A Technique for the Determination of Trimethylamine-N-oxide in Natural Waters and Biological Media

Trimethylamine-N-oxide (TMAO) is a nitrogenous osmolyte widely distributed in marine organisms. The reduction of TMAO to TMA has long been implicated as characteristic reaction associated with fish and seafood spoilage. However, it is now apparent that, in the marine environment, TMAO can act as precursor to a range of reduced nitrogenous biogases that can play a significant role in the biogeochemical cycle of nitrogen and in the regulation of atmospheric pH. Although methods exist for the analysis of TMAO in some biological samples, they lack the sensitivity required for measurement of TMAO in natural waters. Here we present a new, safe and sensitive method for the determination of TMAO in aqueous and biological media, where TMAO is enzymatically reduced to TMA and subsequently quantified using Flow Injection Gas Diffusion-Ion Chromatography (Gibb et al. J. Autom. Chem. 1995, 17 (6), 205−212). The limit of detection was calculated to be 1.35 nmol dm-3 TMAO, and the response was linear for both fresh and seawater (R 2 = 0.996 and 0.993, respectively). Precision (RSD) for standards in the range 40−600 nmol dm-3 was within 3%. The specificity and competitive inhibition of the enzyme are addressed and the applicability of the technique demonstrated through analysis of a number of natural water and biological samples.