Accuracy collaborative testing

The last step in establishing a standard method is to validate its transferability to other laboratories. An important step in the process of validating a method is collaborative testing, in which a common set of samples is analyzed by different laboratories. In a well-designed collaborative test, it is possible to establish limits for the method s precision and accuracy. 

This set of articles presents the computational details and actual values for each of the statistical methods shown for collaborative tests. These methods include the use of precision and estimated accuracy comparisons, ANOVA tests, Student s t-testing, The Rank Test for Method Comparison, and the Efficient Comparison of Methods tests. From using these statistical tests the following conclusions can be derived ... 

Other classes of reference materials now in existence include secondary reference materials. These are materials produced commercially for reference purposes, but whose guarantee rests soley with the producer. "Analyzed" materials such as geological materials obtained from the United Staes Geological Survey, represent test samples that complement the variety available from the previously mentioned sources. However, the "accepted" analyses reported for these materials are based upon consensus values obtained from large scale interlaboratory collaborative tests (round robins). Analysis of these materials can provide a useful means of comparing performance with other laboratories, but it does not ensure accuracy. In addi-... 

Collaborative Testing. A second approach to assessing accuracy, when no certified reference material is available, may be used in conjunction with analysis by independent methods and in-house materials. Sample exhanges with other laboratories can help establish the existence or absence of systematic errors in a method. Collaborative tests are most useful in this regard when some of the participating laboratories use different sample preparation and quantification. The utility of independent analysis methods and comparisons between destructive and non-destructive analysis is again emphasized here. 

The resulting metal, in the salt state, is dissolved in nitric acid and diluted to a known volume with double distilled water. The solution is analyzed by Atomic Absorption for the metals of interest. Metals such as Cadmium, Berylium and Nickel have very low threshold limit values which are set by OSHA and are frequently present in the sample in very low quantities. Many Atomic Absorption units are equipped with a hollow graphite tube atomizer which increases the sensitivity dramatically making it easier for the analyst to obtain reliable results for species present in the sample in very low concentrations. The validity of the metal fume data depends on sampling train calibration and the precision and accuracy of the analytical procedure. NIOSH has reported a 2% relative standard deviation in the analytical method which has been collaboratively tested. 

Results from recent proficiency tests on Sn in vegetable test materials have shown an unexpectedly large variation. This is likely to be a general problem with the determination of Sn in foodstuffs. An additional problem is that the available methods which are collaboratively tested and approved may not meet current requirements for accuracy. Thus, there is presently an uncertainty as to which method to choose for the determination of Sn in foods. 

The accuracy of any method depends to a large degree upon the skills and experience of those who not only collect the samples but also those who analyze the samples. Even for methods that are collaboratively tested, some laboratories are closer to the true values than others. Some laboratories may meet the precision and accuracy requirements of the method others may consistently far exceed them for the same method. 

Collaborative The principal purpose of collaborative testing is to assess the accuracy of... 

Sections on matrix algebra, analytic geometry, experimental design, instrument and system calibration, noise, derivatives and their use in data analysis, linearity and nonlinearity are described. Collaborative laboratory studies, using ANOVA, testing for systematic error, ranking tests for collaborative studies, and efficient comparison of two analytical methods are included. Discussion on topics such as the limitations in analytical accuracy and brief introductions to the statistics of spectral searches and the chemometrics of imaging spectroscopy are included. 

The reliability of a method can be determined by assessing certain method performance criteria including, specificity, accuracy, precision, limit of detection and quantitation, sensitivity, applicability, and practicability as appropriate (13). This very often requires that an extensive collaborative study be undertaken to obtain the necessary data. Methods that have successfully undergone this performance review testing have been considered to be validated for the purpose of the analysis (14). 

The ideal validated method would be the one that has progressed fully through a collaborative study in accordance with international protocols for the design, conduct, and interpretation of method performance studies. A typical study of a determinative method conducted in accordance with the internationally harmonized International Organization for Standardization (ISO)/International Union for Pure and Applied Chemistry (IUPAC)/AOAC International (AOAC) protocol would require a minimum of up to five test materials including blind replicates or split-level samples to assess within-laboratory repeatability parameters, and eight participating laboratories (15). Included with the intended use should be recommended performance criteria for accuracy, precision and recovery. 

Accuracy The closeness of agreement between a test result and the accepted reference value. Interlaboratory comparison (ILC) The organization, performance, and evaluation of tests on the same sample by two or more laboratories in accordance with predetermined conditions to determine testing performance. According to purpose, they can be classified as collaborative studies or proficiency studies. 

The collaborative study should be conducted in the environment of the intended use of the test by people with the same level of training as the anticipated users. This kind of a collaborative study is designed to test performance, including the environment, training, and the quality control system. The test may fare better in a laboratory-based collaborative study, where defects could be dissected out and corrected. The test developer may choose to test the system in a mini-collaborative study based in laboratories, but before final consideration, FSIS would like to see the results of the collaborative study conducted on-site. These circumstances are likely to produce estimates of the test accuracy, precision, and bias that will be seen in the field. 

Reference 9 describes a collaborate survey of over 28 laboratories testing the new Tentative Standard Method for Chlorinated Hydrocarbon Pesticides in distilled water. This method calls for two successive extractions utilizing a hexane, semi-automatic extraction as described by Kawa-hara et al, 10) and modified by Schaefer et al, (11) Three different chlorinated hydrocarbon pesticide mixtures were tested only three of eighteen pesticides analyzed showed a total error of less than 50%. This calculation of the total error was based upon Table 100 (3) which described the accuracy and precision of the new method (9). 

Interlaboratory survey, collaborative interlaboratory survey, quality control survey, multicenter evaluation a system for evaluating the accuracy and precision of reference methods conducted by individual clinical chemical laboratories, and for assessing the performance of analytical instruments Samples of the same specimen are analysed by different laboratories, and the range of interlaboratory scatter is determined for the particular analytical technique. In some countries, it is now mandatory for clinical chemical laboratories to participate is such quality assurance surveys, and those failing to fulfil requirements for a particular analyte may not be recognized by medical insurance companies. Similar surveys are conducted to test the reliability, accuracy, precision, running costs and ease of operation of new instru-... 

This is based on the principle of extracting the alcohol with an immiscible solvent and reading the per cent alcohol from the position of the meniscus. They used 70 ml. of pentasol (synthetic amyl alcohol), 28 ml. of toluene, and 1.8 ml. of 10% hydrochloric acid in a specially calibrated tube. The determination requires about 5 minutes, and an accuracy of 0.6% from 5% to 22% alcohol is claimed. Wines which tend to emulsify should be pretreated with charcoal. Etienne (1952) has reported on a collaborative study of about 100 determinations with his tube. In 43% of the cases the values fell within 0.15% of those determined by the pycnometer, 60% of the values were within 0.3, and 94% fell within 0.5. To reduce error he found that the temperature should be controlled at 25.5° C. (78° F.) in any case, the test should be conducted between 21.1° and 29.4° C. (70° and 85° F.)... 

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