Accuracy of an analytical method

The issue of data reproducibility had been the previous focus of the AOAC Official Methods Program. The TDRM will assist AOAC in responding to an expanded scope of it mission to include statements of accuracy with AOAC methods. This extra step requires independent verification of the accuracy of measurements generated by the method. Accuracy of an analytical method must be verified at three separate points ... 

It is generally difficult to identify developments with high potential where interferences do not preclude general application. To ensure the relevance of a method, its application to real sample analysis must be demonstrated. The accuracy of an analytical method should be confirmed by an independent method, or by the analysis of certified reference materials. Detailed comparative studies of the method developed with other well-established methods for polymer/additive analysis are not frequent in the analytical literature. Nevertheless, some examples may be found in Section 3.6. Improvements in analytical techniques are reasonably sought in sample preparation and in hyphenated chromatographic techniques. However, greatest efficiency is often gained from the use of databases rather than accelerated extraction or hyphenation. 

The accuracy of an analytical method is given by the extent by which the value obtained deviates from the true value. One estimation of the accuracy of a method entails analyzing a sample with known concentration and then comparing the results between the measured and the true value. The second approach is to compare test results obtained from the new method to the results obtained from an existing method known to be accurate. Other approaches are based on determinations of the per cent recovery of known analyte spiked into blank matrices or products (i.e., the standard addition method). For samples spiked into blank matrices, it is recommended to prepare the sample at five different concentration levels, ranging over 80-120%, or 75-125%, of the target concentration. These preparations used for accuracy studies usually called synthetic mixtures or laboratory-made preparations . 

The error of an analytical result is related to the (in)accuracy of an analytical method and consists of a systematic component and a random component [14]. Precision and bias studies form the basis for evaluation of the accuracy of an analytical method [18]. The accuracy of results only relates to the fitness for purpose of an analytical system assessed by method validation. Reliability of results however has to do with more than method validation alone. MU is more than just a singlefigure expression of accuracy. It covers all sources of errors which are relevant for all analyte concentration levels. MU is a key indicator of both fitness for purpose and reliability of results, binding together the ideas of fitness for purpose and quality control (QC) and thus covering the whole QA system [4,37]. 

Systematic Error and Random Error. An analytical result can be affected by a combination of two different kinds of experimental error systematic error and random error. Systematic errors are associated with the accuracy of an analytical method and are the difference of the mean value from the true value. The measure of this difference is the bias. The mean is only an estimate of the true value because only a limited number of experiments can be carried out. The estimate becomes better when more experiments have been carried out. In conclusion, since all the measurements are estimates, the true value can be approached only with replicate measurements. 

The accuracy of an analytical method is estimated as the percentage difference (bias) between the mean values generated by the method and the true or known concentrations. Accuracy is usually synonymous with systematic errors. Systematic errors cause all the results in a series of replicates to deviate from the true value of the measured quantity in a particular sense (i.e., all the results are too high or all are too low) (20). Accuracy has also been used in recent years to refer to any error causing a single measurement to deviate from the true value (i.e., to encompass elements of random and systematic errors) (21). 

The accuracy of an analytical method is the extent to which test results generated by the method and the true value agree. The true value for accuracy assessment can be obtained in several ways. 

A common situation is one in which we wish to test the accuracy of an analytical method by comparing the results obtained from it with the accepted or true value... 

ISO uses two terms, trueness and precision , to describe the accuracy of a measured value. Trueness refers to the closeness of agreement between the average value of a large number of test results and the true or accepted reference value. Precision refers to the closeness of agreement of test results, or in other words the variability between repeated tests. The standard deviation of the measured value obtained by repeated determinations under the same conditions is used as a measure of the precision of the measurement procedure. The repeatability limit r (an intra-laboratory parameter) and the reproducibility limit R (an inter-laboratory parameter) are calculated as measures of precision. Again, precision and trueness together describe the accuracy of an analytical method. 

Where do correct values come from for measuring accuracy of an analytical method Philosophically, no one really knows the absolutely true value of a measurement, but the best we can do is to measure the sample by a widely accepted procedure and to compare the experimental value to this. In many cases, the accepted method will be published by an association or society which is involved in setting procedures. Two such organizations are the Association of Official Analytical Chemists (AOAC) and the American Society for Testing and Materials (ASTM). Another approach is to obtain already analyzed and certified samples from an agency, for example, the National Institute of Standards and Technology (NIST). Your experimental answer can then be compared to the provided results to test its accuracy. 

Definition The accuracy of an analytical method is the closeness of test results obtained by that method to the true value. Accuracy may often be expressed as percent recovery by the assay of known, added amounts of analyte. 

Determination Determine the accuracy of an analytical method by applying that method to samples to which known amounts of analyte have been added both above and below the normal levels expected in the samples. Calculate the accuracy from the test results as the percentage of analyte recovered by the assay. 

The accuracy of an analytical method is the degree of closeness between the true value of analytes in the sample and the value determined by the method and is sometimes called trueness [78], Accuracy can be measured by analyzing samples with known concentrations and comparing the measured values with the true values. According to FDA [16] the accuracy for bioanalysis should be determined by a minimum of five determinations for at least... 

Definition The trueness or accuracy of an analytical method is given by the extent to which the value obtained deviates from the true value. It is often expressed as the amount determined by analysis expressed as a percentage of the known amoimt of active ingredient added to the matrix material. It is a measure of the exactitude of the method. 

The accuracy of an analytical method is defined as the inverse of the difference between an estimate and the true value that would be obtained by an ideal method. It is heavily dependent upon the specificity of the method. The precision is defined as a function of the agreement between repeated estimates carried out on fractions of the same sample, and is... 

The three methods recommended by lUPAC for assessment of the accuracy of an analytical method in a singlelaboratory validation are, in order of preference ... 

When a sample is repeatedly analyzed in the laboratory using the same analytical method, results collected will deviate from each other to some extent The deviations, representing a scatter of individual values around a mean value, are denoted as statistical or random errors, a measure of which is the precision. Deviations from the true content of a sample are caused by systematic errors. An analytical method only provides true values if it is free of systematic errors. Random errors make an analytical result less precise while systematic errors give incorrect values. Hence, the precision and accuracy of an analytical method have to be discussed separately. Statements regarding the accuracy are feasible only if the true value is known. 

The accuracy of an analytical method may be defined as the extent to which its results coincide with the truth. If the mean of a large number of measurements closely coincides with the truth, the method may be said to be accurate. Accuracy in this sense is really freedom from bias. Bias is primarily a characteristic of the procedure, although it may be influenced by the operator. 

The best way to assess the accuracy of an analytical method is to analyze certified reference material (CRM). CRM must be chosen from those matrices that are most similar... 

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