Rejectable quality level

When using the defect-detection approach to quality control certain problems develop. Inspection does nothing to improve the process and is not very good at sorting good-from-bad. Also, sampling plans developed to support an acceptable quality level (AQL) of 5%, for example, say that a company is content to deliver or reject 5% defects. 

Acceptance criteria means the product specifications and acceptance/rejection criteria, such as acceptable quality level and unacceptable quality level, with an associated sampling plan, that are necessary for making a decision to accept or reject a lot or batch (or any other convenient subgroups of manufactured units). 

The properties of such a decision rule need to be examined carefully from the perspective of both the sponsor/laboratory and client [28]. Indeed, the probability of accepting a run with respect to the quality level n of the assay depends on its performance criteria, bias and precision (<5M) and (erM), as seen in Equation 5.2. As performance of the assay deteriorates, a smaller proportion of results is expected to fall within the pre-specified acceptance limits. Then, from both the sponsor and regulatory perspectives, it would be better to have an acceptance criterion that is more likely to reject the runs when the expected proportion n of results within the acceptance limits... 

For example, a 95% probability that a batch is as good as the AQL does not exclude other probabilities that the batch is worse (for example the 10% probability level, sometimes called the lot tolerance per cent defective (LTPD) or unacceptable quality level, can be several percentage points worse than the AQL). It is the relationship of AQL to LTPD that more closely identifies the quality risk in any statistical sampling plan, and illustrates why the use of national plans as simple accept and reject figures fails to tap their full potential. 

Quality control refers to that part of good pharmaceutical manufacturing practices concerned with the operations of verification of quality levels acceptance or rejection of raw materials, acceptance or rejection of semifinished or finished products, estimation of the stability of products, examination of returned products and supervision of retained sample stores. 

Let s look at right quality the level the customer wants or better if possible. Most customers want zero defects. The traditional method was to use a random sample and develop an acceptable quality level (AQL). A sampling plan was developed and then the sampling standard tables were looked at to determine if the lot should be accepted or rejected. Using the acceptable quality level indicated that the customer was willing to accept some defects. In most cases today this method is not used. With the advent of Six Sigma the levels of acceptability have come way down, approaching zero defects. 

A sampling plan for attributes is a method to overcome this problem. An example of such a plan is the Accepted Quality Level system (AQL) (See Sect. 24.5.4. for a more complete description of AQL and Sect. 20.4.5 for a statistic background). In order for the AQL system to be successful an extensive and statistically planned random sample has to be selected. The defects that are found are classified into levels, for example critical, major, minor. Within each level the system defines an acceptable quality level . When a quality level is exceeded, then a batch should be rejected. This method of testing requires time and expertise. Sampling has to be performed from a large number of containers from the same batch. Within the pharmaceutical industry it is often necessary for such tests to be carried out by the container manufacturer. For smaller enterprises such as pharmacies quality control can be undertaken by the wholesaler or an independent laboratory. Within a (hospital) pharmacy the quality control is often limited to a visual comparison to reference samples and a check of the presence of the supplier s statement that the containers comply with the agreed specifications [46]. 

The AQL-system is a sampling and assessment system frequently used to check cOTitainers. It is a type of attribute assessment, see Sect. 20.4.5 for statistical background. AQL means Acceptable Quality Level. The AQL-value is the percentage of rejected units accepted by a supplier or buyer to approve the crmcemed batch. Tables are available which describe, for a certain batch size N and an agreed AQL-value, how large the test sample n should be and how many units of that sample are allowed to show a specific defect The AQL-system classifies defects in classes ... 

Production-line vibration checks are an effective method of ensuring product quality where machine tools are involved. Such checks can provide advanced warning that the surface finish on parts is nearing the rejection level. On continuous process lines such as paper machines. 

Color is often used as an indicator of food quality due to short evaluation times and cost savings. " People consider the colors of raw materials, half fabricates, and final products in order to make decisions to accept or reject food products. For example, levels of anthocyanins have been used to evaluate the adulteration of various pigmented food products, and fruit color is a strong determinant of ripeness. The role of the food handler in controlling the colors of food products is very important because such judgments are subjective. ... 

HPGPC also was used for quality control of incoming raw materials. Figure 8 shows the chromatograms of two different batches of blocked isocyanate crosslinkers. One was acceptable and the other was too reactive. As can be seen from the HPGPC traces, the level of the component eluted at retention volume 40 is much higher for CX-46 than for CX-48. This component was associated with free isocyanate functionality which in excess would make CX-46 too reactive. With this information, either the necessary adjustment for the presence of excessive free isocyanate functionality could be made or this particular batch from the supplier could be rejected. 

Although impurities generated in the coupling of N-Boc pyrrolidine and aryl bromide 3 were cleanly rejected during crystallization of 5 and, therefore, did not affect the quality of the product, we decided to isolate and identify these impurities for better understanding of the coupling reaction (Scheme 8.14). The debromi-nated compound 28 was observed at a very low level (<1%). The enamide impurity... 

Cement manufacturers use a number of quality control measures. Key among these is careful selection of fuels for recycling. Fuels that contain metals above specified levels, for instance, will be rejected. For that reason, each shipment of fuel is carefully analyzed to determine its ingredients. If the fuel fails to meet predetermined specifications, it will not be used. 

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