Reproducibility of an analytical method

As noted earlier, the x -test for goodness-of-fit gives a more balanced view of the concept of fit than does the pure least-squares model however, there is no direct comparison between x and the reproducibility of an analytical method. 

Reproducibility as defined by ICH [2,3] represents the precision obtained between laboratories (Table 5). The objective is to verify that the method will provide the same results in different laboratories. The reproducibility of an analytical method is determined by analyzing aliquots from homogeneous lots in... 

Figure 6.5. Experimental design for the assessment of the repeatability, intermediate precision and the reproducibility of an analytical method.

Reproducibility, as defined by ICH, represents the precision obtained between laboratories with the objective of verifying if the method will provide the same results in different laboratories. The reproducibility of an analytical method is determined by analyzing aliquots from homogeneous lots in different laboratories with different analysts, and by using operational and environmental conditions that may differ from, but are still within the specified, parameters of the method (interlaboratory tests). Various parameters affect reproducibility. These include differences in room environment (temperature and humidity), operators with different experience, equipment with different characteristics (e.g., delay volume of an HPLC system), variations in material and instrument conditions (e.g., in HPLC), mobile phases composition, pH, flow rate of mobile phase, columns from different suppliers or different batches, solvents, reagents, and other material with different quality. 

It is well understood that the majority of variation in metabonomic experiments comes from the biological rather than analytical variation [83], Nevertheless, it is critical that the reproducibility of an analytical method is acceptable and that... 

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 ... 

The precision of an analytical method is a measure of the variability of repetitive measurements. Contributions from numerous sources affect precision, but the major components are within-laboratory (repeatability) and between-laboratory (reproducibility) variations. Precision is expressed as the relative standard deviation (or CV)... 

According to USP 28 [1], validation of an analytical method is the process by which it is established, through the conduct of laboratory studies, that the performance characteristics of the method meet the requirements for the intended analytical applications. Therefore, validation is an important step in determining the reliability and reproducibility of the method because it is able to confirm that the intended method is suitable to be conducted on a particular system. 

The robustness of an analytical method can be defined as a measure of the capability of the method to remain unaffected by small, but deliberate, variations in method parameters. The parameter therefore provides an indication of the method reliability during normal usage. The ruggedness of a method is the degree of reproducibility of test results obtained by the analysis of the same samples under a variety of conditions, such as different laboratories, different analysts, different instruments, different lot of reagents, different days, etc. 

In the context of an analytical method to establish the accuracy, precision, reproducibility, response function and the specificity of the analytical method with reference to the biological matrix to be examined and the analyte to be quantified. 

The precision of a test method is the variability between test results obtained on the same material using a specific test method (ASTM, 2004 Patnaik, 2004). The precision of a test is usually unrelated to its accuracy. The results may be precise, but not necessarily accurate. In fact, the precision of an analytical method is the amount of scatter in the results obtained from multiple analyses of a homogeneous sample. To be meaningful, the precision study must be performed using the exact sample and standard preparation procedures that will be used in the final method. Precision is expressed as repeatability and reproducibility. 

The ruggedness of an analytical method can generally be described as the ability to reproduce an analytical method in different laboratories or in different circumstances without the occurrence of unexpected differences in the obtained results. 

The precision of an analytical method is usually expressed as the standard deviation or relative standard deviation (coefficient of variation) of a series of measurements. Precision represents repeatability or reproducibility of the analytical method under normal operating conditions. Precision determinations permit an estimate of the reliability of single determinations and are commonly in the range of 0.3 to 3% for dosage form assays. 

The precision of an analytical method can be defined as the pattern of variation of single assays on a uniform sample. The precision serves to identify random errors and is described by the repeatability (variability within a laboratory) and reproducibility (variation between different laboratories). 

The ruggedness of an analytical method is determined by analysis of aliquots from homogeneous samples in different laboratories, by different analysts, using operational and environmental conditions that may differ but are still within the specihed parameters of the assay. The degree of reproducibility of test results is then determined as a function of the assay variables. This reproducibility may be compared to the precision of the assay under normal conditions to obtain a measure of the ruggedness of the analytical method. 

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. 

The robustness of an analytical method can be described as the ability to reproduce the method in different laboratories or under different circumstances without the occurrence of unexpected differences in the obtained results. The term ruggedness is considered here as a synonym for robustness. The robustness of a method is tested in a robustness test. The most frequently u.sed definition for robustness in this area is due to the International Conference on Harmonisation of Technical Requirements for the Registration of Pharmaceuticals for Human Use (ICH) [79,80. It defines robustness as follows. The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage."... 

The precision of an analytical method is the closeness of a series of individual measurements of an analyte when the analytical procedure is applied repeatedly to multiple aliquots of a single homogeneous volume of biological matrix [16], The precision is calculated as coefficient of variation (C.V.), i.e., relative standard deviation (RSD). The measured RSD can be subdivided into three categories repeatability (intra-day precision), intermediate precision (inter-day precision) and reproducibility (between laboratories precision) [16, 78, 79, 81],... 

The selection of reference materials is therefore critical in validating the performance of an analytical method (see Chapter 1). CRMs should be used at least in the initial evaluation studies and in establishing the acceptability of calibrators used in routine service. The specific characteristics of calibrators should be documented, along with the number of different concentrations of calibrating solutions and the frequency of their use. These latter choices depend on the characteristics of tlie analytical method, particularly the stability, reproducibility, and linearity. 

When a suitable certified reference material (CRM) is available, it has to be used in the validation process of an analytical method (Quevauviller et al., 1998). However, a non-certified RM produced following rigorous technical requirements and fit-for-purpose homogeneity and stability characteristics, can be used for intermediate reproducibility evaluation as well as in the organization of PT schemes (Emons et al., 2004 De Guillebon et al., 2001). 

Long-term reproducibility is the prime quality of an analytical method used for the study of stability. Stability must be performed on the element or substance to be certified. Extrapolations on the stability of tracers are of little interest. If the uncertainty of the method for an analyte is poor, even for large sample intakes, the analyst must refer to the experience on similar materials with higher contents or to the general chemical properties of the substance or element. In any other situations certification may be impossible. Such difficulties are mainly encountered in organic or organo-metallic analysis. Experience has shown that some substances may be stable in a matrix but unstable in another even similar one [46-47]. All analytical methods suffer from long term reproducibility. In some cases analysts have developed tools and tricks to minimise this effect. 

Reproducibility The precision of an analytical method, usually expressed as the standard deviation of determinations performed in different laboratories (and therefore by different analysts using different equipment on different days). (Section 2.7)... 

The precision of an analytical method is obtained from multiple analyses of a homogeneous sample. You can determine overall precision of the method, including sample preparation. Such precision data are obtained by one laboratory on one day, using aliquots of the homogeneous sample that have been independently prepared. Such interlaboratory precision is called repeatability. Interlaboratory precision, if appropriate, is also determined as part of a measurement of reproducibility or robustness of the method (see below). 

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