Various species of aquatic cyanobacteria produce potent hepatotoxins, the microcystins and nodularins. Highly selective methods are essential for trace analysis of these substances in limnic sediments. This dissertation presents two approaches to attain the required selectivity. First, liquid chromatography/mass spectrometry was applied for selective detection of the toxins in complex sediment extracts obtained by ultrasonic extraction with organic solvents. In addition to known toxin

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... methylated variants of the parent compounds were identified in several extracts. Most likely, these derivatives were methyl esters, artefacts formed during prolonged storage of the methanolic sample solutions. Second, a novel and more selective extraction technique, electrokinetic sample extraction and enrichment (ESEE), was developed. Applying an electrical field to the wet sediments, various transport processes were induced inside the samples, in particular electroosmosis and electromigration. These mechanisms were used to transport the target analytes out of the samples. The toxins were simultaneously enriched online on solid phase extraction disks. After elution from the disks, the analytes were determined by high performance liquid chromatography with diode array detection. Analysing cyanobacterial toxins in organic-rich sediments from polytrophic Lake Federsee (Germany), ESEE was found to be a quite selective extraction technique. With a subsequent size exclusion chromatography (SEC) clean-up, ESEE allowed a dramatic selectivity enhancement of the sample preparation, compared to the combination of ultrasonic organic solvent extraction with SEC. Adequate recovery rates and good precision were achieved for several toxin congeners exhibiting different charge states and varying hydrophobicities. Microcystin-RR and -LR were detected in non-spiked samples from Lake Federsee at a concentration level in the order of 0.1 µg/mL, based on the volume of the wet sediments.