Assurance, quality

Quality assurance (QA) as defined by GLP is a team of persons charged with assuring the management that GLP compliance has been attained within the laboratory. They are organized independently of the operational and study program and function as witnesses to the entire research process. 

Quality assurance is a plaimed and systematic pattern of all actions necessary to provide confidence that adequate technical requirements are established, that products and services conform to established technical requirements, and that satisfactory performance is achieved. This means that quality assurance is proving that what we do is fit for purpose. 

There are a number of reasons for introducing quality assurance into a forensic science laboratory. One would be to ensure that we avoid issues in relation to the product (evidence) that we are analysing that might result in inappropriate analysis and destruction of the item or evidence. Another reason for quality assurance is to ensure customer (police and judicial systems) trust, and the last would be to avoid miscarriages of justice (i.e., that guilty individuals do not walk free and innocent individuals are not given a prison sentence). 

A quality assurance (QA) programme shall be established and documented for the radioactive waste incineration system to ensure that the applicable requirements are followed during the design, construction and citation stages of the facility. Further guidance may be found in Ref. [10] and the related Safety Guides. 

A quality assurance programme that describes the overall arrangements for the management, performance and assessment of the plant design shall be prepared and implemented. This programme shall be supported by more detailed plans for each stmcture, system and component so that the quality of the design is ensured at all times. 

Design, including subsequent changes or safety improvements, shall be carried out in accordance with established procedures that call on appropriate engineering codes and standards, and shall incorporate apphcable requirements and design bases. Design interfaces shall be identified and controlled. 

The requirements for quality assurance are considered in the light of properties only being defined as components are manufactured. Checks on incoming materials, process control, destructive and non-destructive evaluation are discussed and for each stage the use of data is considered. 

Fibre-reinforced plastics form a class of materials whose properties are only attained as the component is moulded. Any strategy for quality assurance must therefore take this primary factor into account. 

The ISO 9000/9003 set of standards provides a framework for managing quality control systems and is widely used throughout the world. Some of the key requirements are listed in Table 12.1. 

These aspects are considered in turn and related where possible to data presented in previous chapters. 

In accordance with the Code [13], the quality assurance programme should provide for the systematic assessment of its effectiveness. A specific assessment should be considered if modifications important to safety are introduced, new regulatory requirements become applicable or incidents or accidents occur. 

49 The operating organization should prepare for potential emergencies on the site. The operating organization should provide off-site officials with the information 

Requirements and guidance concerning preparedness for emergencies at nuclear power plants are given in Refs [14-17]. 

If a laboratory is unable to do accurate parasitology because of either the types of procedures offered or the quality of personnel available, it should arrange to have specimens appropriately prepared and submitted to a reference laboratory. 

Until about 1660 A.D. all knowledge of the form, structure and life processes of plants and animals was narrowly restricted to what could be seen with the naked (or very feebly assisted) human eye. Microorganisms were merely fabulous monsters. Visual limitations 

Unaided human vision fails to see objects less than about 100 p, (0.004 or 1/254 inch) in diameter or to perceive as separate objects 

TABLE 2.1 SOME LINEAR MEASURES COMMONLY USED IN MICROBIOLOGY 

In spite of the fact that his microscopes were not compound he obtained remarkable results with them. 

Engineering of process plant projects increasingly involves the application of a disciplined management system to ensure that the quality of product or service is built-in at every stage. In this context, quality is defined as fitness for purpose — that is, the product must be fit for the purpose for which it is designed. 

It is important to establish at the outset of a project whether Quality Assurance is to be applied. Quality Assurance requirements are directly applicable to four key areas  

Piiase A — Prepare plant/equipmenl for precornmissioning/mechanicat testing 

Phase B — Prepare services clean and pressure test systems Phase C — Check and prepare major mechanical equipment, insiruineniation, and protection systems Phase D — Final preparations for start-up 

Phase B — Charge with feedstock and so on. Start up plant and operate Phase F — Performance test and plant acceptance Phase G — Remainder of maintenance period 

The establishment, management, performance and evaluation of a quality assurance programme for a research reactor and its associated experiments are 

