Methodological aspects of methylphosphonic acid analysis: Determination in river and coastal water samples

Methylphosphonic acid (MPn) is suspected to play an important role in aquatic systems like rivers or the open ocean. To gain more insights into the importance of MPn, e.g., for the aquatic phosphorus cycle, an analytical method for its quantitative determination was developed. The method is based on the use of an isotopically-labelled internal standard and sample preparation including solid-phase extraction (SPE). Instrumental detection was done using GC-MS after derivatisation of MPn with N-tert-Butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA). The study compares different isotopically-labelled compounds as well as different SPE-materials. As water samples with high salt content decrease the recovery of the chosen SPE-material, a desalting procedure using electrodialysis was implemented. Finally, water samples from different aquatic systems located at the German Baltic Sea coastal area were analysed to gain first insights into the relevance of MPn in these systems. MPn-concentrations in the low μg/L-range were detected.