In the chemistry field, reference materials that are “homogeneous and stable with their properties accurately determined within the range of uncertainty” are used for calibration of analytical equipment and quality control of analysis. With rising public awareness of the importance of a clean environment, health, and safety, the demand for reference materials essential for accurate analysis is growing rapidly. Reference materials developed and provided by NMIJ in this area are roughly divided into three categories: 1) materials that serve as the basis of chemical measurement, such as standard gases, inorganic standard solutions, and organic standard solutions, which are supplied as reference materials accredited by the Japan Calibration Service System (JCSS); 2) matrix reference materials prepared from natural samples, such as sediments, essential for analytical quality control for items regulated by environment laws (heavy metals, PCBs, etc.); and 3) standard materials related to advanced materials necessary to support state-of-the-art industrial processes. International comparisons are held very frequently in this field under the Consultative Committee for Amount of Substances (CCQM) of the International Committee for Weights and Measures. We participate in most of such opportunities to demonstrate and maintain our high analytical capability at international level.    

In inorganic analysis, the use of elemental standard solutions with known concentrations is essential, whether the subject to be analyzed is an industrial material or an environmental sample. These concentration values must be based on common measures, i.e., the SI, wherever they are used. To realize primary standards that comply with the SI, NMIJ uses various methods, including titration, gravimetric analysis, or coulometric titration, which can be a primary method of measurement (method recognized as being particularly accurate) to study purity-determination methods of raw materials for elemental standard solutions and concentration-measuring methods of elemental standard solutions.
Many kinds of metal ions form chelate complexes with a chemical compound named ethylenediaminetetraacetic acid (EDTA) at a ratio of 1:1. Using this property, it is possible to make accurate comparison of concentrations of metal standard solutions of either the same or different kinds according to the titration method. Gravimetric analysis allows accurate determination of the amount of substance (mole) through accurate measurements of mass. Coulometric titration uses Faraday's Law to determine the amount of substance from electrical quantity, mass, and time. Since either of these two methods is an extremely good technique, and since there is no need to use reference materials, we have been studying them as techniques for determining the purity of raw materials such as some kinds of salts or oxides. These techniques are also applied to the establishing of primary standards for anion standard solutions.     �iInorganic, Standards Section�j

With the interest in global environment growing, the demand for determination of trace and ultratrace components is also expanding in the field of environmental analysis. Chemical analysis is being sought after at ever higher levels of accuracy. NMIJ is engaged in the development of accurate quantitative analytical methods for trace components in environmental samples and of matrix reference materials (i.e., reference materials whose matrix compositions similar to actual environmental samples, such as sediment or soil, are certified), which is essential to secure the reliability of environmental analysis.
NMIJ has developed two marine sediment certified reference materials (NMIJ CRM 7301-a and NMIJ CRM 7302-a), shown in the photo. Both were prepared from the sea bottom at two locations off northern Kyushu through processes that included drying, pulverization and mixing. For NMIJ CRM 7301-a (for analysis of butyltins), the contents of three kinds of butyltin compounds are certified. For NMIJ CRM 7302-a (for analysis of toxic metals), the contents of 11 elements, including antimony (Sb), arsenic (As), and cadmium (Cd), are certified.     [ Environmental Standards Section ]

Standard gases include high-purity standard gases and standard gas mixtures. The former are gases that contain only one species, such as pure nitrogen or pure nitrogen monoxide, and are used as starting materials for standard gas mixtures. NMIJ measures the purity of pure gases using various analytical techniques. The latter contain prescribed concentrations of component gases. NMIJ and the Chemicals Evaluation Research Institute (CERI) have developed 10 types of inorganic and 14 types of organic standard gas mixtures. These standard gas mixtures are binary ones and prepared by diluting high-purity raw materials with nitrogen or synthetic air. Concentrations of standard gas mixtures are calculated from mass ratio of each component weighed with a high-precision balance, as shown in the photo. This method is called the gravimetric blending method that is one of the primary methods to obtain a traceable standard to the SI units.     [ Gas Standards Section ]

The Organic Standards Section has completed the development of organic standard materials for neat liquid of 23 VOCs (volatile organic compounds), including trichloroethylene and benzene, which are used as starting materials for standard solutions currently planned to be supplied under JCSS. These VOCs are well known to contaminate large areas of air, water and soil. The section also plans to provide standard solutions of 10 chemical materials, which are suspected to be endocrine disrupters. These standard solutions will also be accredited by the JCSS. NMIJ has developed ethanol, benzene, toluene, o-xylene, ethylbenzene, and 1, 2-dichloroethane as the NMIJ Certified Reference Materials (NMIJ CRM) and has started providing them to users. The photo shows the NMIJ-CRMs of high-purity VOCs filled in 15-ml ampoules.     �iChamical Analysis Standards Section�j

