Every day thousands of laboratories around the world perform microbiological tests on many different matrices such as water, food or biological material. The main purpose of these labs is to produce fast and results with quality. However, incorrect results may have important public health implications as well as strong economic impact.
For these reasons, the implementation of programs of quality control is not only necessary, but mandatory. These quality systems are based mostly on international standards, in order to demonstrate the technical competence of the laboratory and the reliability of the results they generate. In this sense, all the requirements for implementing a system of quality control are included in ISO 17025. This rule is intended to improve substantially the laboratory's management and ensure the validity of the results produced, demonstrating that the laboratory is technically competent and that it is producing accurate and credible results. This standard provides procedures for the implementation of external and internal quality control for all activities conducted in the laboratory verification of the quality of results and periodic verification of the quality control system.
One of the most important tools for quality control is the use of reference materials.
A reference material, according to the definition given in ISO GUIDE 30, is a substance or material in which one or more of its properties has a value sufficiently homogenous and well established to be used for the calibration of an apparatus, or the evaluation of a measurement, or to validate analytical methods.
The properties that a certified reference material should satisfy are as follows:
It is an indispensable requisite which means that the CRM must give the same certified property value within the same unit and between all the units of the CRM. From a practical point of view, it only needs to be sufficiently homogenous with respect to the property of interest, even though it is not so homogenous with respect to other properties.
It should be stable under conditions of transport, and the time limit of stability from reception until the container is opened should be known. The stability should refer to both, the certified properties and to the matrix.
It should be traceable to national or international reference standards, and this should be displayed in the certificate which the production organisation issues.
Concentration and known uncertainty
The certified values of the property of interest should be accompanied by the margins of error.
Similarity with real samples
They should be as similar as possible to the real life samples which will later be analysed by the analytical method used by the buyer, both in the composition of the matrix, and in the property value to be determined.