Optimization of NMR analysis of biological fluids for quantitative accuracy

With the rising interest in the use of nuclear magnetic resonance (NMR) for the study of biological fluids such as urine and serum for metabonomic or diagnostic purposes, new challenges have arisen concerning the efficacy of NMR data acquisition and analysis. In particular the quantification of sample constituents such as metabolites is of great importance. This study compares five one-dimensional proton NMR pulse sequences using synthetic urine samples to determine appropriate acquisition parameters for reasonable sample throughput and accuracy. Each pulse sequence has its own advantages and limitations with respect to solvent suppression, stable baseline, exchangeable protons, and quantization of resonances near the residual water peak. Hardware issues such as low-pass filters, unique to each spectrometer, also impact quantitation accuracy. Metabolite concentrations were determined using integration referenced to an added internal standard, and using the Chenomx NMR Suite software package. Since nuclei in different metabolites and the internal standard all have different longitudinal relaxation rates (T1) we included a mathematical correction factor for quantitation.