic effect of the galloyl ester moiety on iron complexation with condensed tannins and, thus, their reduced susceptibility to iron interference during MALDI-TOF MS.