Fresh Dual Presaturation Method for Analyzing HO-Rich Samples Using Quantitative H NMR.

A fresh dual presaturation (pre-SAT) method was developed to quantify analytes accurately near the suppressed water signal in H NMR spectra obtained from HO-rich samples. The method includes an extra dummy pre-SAT with a suitable offset for each analyte signal in addition to the water pre-SAT. The residual HOD signal at 4.66 ppm was observed using DO solutions containing l-phenylalanine (Phe) or l-valine (Val) and an internal standard of 3-(trimethylsilyl)-1-propanesulfonic acid- sodium salt (DSS-). When the HOD signal was suppressed using the conventional single pre-SAT method, the measured concentration of Phe from the NCH signal at 3.89 ppm decreased by a maximum of 48%, whereas the dual pre-SAT method gave a reduction in the Phe concentration measured from the NCH signal of less than 3%. The proposed dual pre-SAT method achieved accurate quantification of glycine (Gly) and maleic acid (MA) in a 10 vol % DO/HO solution. The measured concentrations of Gly of 513.5 ± 8.9 mg kg and MA of 512.2 ± 10.3 mg kg corresponded to sample preparation values of Gly of 502.9 ± 1.7 mg kg and MA of 506.7 ± 2.9 mg kg (the number after "±" indicates the expanded uncertainty ( = 2)).