Management shall provide and demonstrate support for the effective implementation of the quality assurance programme in all work areas. The management aspects of the quality assurance programme shall include  

At all stages in the lifetime of the research reactor, work shall be planned and performed in accordance with established codes, standards, specifications, procedures and administrative controls. Items and services important to safety shall be specified and controlled to ensure their proper use, maintenance and 

It shall be ensured that items and services under procurement meet established requirements and perform as specified. Suppliers shall be evaluated and selected on the basis of specified criteria. Requirements for reporting deviations from procurement specifications shall be specified in the procurement documents. Evidence that purchased items and services meet procurement specifications shall be made available for verification before the items are used or the services are provided. 

The management at all levels shall periodically assess the processes for which it is responsible to determine its effectiveness in achieving the objectives for nuclear safety. Weaknesses in processes shall be identified and corrected. 

The focus of this chapter is on the two principal components of a quality assurance program quality control and quality assessment. In addition, considerable attention is given to the use of control charts for routinely monitoring the quality of analytical data. 

The steps taken during an analysis to ensure that the analysis is under control and that it is properly monitored. 

Those steps taken to ensure that an analysis is under statistical control. 

Those general laboratory procedures that, when followed, help ensure the quality of analytical work. 

Those instructions outlining how to properly use equipment and instrumentation to ensure the quality of measurements. 

The accuracy of an analysis can be determined by several procedures. One common method is to analyze a known sample, such as a standard solution or a quality control check standard solution that may be available commercially, or a laboratory-prepared standard solution made from a neat compound, and to compare the test results with the true values (values expected theoretically). Such samples must be subjected to all analytical steps, including sample extraction, digestion, or concentration, similar to regular samples. Alternatively, accuracy may be estimated from the recovery of a known standard solution spiked or added into the sample in which a known amount of the same substance that is to be tested is added to an aliquot of the sample, usually as a solution, prior to the analysis. The concentration of the analyte in the spiked solution of the sample is then measured. The percent spike recovery is then calculated. A correction for the bias in the analytical procedure can then be made, based on the percent spike recovery. However, in most routine analysis such bias correction is not required. Percent spike recovery may then be calculated as follows  

The percent spike recovery to measure the accuracy of analysis may also be determined by the EPA method often used in environmental analysis  

Quality assurance is an umbrella term that is applied correctly to everything that the laboratory does to assure product reliability. As the product of a laboratory is information, anything that is done to improve the reliability of the information generated falls under quality assurance. 

Quality assurance includes all the quality controls, the generation of expectations (acceptance limits) from the quality controls, plus a great number of other activities, such as (1) analyst training and certification (2) data review and evaluation (3) preparation of final reports of analysis (4) information given to clients about tests that are needed to fulfill regulatory requirements (5) use of the 

The operating organization should prepare and implement a comprehensive quality assurance programme covering all activities which may have an influence on the safe operation of the nuclear power plant. The programme should meet the requirements of the Code on Quality Assurance for Safety in Nuclear Power Plants and Qther Nuclear Installations [8] and should be made available to the regulatory body. 

The design of an interim spent fuel storage facility shall be subject to a quality assurance (QA) programme. This programme shall cover the activities, systems, comptments and materials specified in this guide. It shall be in accordance with the principles and objectives of the IAEA Code on the Safety of Nuclear Power Plants Quality Assurance [18] and related Safety Guides. 

The design specifications and analyses pertaining to safety related materials and systems of a spent fuel storage facility shall be documented. The documentation shall be maintained in accordance with the established QA programme. 

The design of an interim spent fuel storage facility shall provide for an appropriate programme of inspection and maintenance of safety related components and systems. The design of a spent fuel storage facility shall provide safe access to all systems, areas and components requiring periodic inspection and/or maintenance. The access provided shall be sufficient for the safe operation of all required tools and equipment and for the installation of spares. 

Provision should be made in the design for maintenance of hot cell components. This maintenance work can be done either in the cell or externally, and the design should take account of the preferred option. 

