Internal method

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. 

The most useful methods for quality assessment are those that are coordinated by the laboratory and that provide the analyst with immediate feedback about the system s state of statistical control. Internal methods of quality assessment included in this section are the analysis of duplicate samples, the analysis of blanks, the analysis of standard samples, and spike recoveries. 

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 framework development, the skeleton of the common behavior is one of two things either (1) an internal method specified on an interface that must be implemented by a specialized class, or (2) a template method in the superclass with the variant bits and pieces deferred to the subclasses. We will illustrate the latter design here. 

Regardless of the methods used to create the descriptors and construct the equation for the models, there is a need to validate the model by comparing the predicted bioactivities with the Experimental Bioactivities. Using the data that created the model (an internal method) or using a separate data set (an external method) can help validate the QSAR model. To determine if the model can be... 

CAB International. Methods in Agricultural Chemical Analysis a Practical Handbook (N.T. Faithfull)... 

The British equivalent to ISO 2781 is BS 903 Part Al2 which is identical to the international method. Rather surprisingly, ASTM does not appear to have a specific method for density at the present time. There is, however, a section on density in the standard on chemical analysis of rubber products, D2973, which briefly gives methods by pycnometer, hydrostatic weighing and a compressed volume densimeter. The weighing method does not mention the use of a sinker for densities less than 1. There is also a method for density of rubber chemicals, D1817)4, which uses the pycnometer method and, interestingly, specifies a vacuum pump to remove air before the measurement.. 

There is an international method, ISO 295113, for the determination of insulation resistance of rubbers. The test pieces specified are either flat sheets or tube or rod and the electrodes either conductive paint or metal bars. It is apparent by the reference to rigid materials that the wording has been lifted from a general document for insulating materials, presumably IEC 16714. There is no mention of metal backing plates for the paint electrodes and, to obtain consistent results with rubbers, the electrode system would need to be defined more precisely. 

The British equivalent BS 903-C515 covers plastics as well as rubbers and includes methods using taper pins, which are not applicable to rubber. It is in fact a copy of IEC 167, the general international method. Hence, there is a slightly curious situation of the BS following the IEC rather than the particular ISO method for rubbers. The essential question is whether the particular needs of rubbers merits a special adaptation of the test procedure. The UK did not think so and the ISO method only paid lip service to the particular needs of rubber. ASTM does not have a method specific to rubbers and the procedures are covered in D2574 for insulation materials generally. 

On anti-static and conducting products, it is usual to measure the resistance between specified points. More or less efficient electrode systems are used, contact resistance included and the resistance usually measured with a commercial insulation tester. The relevant international method is ISO 287820. This used to be used in conjunction with two specifications (ISO 2882 and 2883) for antistatic and conductive products and, consequently, had procedures detailing the electrodes to be used for the products in those standards. ISO 2882 and 2883 were withdrawn, largely because of no... 

The Gehman test is also standardised in BS903 Part A1318 and ASTM D105319. The British Standard is identical to the international method but the ASTM has a rather different layout as it covers coated fabrics as well as rubbers and a single point procedure is added for routine inspection. It only specifies a step temperature change procedure. 

It would appear that the common standard low temperature tests are not thought totally suitable for measuring effects of crystallisation because a hardness tests has been standardised for this purpose, even although hardness tests are not so commonly used for measuring the immediate effect of low temperature. The international method ISO 338733 and the British method BS 903 Part A6334 are the same and are applicable to unvulcanised as well as vulcanised rubber. This is probably one reason why the hardness test has been introduced because the other methods would not be satisfactory... 

ISO 4637 was developed from the British standard, BS 903 Part All51, which was eventually revised to be identical with the international method. It is one of those regrettable lapses in standardisation that this revision had to... 

W. C. Shermer, Union Camp Corp. internal method, unpublished. 

There are currently a number of recommended methods of analysis for the determination of a-and 0-acids in hops by HPLC (e.g., Fig. 2). The methods recommended by the Institute of Brewing, the American Society of Brewing Chemists, and the European Brewery Convention are summarized in Table 1. The method recommended by the latter two is in fact the same and is thus considered to be an international method. There are some key differences worthy of note here. Both clearly rely on the use of phosphoric acid to suppress the ionization of the acidic compo-... 

The European Brewery Convention also recommends a method for the simultaneous analysis of a-, / -, and iso-a-acids in a single chromatographic run. The method is more complex than the international method, because of differences in the UV maxima and in the polarities of the an-... 

Official methods of analysis of AOAC International, Method 988.11, 16th ed., 1999, Chapter 9, p. 24. 

The day after production, more extensive tests can be carried out to confirm the quality of the batch. The tests must be carried out by approved local or international methods (e.g., ISO or ASTM). Final release of the prepolymer is based on these results and the data obtained during the production of the prepolymer. 

Most internal methods aim for gels or hard points in the 100 to 200 pm size range and are therefore comparable to the GKR method. 

WHO should adopt published CIPAC and AOAC International methods suitable for the support of specifications (see also recommendation 2 in section 8.3 of this report concerning the copyright of published methods). 

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