Quantitative analysis of cyanobacterial toxins by matrix-assisted laser desorption ionization mass spectrometry

Microcystins (MCs) are a growing problem in drinking water supplies worldwide. Common analytical techniques used to determine MC concentrations have several shortcomings, including extensive sample handling and lengthy analysis times. A simple, rapid method for quantitation of MCs by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is presented. Four potential internal standards were tested, including an 15N-labeled MC. For MC-LR in mixed standard solutions, a linear range of 0.11-5.0 microM (R2 = 0.98) was achieved, with a method detection limit (MDL) of 0.015 microM. Matrix effects due to extracted cell components decreased the MC-LR linear range slightly to 0.19-5.0 microM (R2 = 0.99), with MDL = 0.058 microM. Extensive analysis of possible internal standards indicates that nodularin was preferred over [15N]10-microcystin-YR or angiotensin I. The ionization efficiency and analyte-analyte suppression for four MCs of varying polarity are presented; the three polar congeners exhibited good ionization efficiency and acceptable levels of analyte-analyte suppression. These results indicate that MALDI-TOF MS represents a viable alternative for the quantitative measurement of MCs in field samples.