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Research paper : Expansion of organic reference materials for the analysis of hazardous substances in food and the environment (T. Ihara et al.)−24−Synthesiology - English edition Vol.2 No.1 (2009) improvements are needed for the commercialization of this technique.9 Reason for using deuterated solventsQuestion and comment (Akira Ono)You noted in section 4.2 that you used a deuterated solvent. Can you explain why you used deuterated solvents for quantitative NMR? Should we infer that using 1H (proton) solvents disable quantitative NMR?Answer (Toshihide Ihara)In our study, 1H was used as the measurement nucleus. When solvents contain 1H or protonated solvents are used, the 1H signals from the solvents become much stronger than those from the compounds intended to be observed. As a result, the dynamic range of an instrument may prevent the accurate measurement of the analyte signal. Deuterated solvents are used to minimize the 1H from the solvents to resolve this problem. This is, in general, not just for quantitative NMR, but is also for conventional 1H NMR measurements.On the other hand, in the international comparison of ethanol, aqueous solution was used, and the solvent in this case was protonated water (H2O) rather than deuterated water (D2O). Therefore, the problem of dynamic range may occur. In such case, the resonance frequency of the solvent (water) signal is irradiated selectively with low power radio frequency pulse to saturate this signal. This saturation pulse is immediately followed by a normal pulse. This approach, called the pre-saturation method, cancels the interference of a strong H2O peak. Although power applied to this saturation pulse is low, peaks resonating at nearby frequencies are influenced by the pulse. This may compromise the accuracy of the analytical value obtained in this method. In other cases, irradiation strength, duration, and other factors must be set correctly to obtain the accurate analytical values. For these reasons, it is simple and safe to use a deuterated solvent.Additionally, to maintain the stability of the magnetic field, resonance frequency of the deuterium signal from the solvent is monitored to adjust the strength of the magnetic field from time to time to maintain constancy of the signal frequency. This process is called a “deuterium lock.” Since NMR measurements, including quantitative NMR, tend to take relatively long time, deuterium lock is indispensable to obtain spectra of high resolution. If the sample solvent is not deuterated, deuterated solvent must be added.

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