Preparation and characterization of a mussel reference material (Perna perna)

Abstract

The demonstration of the quality of analytical results and their adequacy to their intended use is becoming more and more an essential requisite to the quality assurance of products and processes, in the fields of industry, commerce, as well as applied research and it can affect, for instance, economical decisions and environmental protection policies such as the implementation of limiting values for pollutants and planning of corrective actions. One effective way of demonstrating the quality of analytical results is the comparison of the obtained result for a real sample with an assigned result for a well known material ,the Reference Material ,RM , which possesses sufficiently homogeneous and well established values of a given property. The RMs are used for the validation of analytical methods, in interlaboratory studies and proficiency tests and in quality assurance procedures, such as statistical control of processes in which control charts are utilized. When the values of the properties of RMs are certified by a procedure which establishes the traceability of these values to the exact value of the SI unit in which the values of the property are expressed, accompanied by an uncertainty at a given established confidence level, the RM is designated as certified reference material, CRM. Despite its importance in the quality assurance of analytical results,the use of CRMs is not as disseminated as it should be. In general, the complexities involved in the preparation and characterization of CRMs makes their price quite elevated, which makes their use not feasible economically for many laboratories. Besides,there are sometimes restricitions and difficulties involved in importing these materials. Last, but not least, it is not always possible to match the RMs with the samples that are being analysed, in composition and elemental concentrations. The production of RMs in Brazil is still incipient, with few exceptions, such as the important contribution of the IPT (Instituto de Pesquisas Tecnológicas) in São Paulo, in the area of production of RMs for industries (metal alloys and non ferrous materials). Other initiatives to be pointed out are the production of uranium and thorium RMs by CNEN (Comissão Nacional de Energia Nuclear) and RMs of chemical and biological substances, fungi, bacteriae, antivenom serum and vaccines, by the INCQS(Instituto Nacional de Controle de Qualidade na Saúde). In view of the growing demand of RMs by national laboratories and to the difficulties in acquisition of these materials from institutions like NIST(USA), IAEA (Austria) and IRMM (Belgium), it was decided, in the present project to develop all the steps for the production and characterization of a mussel (Perna perna) RM, which is an inedit initiative in Brazil. This marine organism was chosen due to its abundance in the Brazilian coast and to the fact that it is cultivated in the cities of Caraguatatuba, São Sebastião and Ubatuba, in São Paulo. There are several marine RMs that are produced by the cited institutions, such as the IAEA-407(Fish Tissue),NIST 2976(Mussel Tissue)and NIST 1566b(Oyster Tissue).These materials are very much utilized by analytical laboratories which develop research about environmental contamination of marine environments and specially in the LAN(Neutron Activation Analysis Laboratory)/IPEN,which is developing a study about biomonitoring of regions of the São Paulo coast, with support of the CNPQ,by using transplant experiments of the mussel Perna perna, in collaboration with the Oceanographic Institute of the University of São Paulo. For the characterization of the RM prepared at LAN/IPEN, two main analytical methods will be used: neutron activation analysis, NAA and atomic absorption (CVAAS and graphite furnace. NAA is a method traditionally used at LAN and used for many years for analysis of many elements, like;As, Ca, Cu, Co, Cr, Fe, Na, Sc, Se, Zn, REE elements. By AAS, Hg, Cd and Pb, not favourable for NAA, can also be determined. (AU)