Quality assessment generally

The goals of this chapter do not include a "state of the art" literature review which would be appropriate for a more in-depth discussion of one particular problem area. Rather the intent is to illustrate mechanistic approaches to river quality assessment using the three globally relevant water quality problem areas discussed in the previous chapter dissolved oxygen depletion, erosion/deposition, and potentially toxic trace elements. The information provided does not include all rationale, methology or approaches used in the study as this is beyond the scope of the chapter. Additional general information on application of the intensive river quality assessment approach in the Willamette River basin may be found elsewhere (4-9, 11-14, 17). 

Quality control describes the measures used to ensure the quality of individual results or a batch of results. The measures used will vary according to the particular application. It is a means of evaluating the current performance of the method being used and the general procedures used in the laboratory. There are two types of quality control, namely internal quality control and external quality assessment. These are covered in detail in Chapters 6 and 7, respectively. 

There are some guidelines on the requirements for proficiency testing schemes. The most important is the new ISO/IEC 17043 Conformity assessment - General requirements for proficiency testing . It describes the development and operation of a PT scheme with all quality management requirements related to that. The first version of the International Harmonized Protocol for the Proficiency Testing of (Chemical) Analytical Laboratories was a result of a joint workshop of lUPAC, ISO and AOAC and was published in 1993. A 2nd, revised version was published in 2006. This protocol also sets out the requirements for the provider and for the PT scheme itself. 

Sample quality is generally assessed by the determination of /J-galactosidase activity. For MPS type IVB, the a-mannosidase activity is chosen as an indicator enzyme. Leukocyte homogenates that are sufficient for at least 20 separate runs are prepared from one source and aliquots are kept frozen. These samples serve as quality controls for each run. Heat-inactivated leukocyte homogenates may serve as a positive control (patient-mimics). 

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