Developments of Environmentally Certified Reference Material From the Brazilian Metrology Institute to Support National Traceability

Certified Reference Materials

Certified reference materials (CRM) is one of the essential pillar of metrology in chemistry, as its use is an important tool in the implementation of various aspects of measurement quality and confidence. Another important observation is environmental legislation, that has significantly increased, and which requires international standards of comparison. These standards are essential to the realization of the SI units and, therefore, are indispensable for establishing traceability of measurements. Inmetro is mainly responsible for keeping the national metrological standards of reference, as well as for carrying and spread the SI units of measurement, and its harmonization on a global level, providing traceability to a large number of users via a metrological chain.

According to the International Organization for Standardization (ISO) definition (ISO Guide 30, 2008), a reference material (RM) is a material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process. A RM can be either a pure substance or a mixture of components. Certified Reference Material (CRM) is a reference material characterized by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability. One or more parameters of a CRM can be determined and confirmed according to a specific procedure. To each certified parameter an uncertainty should be assigned at a given confidence level. Certificates are issued by recognized bodies.

The production is performed according to the ISO 17034 (ABNT NBR ISO 17034, 2017) and ISO Guide 35 (ABNT ISO Guia 35, 2012) and includes studies of homogeneity, stability and characterization, and its respective estimation of uncertainties. The evaluation of the homogeneity is particularly important in cases where the substance to be measured is present in a complex matrix. The stability study is divided into short-term and long-term stability studies. The first simulates the conditions of transport and should address the factors involved at this stage that can affect the CRM, such as temperature and time. The results of this study show that the form of transport and packaging are appropriate to the material. In the study of long-term stability is developed to assess whether the material is stable during its period of validity conditions of storage. The variations observed during this period in the amount of the certified properties should be included in the determination of uncertainty. At the stage of characterization may be used the following methods: a primary method, two or more independent methods on a same laboratory, or by an interlaboratorial comparison using one or more validated methods of accuracy. These guides may provide the basis for future assessment of reference material producers.

So, the use of CRM ensures that the results obtained by different laboratories are comparable and traceable. In this context, CRM are essential in maintaining a system of universal and consistent measurements make it possible to compare the measured values from one laboratory to another, besides disseminating traceability among society.