Validation of 1H NMR spectroscopy as an analytical tool for methylamine metabolites in urine

Background: Methylamines have many metabolic roles and there is an increasing demand for their measurement. Glycine betaine is an important osmolyte, and a reservoir for methyl groups. Proline betaine and trigonelline are important dietary betaines. Trimethylamine, derived from gut flora, is normally converted to trimethylamine oxide but in 'fish odour syndrome' is excreted as TMA. These compounds are all suitable for quantification by H-1 NMR spectroscopy as they all have methyl protons. Method: Urine samples are acidified and H-1 NMR spectra are obtained using presaturation for water suppression. Peak integrals or heights are compared to an internal standard of acetonitrile. Results: Inter- and intra-assay CV's were < 5% for TMAO and creatinine, and < 10% for the other analytes. Responses were linear from 50 to 1000 mu M for all metabolites, and recoveries were >= 97%. Limits of detection using NMR are slightly higher than alternative HPLC assays (15-25 mu M). However, sensitivity is adequate for the detection of raised levels in urine, and sample analysis was complete in less than 5 min. Conclusion: H-1 NMR spectroscopy is a convenient, rapid and economical option for the determination of betaines and related compounds in urine in a single analysis. (c) 2005 Elsevier B.V. All rights reserved.