Accepted reference value

Alcohol sulfates commonly have free alcohol and electrolytes as impurities. Other hydrophobic impurities can also be present. A method suitable for the purification of surfactants has been proposed by Rosen [120]. Consequently, commercial products have CMCs that deviate from the accepted reference values. This was demonstrated by Vijayendran [121] who studied several commercial sodium lauryl sulfates of high purity. The CMC was determined both by the conductimetric method and by the surface tension method. The values found were similar for both methods but while three samples gave CMC values of 7.9, 7.8, and 7.4 mM, close to the standard range of 8.0-8.2 mM, three other samples gave values of 4.1, 3.1, and 1.7 mM. The sample with a CMC of 7.9 mM was found to have a CMC of 8.0 mM with no detectable surface tension minima after purification and recrystallization. This procedure failed in all other cases. 

The accuracy of an analytical procedure expresses the closeness of agreement between the value, which is accepted either as a conventional true value or an accepted reference value and the value found. This Is sometimes termed trueness . 

In analytical chemistry, the term error (used in the sense of deviation) is defined by the difference between the test result (xtest) and the true value (x, i.e., the accepted reference value, see ISO 3534-1 [1993] Fleming et al. [1997]). The term may be related both to measured value y and analytical value x which correspond to each other according to the sensitivity factor b of an analytical procedure. 

The difference between the expectation According to GAT VIII [1997] of the test results and an accepted reference value . 

Measurements are subject to systematic errors as well as the random errors covered in Section 4.3.2. Bias is the difference between the mean value of a large number of test results and an accepted reference value for the test material. The bias is a measure of trueness of the method. It can be expressed in a number of ways, i.e. simply as a difference or as a ratio of the observed value to the accepted value. This latter representation, when expressed as a percentage, is often termed recovery. This represents how much of the analyte of interest has been extracted from the matrix and measured. This is dealt with in Section 4.6.3. 

Accuracy is often used to describe the overall doubt about a measurement result. It is made up of contributions from both bias and precision. There are a number of definitions in the Standards dealing with quality of measurements [3-5]. They are only different in the detail. The definition of accuracy in ISO 5725-1 1994, is The closeness of agreement between a test result and the accepted reference value . This means it is only appropriate to use this term when discussing a single result. The term accuracy , when applied to a set of observed values, describes the consequence of a combination of random variations and a common systematic error or bias component. It is preferable to express the quality of a result as its uncertainty, which is an estimate of the range of values within which, with a specified degree of confidence, the true value is estimated to lie. For example, the concentration of cadmium in river water is quoted as 83.2 2.2 nmol l-1 this indicates the interval bracketing the best estimate of the true value. Measurement uncertainty is discussed in detail in Chapter 6. 

As mentioned in Section 4.3.3, bias is the difference between the mean value (x) of a number of test results and an accepted reference value (xo) for the test material. As with all aspects of measurement, there will be an uncertainty associated with any estimate of bias, which will depend on the uncertainty associated with the test results Uj and the uncertainty of the reference value urm> as illustrated in Figure 4.7. Increasing the number of measurements can reduce random effects... 

Accuracy The difference between a single test result and the accepted reference value. 

Specificity Ability to assess unequivocally the analyte in the presence of components that may be expected to be present Accuracy Expresses the closeness of agreement between the value that is acceptable, either as a conventional time value or an acceptable reference value, and the value found Precision Expresses the closeness of agreement between a series of measurements obtained from multiple sampling of the same homogeneous sample under the prescribed conditions Repeatability Expresses the precision under the same operating conditions over a short interval of time Limit of Detection Lowest amount of analyte that can be detected in a sample... 

Traeness is a property related to systematic errors. It is the closeness of agreement between the average value obtained from a large set of test results and an accepted reference value. It can be checked with reference materials or in interlaboratory comparisons. 

Method validation seeks to quantify the likely accuracy of results by assessing both systematic and random effects on results. The properly related to systematic errors is the trueness, i.e. the closeness of agreement between the average value obtained from a large set of test results and an accepted reference value. The properly related to random errors is precision, i.e. the closeness of agreement between independent test results obtained under stipulated conditions. Accnracy is therefore, normally studied as tmeness and precision. 

Closeness of agreement between test result and accepted reference value Closeness of agreement between independent test results obtained under stipulated conditions Precision under conditions where independent test results are obtained with same method on identical test items in same laboratory by same operator using same equipment within short intervals of time Precision under conditions where independent test results are obtained with same method on identical test items in same laboratory but by different analysts using different equipment over extended period of time Precision under conditions where test results are obtained with same method on identical test items in different laboratories with different operators using different equipment 1... 

Closeness of agreement between expectation of test result (expected mean value) and accepted reference value (true value)... 

An interlaboratory bias study is a limited form of method performance study used to determine the bias of a standard method or the bias introduced by laboratories that use the standard method. Laboratories are chosen for their competence in performing the method, and the organization is the same as for a method performance study. The number of laboratories in the study is determined by the statistics required. If the bias (6) is calculated as the difference between accepted reference value and mean of n laboratories results, the significance can be tested using the standard deviation of the mean, sR/ /n. The Student s t statistic is calculated as... 

The word accuracy is used to indicate the reliability of a measurement or an observation, but it is, more specifically, a measure of the closeness of agreement between an experimental result and the true value. Thus, the accuracy of a test method is the degree of agreement of individual test results with an accepted reference value. 

Bias difference between the population mean of the test results and an accepted reference value a systematic error as contrasted to random error, and there may be one or more systematic error components contributing to the bias (ASTM E-456). 

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. 

Accuracy means the closeness of agreement between a test result and the accepted reference value. It is determined by determining trueness and precision [57], In a strict sense, the accuracy of a method is affected by systematic (bias) as well as random (precision) error components, but the term is often used to describe only the systematic error component, i.e., in the sense of bias. In this sense sometimes... 

Accuracy / recovery The amount of material recovered from surface, swab or rinse solution compared to accepted reference value. A correction factor should be established in the analytical method to represent incomplete recovery + +... 

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. 

ISO tlie closeness of agreement between tlie test result and tlie accepted reference value. 

According to ISO, bias is the difference between the expectation of the test results and an accepted reference value [17]. It may consist of more than one systematic error component. Bias can be measured as a percent deviation from the accepted reference value. The term trueness expresses the deviation of the mean value of a large series of measurements from the accepted reference value. It can be expressed in terms of bias. 

The positive validation conclusion was based on the comparison of the results of the analysis of suitable reference materials obtained with the new program and with its precursor in the same conditions, and also on comparison of their deviations from the accepted reference values for these materials, with the corresponding uncertainties. 

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