Particular attention needs to be paid to establishing an effective system of quality assurance for adhesive connections. Non-destructive test methods based on ultrasound, X-rays or the measurement of electrical or thermal conductivity are available but only of limited value in practice. Specific data on adhesion cannot always be obtained by these methods. This section examines the issue of quality assurance from a practical point of view. Many years of experience have shown that only a quality assurance system that takes into account the specific features of adhesive bonding technology can produce consistently satisfactory results over an extended production period. The information outlined here should be viewed as a general checklist to be adapted to the specific requirements of each manufacturing environment. 

An effective quality assurance system for elastic adhesives depends on continuous monitoring and checking of all quality-related parameters. If these are maintained within the prescribed limits, then the quality of the adhesive connection is guaranteed with little or no need to supplement these control measures with time-consuming and costly destructive testing. The overall cost of quality assurance can therefore be kept down to a commercially acceptable level. 

Selected to suit the production cycle and the service stresses to which the finished assembly will be subjected Consistency of composition and surface condition Selected to suit the production cycle and the service stresses to which the finished assembly will be subjected Working within the specified time limits (open time), taking account of temperature and relative humidity levels 

Adhesive-friendly joint design, dimensioning of joints to suit functional requirements of finished assembly External (e.g. IFAM Bremen) or internal courses organised in conjuction with adhesive suppliers 

Project study Construction of prototype End of test phase Series production 

Matters are further complicated by the fact, that some requirements come into conflict with each other. Therefore, it is often necessary to make compromises, when defining the quality of a molded article in terms of an optimum combination of specific features. 

Other requirements are directed more toward the injection molding process and the organization of the injection molding plant than toward the product per se. Examples include  

The profitability and competitiveness of plastics processing companies are determined by the increasing demands on their flexibility and on the quality of their products. 

If we consider the injection molding plants which supply the automotive and electrical industries, for example, we see that the increased quality demands result fi om the continuous development of new areas of application and from the growing proportions of technical injection-moldings. 

The increasing variety of products, a related increase in the number of products to be manufactured in smaller lots, and the intensified tendency toward automated manufacturing further increase the demands upon the manufacturing process and the assurance of the required product quality. Minimum stock-keeping by the automobile manufacturers also puts greater strain on injection molders, most of whom work under contract Under the just-in-time specifications, this particularly apphes to logistics and the meeting of deadlines. 

All testing and control steps are integrated into the manufacturing process. The elements of the quality assurance system are designed according to ISO 9001. Thus, it is ensured that the manufactured products comply with specifications. This is demonstrated by a process such as the one specially used for 8-m class mirror substrates. Correspondingly, the process is less complicated for large-scale Zerodur products than for blocks and bars with smaller dimensions. 

The analyses of raw materials and the performance of test melts are aimed at  

During the melting process, regular tests are performed on cast samples. Glass samples are examined regarding  

Furthermore, specimens are subjected to temper programs for fast ce-ramization, in order to gain insight into the properties of the subsequent glass ceramic during the process  

The frequency of the test is determined by the course of the process. Possible corrective measures modify the glass batch and the process control during melting. For large pieces Zerodur is melted discontinuously. If the above-mentioned tests reveal that the necessary glass quality has been attained, casting approval is given. For smaller dimensions (bars, blocks), on the other hand, Zerodur is melted continuously. 

Due to overregulation and contradictory effects such as unacceptable results from accredited laboratories, quality assurance in analytical chemistry is constantly under discussion and exposed to criticism. Certainly quality assurance (QA) will not improve analytical work and its quality, which is at present very high in routine analysis as well as in research and development. Documenting all important processes, however, will make results trackable and possibilities for improvements (errors, quality, costs etc.) will be made visible. Therewith QA leads to better transparency and thus improves comparability. Proving properties of the applied analytical procedure like bias, uncertainty, reproducibility etc., which is often viewed as a key objective of QA, is actually the bread-and-butter work in analytical chemistry and should be self-evident for every reliable analyst. 

In environmental analysis, clinical chemistry and pharmaceutical measurements, for example, QA is mandatory, because of obvious safety reasons and corresponding regulations. Also in analytical chemistry QA is becoming increasingly obligatory due to specific regulations but also due to customer requirements, e.g. government contracts. 

