External quality assurance systems control

Method Evaluation, Quality Control, and External Quality Assurance Systems of Analytical Procedures... 

The importance of a careful evaluation of the performance characteristics of analytical procedures and adequate quality control against a laboratory s own requirements have been emphasized. However, it is extremely important to establish comparability between laboratories, i.e., the analytical result should be independent of the laboratory performing the analysis. An ongoing monitoring of the analytical performance against the norm of other laboratories is provided by external quality assurance systems. This external evaluation supplied by comparisons between analytical results of different laboratories estimates the between-laboratory differences. The main value of the external quality assurance systems is not only to highlight repeatability and reproducibility performance between laboratories but also to assess systematic errors. 

Statistical Analysis of Results and Performance Characteristics. A common problem with most external quality assurance systems has been the determination of the true value for a control sample. Because the true value is an ideal concept, the data are evaluated against the estimated true value, which may be established from (1) the amount of analyte spiked to the test samples (2) a group of reference laboratories using definitive or reference methods (3) the consensus mean, which is the mean of the results obtained by the participants after exclusion of outlier. It is the responsibility of the coordinators to ensure and demonstrate that the reference values are reliable [6]. 

For external quality control currently (inter)national intercomparison programs are running frequently, e.g., the British external quality assurance system (EQAS) for Cd-B. 

Sampling is just the beginning of the analytical process. On the way from sampling to the test report a lot of different requirements for high quality measurements have to be considered. There are external quality assurance requirements on the quality management system (e.g. accreditation, certification, GLP), internal quality assurance tools (e.g. method validation, the use of certified reference material, control charts) and external quality assurance measures (e.g. interlaboratoiy tests). 

In order to implement the quality policy in the daily work, quality management systems are installed, covering quality planning, quality control, quality assurance and quality improvement. To ensure that the quality assurance system is in place and effective, external standards are used, for example the DIN EN ISO 9000 ff. standard system, commonly shortened to ISO 9000 (DIN is an acronym for Deutsches InstitutfiXr Normung, meaning German Industry Standard ). 

There are two uses of chemical standards in chemical analysis. In the first place, they may be used to verify that an instrument works correctly on a day-to-day basis - this is sometimes called System Suitability checking. This type of test does not usually relate to specific samples and is therefore strictly quality assurance rather than quality control. Secondly, the chemical standards are used to calibrate the response of an instrument. The standard may be measured separately from the samples (external standardization) or as part of the samples (internal standardization). This was dealt with in Section 5.3.2. 

Nowadays, all analytical laboratories are aware of the cmdal importance of proper quality assurance activities. Although quality control directives explain how an analysis should be conducted, they do not indicate whether the system is under statistical control. Therefore, the written guidelines of a quality control program are a necessary, but not a sufficient, condition for obtaining and maintaining proper statistical control. This is the role of quality assessment, which includes internal methods coordinated within the laboratory and external methods organized and maintained by an outside agency. 

During the processing of the adhesive bonds or coatings, a detailed documentation of all production steps is essential to control and assure the quality. This can be directly integrated into a quality management system of the executing company and comprises standard forms that have to be filled out by the employee when the individual production step is completed. Thus, all different steps are reported and can be reproduced even after a certain period of time. Furthermore, an external quality control is usually established in case of security-relevant bonds. It is provided by official building authorities and ensures the consistent application as it was approved in advance. 

The goals of quality assessment are to determine when a system has reached a state of statistical control to detect when the system has moved out of statistical control and, if possible, to suggest why a loss of statistical control has occurred so that corrective actions can be taken. For convenience, the methods of quality assessment are divided into two categories internal methods that are coordinated within the laboratory and external methods for which an outside agency or individual is responsible. The incorporation of these methods into a quaKty assurance program is covered in Section 15C. 

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