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.)−14−Synthesiology - English edition Vol.2 No.1 (2009) system is not unique to reference materials. However, it is different from the weight system in a number of ways.Figure 1 is a schematic diagram of the traceability system for the RMs used in the analysis of volatile organic compounds that are used to test the quality of river and tap water in Japan. The national RM is in the form of a single solution incorporating 23 volatile compounds. Traceability to SI is obtained using pure substances for each component that is valuated using the freezing point depression method. The secondary and working RMs also consist of a single solution incorporating 23 volatile organic compounds, but in this case, calibration from upper-order to lower-order standards is conducted separately for each component. Because the lower-order traceability system requires a one-to-one correspondence, the pyramid structure breaks down for these RMs. In other words, the national RM for a given component must be used to calibrate the secondary RM for the same component, and calibration of working RMs for the same component is performed using this secondary RM. Because this is one-to-one calibration of the same chemical compounds, commercially available analytical technologies such as gas chromatography can be used for calibration down to the working RM level while maintaining excellent reliability. This practical system of traceability is used throughout the world.The drawback of this traceability system is that it requires a wide array of national RMs to match each chemical compound subject to be analyzed. Development of these national RMs is a major bottleneck in the traceability system because it requires enormous time, labor, and expense. The construction of a more efficient traceability system based on an entirely new concept is needed to address the rapidly proliferating demand for RMs prompted by increasingly tight regulation of chemical compounds through the positive list system discussed above.3 Research target: Construction of an efficient traceability systemTo recapitulate the previous chapter, the problem with present traceability system for RMs lies in the dependence on national RMs. Because the system consists of the series of “calibration chains” for the same chemical compound, the system cannot respond promptly to the need for RMs to analyze the growing number of chemical compounds. Although this problem can be solved if minimum types of higher-order RMs could be used to calibrate a wide range of working RMs, this is not possible with current calibration technology, which is designed to calibrate like chemical compound with like chemical compound. An entirely new calibration technology must be developed and introduced: a universal calibration technology capable of analyzing chemical compounds independently of their molecular structure.The aim of this study is to develop a new calibration technology to realize a system that efficiently secures traceability to the wide range of working RMs without creating national RMs for each chemical compound. Given that the vast majority of chemical compounds subject to strengthened regulation in recent years are organic compounds, we developed a universal calibration technology targeting organic compounds.4 An analytical method that achieves our objectives: Quantitative NMR4.1 The required calibration technologyAbsolute values for amount-of-substance can be obtained using SI-traceable measurements. This type of measurement is known as the primary method of measurementTerm 6, [2]. Table 1 shows a list of analytical methods certified as primary methods of measurement, divided into primary direct methods and primary ratio methods. The primary direct methods, also called the absolute measurement methods, are defined as “the methods for measuring the value of an unknown without reference to a standard of the same quantity.” Examples of primary direct methods are coulometryTerm 7, gravimetryTerm 8, and the freezing point depression methodTerm 9. Because these analytical methods yield absolute values for amount-of-substance, they are appropriate for valuing the national RMs. However, in general, they tend to be slow and their application are limited to short list of substances, and they are not suitable candidates as universal calibration technology that is the objective of this study. Primary ratio methods, on the other hand, are already in practical use. They are defined as “methods for measuring the value of a ratio of an unknown to a standard of the same quantity; its operation must be completely described by a measurement equation.” They include titrimetryTerm 10 and isotope dilution mass spectrometryTerm 11. Another analytical approach that qualifies as a primary ratio method, though not well established as an analytical technology, is the quantitative nuclear magnetic resonance (quantitative NMR).with 15 othercomponentsbenzeneotoluenebromoformchloroformdichloromethaneCalibration of pure substances using the freezing point depression method;preparation of 23 mixed standard solutionsCalibration of identical components using gas chromatographyWorking RMSecondary RMNational RMDefinition of SI (amount-of-substance)-xylene-xylene-xylenepm0with 15 othercomponentsbenzeneotoluenebromoformchloroformdichloromethaneCalibration of identical components using gas chromatography-xylene-xylene-xylenepm0with 15 othercomponentsbenzeneotoluenebromoformchloroformdichloromethane-xylene-xylene-xylenepm0Fig. 1 Traceability system for RMs used in analysis of volatile organic compounds.

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