In analytical chemistry QA often is used for and understood as good quality analytical work , which means to check all analytical parameters and keep them under control. A good example for this is the use of QA samples in ICP-MS analysis applying external calibration. These QA samples are regularly measured materials, similar in composition to the samples routinely analysed, except that the analyte content is known, and so serve as proof of the absence of drift effects. Should the bias between measured and known anal)fte content exceed a certain level, the calibration has to be repeated. The control of the calibration s validity however should be checked regularly even if no QA system is installed. 

Being a topic by itself, QA is well summarised in reference 112. The definition as well as a description of QA is given in the literature, and some applications are presented in a number of articles.Applications of QA in the environmental field in particular are covered in detail in Chapter 9 of this book. 

International Standards Organization (1993) International Vocabulary of Basic and Genial Terms in Metrology (BIPM, lEC, IFCC, ISO, lUPAC, lUPAP, OIML) 2nd edn ISO, Geneva, ISBN 92-67-01075-1. 

The quality assmance programme description [14, 15] shoidd be prepared and implemented by the licensee and shoidd be available for regidatory review (and possibly approval) before the project begins. A software quality assurance plan should 

Identification of the hardware and software items to which the quality assurance prograrmne description applies and of the governing standards, procedirres and tools to be used on the project. 

For each document to be produced, indication in the quahty assmance programme description of who should review it and approve it for official release. A description of the project s organizational stmcture which should include assurance of the independence of quality assurance auditors. 

A description of the competence and training needs for persormel involved in the project. 

A mechanism for identifying, reporting and correcting non-conformance to standards and procedures. 

To attain the required quality standards, it is important to ensure that the I C systems important to safety are designed, manufactured, qualified, inspected, installed, operated, tested and maintained in accordance with a quality assurance programme that is prepared by the designer, manufacturer or installer and approved by the appropriate authority. This programme should be in accordance with the relevant Code and Safety Guides (Ref. [3], Safety Guides Q3 and QIO). 

The quality assurance programme should include all the activities necessary (1) to verify the adequacy of the design of the safety systems and (2) to ensure that the safety systems comply with all the applicable standards and requirements. 

COST Action B3 (1992-1997) was devoted to the development of new radiotracers for nuclear medicine application and methods of quality assurance. National institutions of sixteen European states participated in five Working Groups (WG). 

Working Group 1 was concerned with the standardization of methods for labeling and quality control  

The scientific goal of Working Group 1 (a) has been the development and updating of quality control methods to assure safety of Tc pharmaceuticals for parenteral application in nuclear medicine. Scientific institutions in 12 European countries have contributed their experience and results for comparison of the available methods. The Eu- 

Identity and purity, stability, and sterility and apyrogenicity. The identity and purity of radiopharmaceuticals is verified by determining the radionuclidic and radiochemical purity. Stability concerns the radioactive label, which is related to radiochemical purity at a certain time after preparation. Since Tc pharmaceuticals are formulated as sterile, pyrogen-free solutions, the safety requirements of drugs for parenteral use do apply. Safe handling of the radionuclide is equally important and must comply with Euratom Directives, regulated by national law for radiation protection, which also concerns the application of radionuclides in adults and in children for diagnostic procedures. 

An inherent difference between radiopharmaceuticals and nonradioactive medicinal products is their radioactive decay. In fact, Tc pharmaceuticals have an expiration of hours. After expiration, the radiopharmaceutical should no longer be used because its quality has changed. Radioactive decay puts stringent requirements on the production 

Where competent authority approval is required, such approval shall take into account and be contingent upon the adequacy of the quality assurance programme. 

The relevant competent authority shall arrange for periodic assessments of the radiation doses to persons due to the transport of radioactive material, to ensure that the system of protection and safety complies with the Basic Safety Standards [2]. 

What are the benefits of applying a quality management system (QMS) as opposed to a traditional more informal approach simply relying on normal supervision The application of an effective QMS, by its definition of procedures, its recording of inspection and test results, and its mechanisms for detecting and correcting anomalies, apart from its direct benefits, will give the necessary assurance that quality  

all actions organized in a structured, systematic manner with this objective in mind can be described as quality assurance (QA). 

