Abstract
A LC‐MS/MS method with enhanced sensitivity and specificity was established for monitoring microcystin‐LR (MC‐LR) in drinking water supplies in southern Taiwan. The enhanced sensitivity was achieved by the selection of a doubly charged MC‐LR as the precursor ion to result in an multiple reaction monitoring (MRM) pair ions of m/z 498.6 → 135.0. Using this ion pair, a record low detection limit of 2 pg was achieved on column, found in the available literature. A sample preparation method involving C8 solid‐phase extraction gave satisfactory recoveries of the analyte. Nodularin, with structural similarity to MC‐LR, was used as an internal standard to minimize matrix effects of water samples collected from six different water reservoirs in southern Taiwan, where MC‐LR was detected at sub‐ppb levels in all the reservoirs. The best precision and accuracy of this method were found with samples prepared to contain MC‐LR at 0.1 and 1 µg l^−1^. This new method requires considerably smaller water sample volumes because of enhanced quantification sensitivity and hence reduces the time needed for analysis. It should serve as a useful example for method development for monitoring other members of the microcystin family in drinking water supplies. Copyright © 2006 John Wiley & Sons, Ltd.