Expanding the Analytical Window for Amino Acids in Marine Particles through tandem LC-MS

Amino acids have long provided important information on the cycling and degradative state of marine organic materials. Traditional methods of characterizing the amino acid fraction of organic matter, however, often requires a lengthy derivitization process, significant sample amounts, and are limited to a subset of the 20 biosynthetic amino acids, or specialized to determine modified structures. Taking advantage of the high sensitivity and mass accuracy of chromatography tandem mass spectrometry, UHPLC methods were developed to allow quantification of more than 45 amino acids from varied sources in a single analysis. By using an ion pairing reagent and deuterated internal standards, derivitization is not required and identification can be made at low pM limits of detection and high precision. Comparisons of this approach to the recent use of GC/MS suggests that the use of LC/MS lowers the limit of detection by up to 10 fold and expands the suite of compounds with similar precision. This method is being used to investigate varied environmental questions including amino acids as osmosis regulators in sea grasses and broader analysis of POM samples gathered in the Arctic Ocean. The results of a suite of sample types examined thus far show low limit of detection and high precision independent of the matrixes complexity. Initial analysis of marine diatoms and of heterotrophic marine bacteria show significant amount of thio-proline, sarcocine and arginine not seen in GC/MS measurements. Sarcosine is an intermediate in the synthesis of glycine and arginine is an important player in the urea cycle while the role of thio-proline is under investigation. This approach adapted for marine systems makes it possible to characterize a broader suite of amino acids which can be important measures of the carbon and nitrogen cycle.