Prescriptive Approach


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.  [c.712]

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.  [c.712]

A good example of a prescriptive approach to quality assessment is the protocol outlined in Figure 15.2, published by the Environmental Protection Agency (EPA) for laboratories involved in monitoring studies of water and wastewater. Independent samples A and B are collected simultaneously at the sample site. Sample A is split into two equal-volume samples, and labeled Ai and A2. Sample B is also split into two equal-volume samples, one of which, Bsf, is spiked with a known amount of analyte. A field blank. Dp, also is spiked with the same amount of analyte. All five samples (Ai, A2, B, Bsf, and Dp) are preserved if necessary and transported to the laboratory for analysis.  [c.712]

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.  [c.713]

The advantage to a prescriptive approach to quality assurance is that a single consistent set of guidelines is used by all laboratories to control the quality of analytical results. A significant disadvantage, however, is that the ability of a laboratory to produce quality results is not taken into account when determining the frequency of collecting and analyzing quality assessment data. Laboratories with a record of producing high-quality results are forced to spend more time and money on quality assessment than is perhaps necessary. At the same time, the frequency of quality assessment may be insufficient for laboratories with a history of producing results of poor quality.  [c.714]

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.  [c.712]

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.  [c.712]

A good example of a prescriptive approach to quality assessment is the protocol outlined in Figure 15.2, published by the Environmental Protection Agency (EPA) for laboratories involved in monitoring studies of water and wastewater. Independent samples A and B are collected simultaneously at the sample site. Sample A is split into two equal-volume samples, and labeled Ai and A2. Sample B is also split into two equal-volume samples, one of which, Bsf, is spiked with a known amount of analyte. A field blank. Dp, also is spiked with the same amount of analyte. All five samples (Ai, A2, B, Bsf, and Dp) are preserved if necessary and transported to the laboratory for analysis.  [c.712]

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.  [c.713]

The advantage to a prescriptive approach to quality assurance is that a single consistent set of guidelines is used by all laboratories to control the quality of analytical results. A significant disadvantage, however, is that the ability of a laboratory to produce quality results is not taken into account when determining the frequency of collecting and analyzing quality assessment data. Laboratories with a record of producing high-quality results are forced to spend more time and money on quality assessment than is perhaps necessary. At the same time, the frequency of quality assessment may be insufficient for laboratories with a history of producing results of poor quality.  [c.714]

Historically the legal framework in the North Sea has been prescriptive in nature, that is specifying through statute precisely what should be undertaken and when. Following Piper Alpha, a comprehensive review of all aspects of health and safety in the North Sea was undertaken by Lord Cullen and his team. The resulting Cullen Report (ref 1) included consideration of the way in which other industries in the UK were regulated and in particular the goal setting philosophy advocated in the Robens Report (ref 2) which was published in 1974. In this Robens recognised that the best interests of health and safety require the commitment and involvement of two key parties - those who create the risks and those who are affected by them. The role of the government in this approach should be to set the minimum objectives and enforce them, not dictate the detail and prescribe the means to meet the set objectives. Robens stated in his report  [c.1010]

Once a control chart is in use, new quality assessment data should be added at a rate sufficient to ensure that the system remains in statistical control. As with prescriptive approaches to quality assurance, when a quality assessment sample is found to be out of statistical control, all samples analyzed since the last successful verification of statistical control must be reanalyzed. The advantage of a performance-based approach to quality assurance is that a laboratory may use its experience, guided by control charts, to determine the frequency for collecting quality assessment samples. When the system is stable, quality assessment samples can be acquired less frequently.  [c.721]

The problem in micronutrient fertilization is that of adequately identifying the need, reducing this to a prescription, compounding the fertilizer, and distributing it evenly in the soil. Prescription compounding is being used increasingly as deficiencies are better identified, but a shotgun approach is also used. In the shotgun method, a range of micronutrients is added to fertilizers at levels beUeved to be low enough to avoid harmful effects but adequate to prevent deficiencies. Fertilizers of this kind usually are produced in ammoniation—granulation plants. When these are sold as premium fertilizers because of the added micronutrients, the minimum guaranteed amounts of micronutrients allowed bylaw in most U.S. states are 0.02 wt % B, 0.05 wt % Cu, 0.10 wt % Fe, 0.05 wt % Mn, 0.0005 wt % Mo, and 0.05 wt % Zn.  [c.242]

Micronutrients in Granular Fertilizers. In the production of granular fertilizers, it is relatively simple and effective to incorporate micronutrient materials as feeds in the granulation process. A problem with this method, however, is that granulation processes are most efficient and economical when operated continuously to produce large tonnages of the same or similar composition. Frequent changes in product composition or storage of a wide range of grades is simply uneconomical. These factors seriously limit the practice of prescription micronutrient formulation in granular fertilizer production processes. Granulation processes more often use the shotgun approach. As a result, some unneeded elements are provided with no benefit.  [c.242]

