Methods for the detection of polar organophosphonates like the herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) in seawater were developed within this thesis. These compounds are difficult to measure in saltwater because salt matrix ions hamper their enrichment and instrumental analysis. Matrix effects were successfully reduced through sample desalination with electrodialysis. Moreover, glyphosate and AMPA could be enriched from seawater with a salt-insensitive molecularly imprinted polymer. This approach enabled the first detection of glyphosate and AMPA in seawater.