Sensitive determination of total microcystins with GC-MS method by using methylchloroformate as a derivatizing reagent

Various microcystins (MCs) produced by cyanobacteria pose a potential threat to water resources, therefore, the determination of the total MCs rather than the content of some specific types of MCs in water is of great importance. Oxidation of MCs causes cleavage of the Adda moiety of microcystins to 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB). In this paper, a new method based on the derivatization of MMPB with methylchloroformate is proposed for the sensitive determination of total MCs. The oxidation conditions as well as the esterification process were optimized through a series of batch experiments. With the optimized procedure, a detection limit as low as 0.56 mu g L-1 was achieved for total MCs and the method was successfully applied to the determination of MCs in real samples. A comparison study by using the LC-MS method for direct quantification of the MMPB was also conducted to validate the proposed method. The results proved that the technique is highly sensitive and convenient for the quantification of total MCs in water samples. As an additional feature, the method does not require the use of toxic and expensive standards of MCs in the environmental monitoring.