Effective QA enables the EPCM contractor to master quality issues, getting it right first time with the resulting economies of time, money and effort. Externally, QA exercised by the EPCM contractor helps give confidence to the owner in the capacity of the former to deliver the plant to specified requirements. The same reasoning can be applied concerning suppliers and construction contractors. Their own QA measures produce internal benefits and, in addition, contribute to convincing the EPCM contractor and the owner as to their capabilities and the conformity of materiel supplied and works carried out. 

All personnel musthave adequate education, training, and experience. Resumes, job descriptions, and training records must be on file for all personnel sufficient staff must be available to conduct studies. Management must designate a study director, who establishes a quality assurance unit and is responsible for validating results. 

The study director, who must have appropriate training and experience, has overall responsibility for conduchon of study, assures that protocols are followed, and is solely responsible for authorizing changes in protocols. 

The quality assurance unit is mandatory and separate from study 

Facilities must be suitable for measurements and handling of test items administrative and personnel facilities must be adequate. 

A written protocol is required for each study that defines all aspects of how it is to be conducted and the records that are to be kept, the study must be conducted according to the protocol and monitored for conformance, and any changes must be explainable. 

This is a key issue in every aspect of the forensic examination of explosion scenes, and in subsequent analysis of evidential samples. Unless the results can withstand the meticulous scrutiny properly given to them in a court, they are useless. The requirements include  

Certainly, the following summary will mainly concern industrial production, however, it can also be a useful help for the nonindustrial user, according to the title of this book How to achieve flawless results . 

This list emphasizes the importance of the data generated by a radioanalytical chemistry laboratory. The results produced by radiochemistry procedures are often subject to intense scrutiny and even expression of skepticism by sample submitters. 

As these QA measures became more pervasive and intricate, their formal organization as a quality assurance plan (QAP) was deemed necessary. Every laboratory should prepare a QAP that meets all the requirements stated by its operating license, its nuclear materials license (see Section 13.8.2), and all local, state, and federal regulations. In addition, the laboratory must prepare a QAP suitable for each customer who may have different format preferences or requirements. 

The fraction of time devoted to QA measures is an important economic consideration that balances the situation with the funds dedicated to the program. 

Application of these measures to reduce the frequency of reanalysis required in the radioanalytical chemistry laboratory can be justified by a cost-benefit analysis. The general purpose of supporting acceptance of analytical results has a less determinate economic benefit. The time and effort devoted to QA has increased from about 10% of the total analytical workload to 25-30% at present, as regulatory agencies have required more quality control (QC) measurements and more supporting documents. This increasing cost includes QC measurements, organization and actions instituted to ensure correct and defensible data output. The costs and benefits of QA are considered in Section 11.4. 

Acronyms are used pervasively in this chapter. Although they may annoy the reader, these terms are in common parlance when discussing QA, both in the literature and during communication with certain regulatory agencies. 

A safe and highly available process plant implies a design of its components and equipment which meets the demands from the process (cf. [4, 5]). 

This requires a quality assurance concept which comprises all phases of the life cycle of the plant. 

The choice of appropriate structural materials, pre-tests of the materials, and suitable manufacturing methods are of special importance given the multitude of different substances in process plants. The safe containment of the substances must be ensured. 

In order to ensure compliance with the procedure a comprehensive surveillance is used. It comprises the 

All relevant personnel should be made aware of the importance to safety of the tasks that they perform for MS I and of the potential consequences for safety of technical, procedural or human errors. Experience of faults and hazards caused by errors in MS I procedures and practices at the nuclear power plant concerned or at other plants, and in other potentially hazardous industries, should be reviewed and incorporated into personnel training programmes as appropriate. 

The nature and extent of the QA programme should be consistent with the number of workers monitored, and the magnitude and likelihood of exposures expected in the workplaces to be covered by the monitoring programme. 

An analytical laboratory or direct measurement facility should have a designated QA representative. This representative should monitor QC procedures, perform internal audits of the programme, and be responsible for training all personnel in QA, both in general terms and in the speeific quality aspects of their individual work. 

