Analysis of microcystins in sediments using MMPB method.

During the course of study on the detoxification of microcystins, the adsorption on sediments in the natural environment was investigated. Because it was very difficult to extract microcystins from sediments using conventional techniques, a physicochemical screening method, the MMPB (2-methyl-3-methoxy-4-phenylbutyric acid) method, including ozonolysis and mass spectrometric detection was developed. This method consisted of the following operations: lyophilized sediments were suspended in methanol and MMPB-d(3) as an internal standard was added to this suspension, which was cooled at -78 degrees C with vigorous stirring and then treated with a stream of ozone/oxygen. After centrifugation, an aliquot of the reaction solution was subjected to EI (electron ionization)-GC/MS analysis after methylation with 14% BF(3)-methanol and liquid-liquid extraction. The established method had a potential for the analysis of microcystins in sediments that are difficult to analyze using conventional methods. Finally, this method was applied to sediment samples collected in Japanese lakes and six of the eleven samples showed positive results. The obtained results clearly indicated that the adsorption on sediments contributes to the detoxification of microcystins under natural conditions.