An HPLC Method to Quantify S-Methylmethionine in Marine Samples

S-methylmethionine (SMM) is a primary precursor to dimethylsulfoniopropionate and a derivative of the amino acid methionine; therefore, it serves as an important intermediate in the organosulfur cycle. A simple method was developed to quantify SMM in marine samples using precolumn derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid followed by separation using reversed phase high performance liquid chromatography (HPLC) with fluorescence detection. The method was adapted from published methods for SMM detection in non-marine samples. Several parameters were tested to develop and optimize the method including reaction pH, reaction time, and derivative stability. The detection limit of the method is approximately 0.5 nM with variation depending on the sample matrix and injection volume. Applications of this method to the analysis of northern Gulf of Mexico and estuarine water samples, macroalgae, cultures of marine phytoplankton, and salt marsh plants (e.g. Spartina alterniflora) will be presented along with a discussion of the importance of SMM to the marine organosulfur cycle.