Once a control chart is in use, new quality assessment data should be added at a rate sufficient to ensure that the system remains in statistical control. As with prescriptive approaches to quality assurance, when a quality assessment sample is found to be out of statistical control, all samples analyzed since the last successful verification of statistical control must be reanalyzed. The advantage of a performance-based approach to quality assurance is that a laboratory may use its experience, guided by control charts, to determine the frequency for collecting quality assessment samples. When the system is stable, quality assessment samples can be acquired less frequently.  [c.721]

An alternative approach, not unrelated to some of the geometric statistics methods, which is being pursued is the application of bond percolation concepts to fragmentation (Englman et al., 1984). This is also a probabilistic approach in which lattice bonds in a preassigned lattice are allowed to open through some random prescription until a certain level of fracture intensity is achieved. Fragment size distributions are assessed by determining the closed circuits obtained in the fractured lattice. In this approach, internal fracture damage not associated with fragment surfaces can occur. Statistical size distributions have been obtained by this method and compared with Mott s theoretical equation (Englman et al., 1984). Work in this area is continuing in attempting to demonstrate a relevance to fragmentation.  [c.311]

We can now take one of two approaches (1) construct a probabilistic CA along lines with the Metropolis Monte Carlo algorithm outlined above (see section 7.1.3.1), or (2) define a deterministic but reversible rule consistent with the microcanonical prescription. As we shall immediately see, however, neither approach yields the expected results.  [c.359]

A more accurate approach is to begin with a model of the charge distribution for each of the molecules. Various prescriptions for obtaining point charge models, such as fitting to the electrostatic potential of the molecule [135.136], are currently in use. Unfortunately, these point charge models are insufficiently accurate if only atom-centred charges are used [137]. Hence, additional charges are sometimes placed at off-atom sites. This increases the accuracy of the point charge model at the expense of arbitrariness in the choice of off-atom sites and an added computational burden. A less popular but sounder procedure is to use a distributed nuiltipole model [28, 138. 139] instead of a point charge model.  [c.209]

Urea concentration typically increases by about 50 to 100 mg/100 mL/24 h. Even a small residual clearance will prove numerically significant and, for oliguric patients, the slightly more complex formulas given in References 43 and 44 should be employed. The exponential decay constant in equation 12, Cl // V, is the net normalized quantity of hemodialysis therapy. It is calculated simply by multiplying the urea clearance in mL/min by the duration of hemodialysis, also in minutes, and dividing by the distribution volume in mL, which, in the absence of a better estimate, is taken as 0.58 x the patient weight. This parameter provides an index of the adequacy of hemodialysis (45) and based on retrospective analysis of various therapy formats, a value of 1.0 or greater for urea proposedly provides an adequate amount of hemodialysis for most patients. Although not without its critics, this approach has found nearly universal clinical acceptance, and represents the current prescriptive norm to hemodialysis therapy.  [c.37]

The holistic thermodynamic approach based on material (charge, concentration and electron) balances is a firm and valuable tool for a choice of the best a priori conditions of chemical analyses performed in electrolytic systems. Such an approach has been already presented in a series of papers issued in recent years, see [1-4] and references cited therein. In this communication, the approach will be exemplified with electrolytic systems, with special emphasis put on the complex systems where all particular types (acid-base, redox, complexation and precipitation) of chemical equilibria occur in parallel and/or sequentially. All attainable physicochemical knowledge can be involved in calculations and none simplifying assumptions are needed. All analytical prescriptions can be followed. The approach enables all possible (from thermodynamic viewpoint) reactions to be included and all effects resulting from activation barrier(s) and incomplete set of equilibrium data presumed can be tested. The problems involved are presented on some examples of analytical systems considered lately, concerning potentiometric titrations in complex titrand + titrant systems. All calculations were done with use of iterative computer programs MATLAB and DELPHI.  [c.28]

This expression has a formal character and has to be complemented with a prescription for its evaluation. A priori, we can vary the values of the fields independently at each point in space and then we deal with uncountably many degrees of freedom in the system, in contrast with the usual statistical thermodynamics as seen above. Another difference with the standard statistical mechanics is that the effective Hamiltonian has to be created from the basic phenomena that we want to investigate. However, a description in terms of fields seems quite natural since the average of fields gives us the actual distributions of particles at the interface, which are precisely the quantities that we want to calculate. In a field-theoretical approach we are closer to the problem under consideration than in the standard approach and then we may expect that a simple Hamiltonian is sufficient to retain the main features of the charged interface. A priori, we have no insurance that it  [c.806]


See pages that mention the term Prescriptive Approach : [c.712]    [c.712]    [c.228]    [c.359]    [c.360]   
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Modern analytical chemistry  -> Prescriptive Approach

Modern Analytical Chemistry  -> Prescriptive Approach