In addition to the upgrading and development of measuring techniques, development of reference materials is also necessary to make accurate measurements of molecular weights of high polymers, such as plastics, and the contents of additives. NMIJ is working on the development of reference materials for measurement of molecular weights of polymers such as polystyrene or polycarbonate, and plans to develop other reference materials for molecular weights and additives. We are currently working on quantitative analysis using NMR, analysis of additives, mass spectrometry of polymers and improvements to the accuracy of light-scattering measurements. R&D of nanoparticle reference materials has just begun to back up nanotechnology development. Organic compounds have their own "spectra," like human fingerprints, and therefore we can identify unknown materials by collating the spectra of those materials against known spectra stored in our database. The spectra database SDBS for organic compounds is accessible at no charge on the Internet and is frequently visited from all over the world (http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi).     �iMetrological Information Section�j

Technical advancements in the biotechnology field are outstanding, but the discussion on standardization of analytical techniques or analyzers has just started. In reply to the issues raised about the SI traceability or international consistency for analytical values in the bio field, the Consultative Committee on the Quantity of Materials (CCQM) of the International Committee of Weights and Measures (CIPM) reviewed the issue from the metrological viewpoint and set up the Bio Analysis WG as the sixth WG of CCQM in April 2001, The DNA determining method was selected as the subject for the first international comparison (pilot study) and preparation of test samples is currently ongoing. NMIJ intends to participate in this international comparison. The Joint Committee on Traceability in Laboratory Medicine (JCTLM) was established jointly by the CCQM and the International Federation of Clinical Chemistry in June 2002 to guarantee traceability in the pharmaceutical area of the bio field. In this way, there is a rapidly developing movement in the fields of biotechnology and clinical analysis to accept a metrological approach including uncertainty evaluation. In order to catch up with the accelerating changes in bio-related standards, NMIJ intends to actively support the bio standard field in close cooperation with the Ministry of Economy, Trade and Industry, related organizations, and the relevant departments and centers of NMIJ.     [ Bio-Medical Standards Section ]

Surface chemical analysis is a pivotal technique for materials development and materials quality control in advanced industries, including the information industry. Testing methods using these analytical techniques need to be standardized. NMIJ has developed multilayer reference materials that have steep interfaces for optimization of depth-profiling analysis. Figure 1 shows the structure of our GaAs/AIAs superlattice multilayer certified reference material, whose supply has just begun. The thickness of each layer is about 24 nm and thickness uncertainty is about 0.3 nm. Given such extremely small uncertainty, this reference is capable of ensuring atomic-level precision. The X-ray reflectivity method was used to measure the thickness of these layers. Our method features a level of precision equivalent to an absolute evaluation method in terms of the thickness of thin films or multilayer films and is also expected to provide information on density or surface and interface roughness. Figure 2 shows a depth profile of the reference material that is carried out by using Auger electron spectroscopy. It is capable of observing subtle changes in the interfacial profile, thereby enhancing the precision of depth-profiling analysis.     [ Surface and Nano-Analysis Section ]

Use of an electron probe microanalyzer (EPMA) allows relatively easy qualitative and quantitative analysis of elements for micron-order areas without complicated sample pre-treatment. Therefore, the EPMA technique has been widely applied to R&D and product control of various kinds of inorganic materials, including metals. Reference materials are crucial for high-precision quantitative analysis by EPMA. Since the EPMA is a microprobe analyzer, reference materials used for this device are required to ensure particularly stringent concentration homogeneity. The Surface and Thin Film Standards Section have established a method for evaluating in-plane homogeneity using EPMA and use these methods to develop certified reference materials. Evaluation results of detailed homogeneity directly help to evaluate uncertainty and clarify what to improve in preparing samples and therefore contribute to further improvement of concentration homogeneity. Details of reference materials planned to be developed and element concentration are shown below.

The National Metrology Institute is making preparations to develop nano scales in the depth direction applicable to measurement of nano profiles and structures. As one of the next-generation measurement standards, such highly precise nano scales are required to play an essential role in accelerating the shrinkage in size of devices, including semiconductors. The nano scale also forms the most basic foundation of nano metrology. Nan0 scales targeted by the NMIJ are those 10 nm or under in the depth direction. For porous materials, the Nanopore Standards Section is working on the size evaluation of pores using such methods as positron annihilation and on development of nanopore standard materials.     [ Nanomaterial Characterization Division ]

The Metrological Statistics and Particle Measurement Section is engaged in developing measurement methods of fine particles and powders, and related standard reference materials. The electro-gravitational aerosol balance developed in this section, which makes use of the temporal change in the number of charged particles confined in a closed space under the influence of electrostatic and gravitational forces, is a device for absolute size measurement of monodisperse particles. The uncertainty of 100 nm particle measurement by this device is 0.66 nm in terms of the expanded uncertainty with coverage factor of 2.     �iParticle Metrology Section�j