Vol.2 No.1 2009

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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.)−17−Synthesiology - English edition Vol.2 No.1 (2009) conventional analytical calibration technologies applied in the international comparison can only be used to compare the concentrations of like chemical compounds (PS must be the same chemical compound as the measured substance), quantitative NMR can compare quantities of chemical compounds of different types (that is, PS does not have to be the same type of chemical compound as the measured substance). As such, although quantitative NMR requires at least one substance including 1H, it can be used to measure any organic compound that includes proton, and a wide range of applications can be expected accordingly. The Authors believe that quantitative NMR can be applied in the calibration of working RMs by developing and integrating certain elemental technologies. These are discussed below.5 Development and integration of elemental technologies to realize the quantitative NMR5.1 Core elemental technologiesFigure 6 illustrates the elemental technologies developed by the authors, and the combination necessary to realize the potential of quantitative NMR as a universal calibration technology for working RMs. The features required of NMR differ greatly depending on whether the technology is optimized for qualitative analysis or for quantitative analysis, as in our case. With quantitative NMR, the highest priority is to observe the signal in accurate proportion to the number of atomic nuclei in the analysis, rather than improving measurement speed or improving the signal-to-noise ratio (S/N). We therefore revised the conditions for selecting the core elemental technologies.The first elemental technology corrects a signal amplification issue. Generally speaking, NMR signals relax throughout its lifetime called the spin lattice relaxation time (T1), which is the time taken for the atomic nuclei to settle from their excited state to their ground state. This period varies according to the environment of protons (such as bonding with other atoms). When NMR is performed for qualitative analysis, the sample is irradiated with microwave pulses with short cycle to increase the signal and to improve S/N. In such case, the delay time may be shorter than T1, where excitation pulse is applied before all protons settled to their ground state. As result, differences in T1 among the protons of analyte and PS make it impossible to obtain the peak area in correct proportion for the number of protons in each proton. We resolved this problem by measuring the relationship between repetition time and peak area. By taking delay time six times or greater than T1 for the analyzed protons, it was demonstrated by experiment that 99.9 % or more of original signal intensity could be obtained, providing a stable peak-area ratio[5]. By ensuring that the delay time was sufficiently longer than the longest T1 for all protons in the analyte, it was possible to obtain accurate peak-area ratio that was unaffected by the T1 of the protons (though the measurement time increased several times longer than the conventional method).The second elemental technology also concerns the S/N. Normally, S/N in the NMR signal is further improved by using an audio filter to narrow the bandwidth. However, this filter is not “flat” in sensitivity throughout the bandwidth, but exhibits severe loss of sensitivity at both ends of the filter bandwidth. Depending on the chemical shift, this loss of sensitivity can be in the range of several percents. Greater the chemical shift in the protons observed in the analyte and PS, more difficult it is to obtain an accurate peak-area ratio. To obtain flat sensitivity, we set the audio filter to cover 60 %~70 % of bandwidth and also widened the spectral width for data acquisition to 100 ppm, compared to less than 20 ppm in the conventional setting. This setting allowed the resulting spectrum to remain unaffected by sensitivity loss caused by filter for all chemical shifts. While such filter settings are not practical for ordinary NMR that involves handling of large volume data, we were able to solve several issues by taking an unconventional Development and integration of elemental technologiesApplication of resultsCalibrationDisseminationCalibrationCalibrationCalibrationConfirmation of equivalenceof analytical value(product realization research)Future issues ■ Optimization of delay time ■ Optimization of audio filter ■ Improvement of phase correction ■ Improvement of baseline correction ■ Stabilization of integration settingCore elemental technologiesTransfer materialQuantitativeNMRinstrumentQuantitative NMR technique(Qualitative) NMR techniqueAnalysis at inspection, testingand research laboratoriesWorking RMNational RMPurity determination by freezingpoint depression methodApplication of resultsFig. 6 Development of elemental technologies for the construction of universal calibration technology and the process of integration.

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