Specific QC measnres for direct methods of assessing internal exposures are provided in Ref [7]. National regnlations may require that facilities coucemed with measurement and internal dose assessment be accredited. Such accreditatiou programmes will have specifications for QA and QC to be implemented. 

Adecpiate training of dosimetry service personnel is essential to ensure that they can perform their jobs reliably. Such training should include  

Ventilation, fume hoods and bench space are necessary for radiochemical operations. Shielded facihties should be provided for detectors, including those in direct assessment facilities. Access control to all facilities is necessary, both to protect sensitive equipment and to maintain appropriate confidentiality of records. The facility should have an appropriate continuous floor covering (e.g. viryl) to facilitate cleaning and decontamination. 

The operation of safety systems and safety related systems and components of spent fuel storage facilities shall be subject to QA requirements commensurate with their safety importance. 

In particular, for spent fuel storage facilities, QA shall be applied to all activities that concern  

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The DCPD method looks to be a niethod for ndt during production of P/M parts. In use in the P/M industry it may be an important tool in quality assurance. Work will continue towards implementation at a P/M plant. 

Cohen B., Improving Analog CT Image Quality , 1991, Research Thesis, Doctor of Science, The Department of Quality Assurance and Reliability,. Technion. 

A proposal of a system for quality assurance for industrial x-ray films 4.0 Common consideration... 

As the safety and quality of industrial components, equipments and constructions is correlated with the inspection sensitivity and this is influenced in radiography by the film system class, a continuous supervision of the film systems on the market seems to be urgently necessary. To support the confidence of the film users in the film properties specified by the film manufacturers such a system for quality assurance for industrial x-ray films is proposed by some manufacturers and BAM. This system will be open to all manufacturers, distributers and users of x-ray films. It will deal with all film systems inclusive those which are not specified by a manufacturer as for instance mixed systems. The system for quality assurance will be based... 

As a first step in the direction outlined here some manufacturers and BAM last year discussed the problems and the possible procedures of such a system of quality assurance. As a result of this meeting round robin tests for the harmonization of the measurements of film system parameters and a possible procedure of surveillance of the quality of film systems were proposed. Closely related to these the BAM offers to perform the classification of film systems. But as during the production of films variations of the properties of the different batches cannot be avoided, the results of measurements of films of a single batch will be restricted to this charge, while only the measurements and mean of several batches of a film type will give representative values of its properties. This fact is taken into account already in section 4 of the standard EN 584-1 which can be interpreted as a kind of continuous surveillance. In accordance with this standard a film system caimot be certified on the base of measurements of a single emulsion only. 

The detection sensitivity of radiography is related among others to the properties and quality of industrial x-ray film systems. Changes of the products, variations due to different emulsions and combinations of products of different manufacturers can influence the decisive properties of film systems as classified in EN 584-1.To ensure the quality of industrial x-ray film systems a system for quality assurance open to all interested parties is proposed which is based on periodical round robin tests and quality controls of the manufacturer or an independent third party institution. 

To operate the MPI or LPI equipment at stable and reprodncable inspection conditions modern units are equipped with a monitoring and control system called "Quality Assurance Package" (termed QAP). The QAP System is ba.sed on an industrial PC with a bus system and field sensors. It ensures that process parameters important for the reproducability of the MPI or LPI are controlled an held between defined limits by a central computer system. It can be adapted to any old system, as well as integrated into new systems. 

Any quality or performance deviations of the equipment are printed out, the system allows fully automated operator free inspection and quality assurance documentation. 

That set of modules includes alongside the traditional procedures related to product control, quality assurance procedures for conformity assessment. The intervention of a third party in these procedures comprises an initial audit of the manufacturer s quality system which must include both the specific technological aspects of the products concerned and the methodology of the quality assurance procedures. Furthermore the manufacturers are subject to periodic audits to ensure that the systems are maintained. Finally, on the occasion of unexpected visits, the notified body can carry out tests on the products. 

The use of these techniques is an important element of industrial policy since they contribute to the creation of a business friendly regulatory environment allowing the combination of measures taken for internal organisational reasons and obligations of certification without lowering the level of safety to be achieved. Wlienever possible a choice between product control and quality assurance procedures is offered to manufacturers. 

The second approach - creation of systems for non-destructive testing quality assurance in compliance with ISO standards 9000 series - considers the quality system as an assembly of organisational strueture, procedures, processes and resources necessary for overall quality management at the laboratory. This approach requires methodieal development. 

A comprehensive approach to the quality assurance in NDT would combine both approaches. It creates and maintains conditions for the people protection, safe operation of objects and products and preservation of the environment. 

ISO 9000-1 Quality management and quality assurance standards - Part 1 Guidelines for selection and use ... 

The "feedback loop in the analytical approach is maintained by a quality assurance program (Figure 15.1), whose objective is to control systematic and random sources of error.The underlying assumption of a quality assurance program is that results obtained when an analytical system is in statistical control are free of bias and are characterized by well-defined confidence intervals. When used properly, a quality assurance program identifies the practices necessary to bring a system into statistical control, allows us to determine if the system remains in statistical control, and suggests a course of corrective action when the system has fallen out of statistical control. 

The written directives of a quality control program are a necessary, but not a sufficient, condition for obtaining and maintaining an analysis in a state of statistical control. Although quality control directives explain how an analysis should be properly conducted, they do not indicate whether the system is under statistical control. This is the role of quality assessment, which is the second component of a quality assurance program. 

Internal methods of quality assessment should always be viewed with some level of skepticism because of the potential for bias in their execution and interpretation. For this reason, external methods of quality assessment also play an important role in quality assurance programs. One external method of quality assessment is the certification of a laboratory by a sponsoring agency. Certification is based on the successful analysis of a set of proficiency standards prepared by the sponsoring agency. For example, laboratories involved in environmental analyses may be required to analyze standard samples prepared by the Environmental Protection... 

In the previous section we described several internal methods of quality assessment that provide quantitative estimates of the systematic and random errors present in an analytical system. Now we turn our attention to how this numerical information is incorporated into the written directives of a complete quality assurance program. Two approaches to developing quality assurance programs have been described a prescriptive approach, in which an exact method of quality assessment is prescribed and a performance-based approach, in which any form of quality assessment is acceptable, provided that an acceptable level of statistical control can be demonstrated. 

With a prescriptive approach to quality assessment, duplicate samples, blanks, standards, and spike recoveries are measured following a specific protocol. The result for each analysis is then compared with a single predetermined limit. If this limit is exceeded, an appropriate corrective action is taken. Prescriptive approaches to quality assurance are common for programs and laboratories subject to federal regulation. For example, the Food and Drug Administration (FDA) specifies quality assurance practices that must be followed by laboratories analyzing products regulated by the FDA. 

Example of a prescriptive approach to quality assurance. Adapted from Environmental Monitoring and Support Laboratory, U.S. Environmental Protection Agency, "Handbook for Analytical Quality Control in Water and Wastewater Laboratories," March 1979. 

In a performance-based approach to quality assurance, a laboratory is free to use its experience to determine the best way to gather and monitor quality assessment data. The quality assessment methods remain the same (duplicate samples, blanks, standards, and spike recoveries) since they provide the necessary information about precision and bias. What the laboratory can control, however, is the frequency with which quality assessment samples are analyzed, and the conditions indicating when an analytical system is no longer in a state of statistical control. Furthermore, a performance-based approach to quality assessment allows a laboratory to determine if an analytical system is in danger of drifting out of statistical control. Corrective measures are then taken before further problems develop. 

Control charts were originally developed in the 1920s as a quality assurance tool for the control of manufactured products.Two types of control charts are commonly used in quality assurance a property control chart in which results for single measurements, or the means for several replicate measurements, are plotted sequentially and a precision control chart in which ranges or standard deviations are plotted sequentially. In either case, the control chart consists of a line representing the mean value for the measured property or the precision, and two or more boundary lines whose positions are determined by the precision of the measurement process. The position of the data points about the boundary lines determines whether the system is in statistical control. 

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