Analytical performance parameters

Principles and Characteristics Whereas parameters most relevant to method development are considered to be accuracy, system precision, linearity, range, LOD, LOQ, sensitivity and robustness, method validation parameters are mainly bias, specificity, recovery (and stability of the analyte), repeatability, intermediate precision, reproducibility and ruggedness. However, method development and validation are highly related. Also, validation characteristics are not independent they influence each other. Acceptance criteria for validation parameters should be based on the specification limits of the test procedure. Quantitation and detection limits need a statement of the precision at their concentration levels. Procedures used for validation of qualitative methods are generally less involved than those for quantitative analytical methods. According to Riley [82], who has discussed the various parameters for validation of quantitative analytical methods, the primary statistical parameters that validate an analytical method are accuracy and precision. 

Accuracy is the measure of exactness of an analytical method, or the closeness of agreement between the measured value and the conventionally accepted true or reference value [94], The tme value can be obtained in several ways. Results of the method may be compared with those from an established reference method. Alternatively, accuracy can also be assessed by comparing with a sample of known concentrations, for example, a CRM. If no CRM is available, recourse can be taken to a blank sample matrix of interest spiked with a known concentration by weight or volume. The accuracy should be examined over a range that extends beyond the range of samples the method is likely to analyse. In practice, 10% deviations from certified values are commonly observed, cfr. the VDA-001 to 004 (Cd in PE) standards. For accuracy of HPLC methods, cfr. ref. [95]. 

The limits of quantitation (LOQ) are the lowest cq. highest concentrations of an analyte in a sample that can be determined with acceptable precision 

The range of an analytical method is the (inclusive) interval between the upper and lower levels of analyte that have been demonstrated to be determined with precision, accuracy, and linearity using the method. 

Ruggedness is the degree of reproducibility of results obtained by analysis under a variety of conditions, expressed as % relative standard deviation 

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Analytical procedures are classified as being compendial or non-compendial in character. Compendial methods are considered to be valid, but their suitability should be verified under actual conditions of use. To do so, one verifies several analytical performance parameters, such as the selectivity/specificity of the method, the stability of the sample solutions, and evaluations of intermediate precision. 

A number of experimental considerations must be addressed in order to use XRF as a quantitative tool, and these have been discussed at length [75,76]. The effects on the usual analytical performance parameters (accuracy, precision, linearity, limits of detection and quantitation, and ruggedness) associated with instrument are usually minimal. 

Baseline separation of the cephalosporin antibiotic cephradine, its main impurity cephalexin, and other related impurities was achieved by MEKC. The method was validated in compliance with the USP XXII analytical performance parameters and the results were comparable with a validated LC method, depicting CE to be a valuable alternative technique to LC in pharmaceutical quality control. In most cases, the amount of impurities relative to the main compound measured by MEKC is similar to that obtained by LC. However, some reports reveal that there are differences in number and amount of impurities between MEKC and LC analysis. MEKC permitted the determination of seven known and three unknown impurities in cefotaxime and the results were in good agreement with those of LC. ° MEKC yielded a higher amount of the cefotaxime dimer but a lower amount of an unidentified impurity with respect to LC. The differences may be due to the easier formation of the dimer in the aqueous sample solvent used in MEKC compared to the hydroorganic... 

Analytical performance parameter I Quantitative Limit tests III... 

Guidelines for the selection of analytical performance parameters required for method validation are given in Table 11. 

Data Elements Use this section to provide thorough and complete documentation of the validation of the analytical method. Include summaries of experimental data and calculations substantiating each of the applicable analytical performance parameters. These parameters are described in the following section. 

Analytical Performance Parameter Assay Category I Assay Category II Limit Quantitative Tests Assay Category III... 

NIR spectroscopy became much more useful when the principle of multiple-wavelength spectroscopy was combined with the deconvolution methods of factor and principal component analysis. In typical applications, partial least squares regression is used to model the relation between composition and the NIR spectra of an appropriately chosen series of calibration samples, and an optimal model is ultimately chosen by a procedure of cross-testing. The performance of the optimal model is then evaluated using the normal analytical performance parameters of accuracy, precision, and linearity. Since its inception, NIR spectroscopy has been viewed primarily as a technique of quantitative analysis and has found major use in the determination of water in many pharmaceutical materials. 

The United States Pharmacopoeia (U.S.P.) [5] in a chapter on validation of compendial methods, defines analytical performance parameters (accuracy, precision, specificity, limit of detection, limit of quantitation, linearity and range, ruggedness, and robustness) that are to be used for validating analytical methods. A proposed United States Pharmacopeia (U.S.P.) general chapter on near-infrared spectrophotometry [6] addresses the suitability of instrumentation for use in a particular method through a discussion of operational qualifications and performance verifications. 

The steps to be included into the analytical process Selection of analytical performance parameters Model solution (sample) to be used for validation experiments Degree of instrumentation Stability problems... 

The aim of the analysis should be kept in mind when analytical performance parameters are selected for the validation experiments. Table 5 lists the most important analytical performance parameters used for validation of TLC and HPLC methods. As is apparent from the data presented in Table 5, the parameters used for the two chromatographic techniques are not very different. The importance of each individual parameter used in the experiments to validate TLC or HPLC methods is, however, different, especially if the purpose of the analysis is considered. This is demonstrated in Table 5, where the primary analytical parameters are indicated as a function of the analytical aims. 

Table 5 Analytical Performance Parameters used for Validation of HPLC and of Nonin-strumentalized and Instrumentalized TLC Methods...

Unlike HPLC, TLC is an off-line technique sample application, chromatographic development, and detection are separated in time and space. The validation procedure itself and the significance of the various analytical performance parameters during validation research are different depending on the degree of instrumentation (see data in Table 5). 

Environmental conditions Experiments Analytical performance parameters Calculated data... 

The analytical performance parameters (precision, / /value, Rs, etc.) considered to be sensitive to changes in the experimental variables should be selected. 

Acceptable deviation(s) from the value of the prespecified analytical performance parameter(s) can be defined, including maximum and/or minimum value. 

Variation in chamber systems and in environmental coruiitions One of the most important aspects of ruggedness testing is to determine the effects of variations in chamber systems and environmental conditions on the analytical performance parameters. The quality of the chromatograms obtained is highly influenced by the running conditions (type, shape, and size of chambers, presaturation conditions, temperature, humidity, etc.). 

Plates from the same sources The same experiments are performed on three plates supplied by the same manufacturer. Analytical performance parameters Rf, R precision, lowest detectable quantity Sample Model A, and B or C. 

UM-chamber The same experiments are performed on plates with same particle size and dimension as in conventional chamber. Analytical performance parameters Rf, precision, lowest detectable quantity Sample Model A and B or C. Temperature 5°C Eluent 10% (rel) amount prior to run Forced flow chamber Instrumental conditions are changed. Analytical performance parameters R, Rf, precision, lowest detectable quantity Sample Model A and B or C. 

Drying 5°C temperature Running distance The same experiments are performed, but the running distance differs with 10% (rel). Analytical performance parameters precision... 

For not more than 2 variables, one or more analytical performance parameters fail to meet criteria. 

For more than two variables, one or more analytical performance parameters fail to meet criteria but the analytical performance parameters meet criteria within 75% of the prespecified deviation range (RDR is higher than 0.75). or... 

If one or more analytical performance parameters fail to meet criteria the simplest way of estimating the deviation range to be used in daily practice is to construct a response window for the limit values of a criterion in a given variable range, as illustrated in Figure 8. 

All validation data, including definitions, determinations, and calculations of the analytical performance parameters, together with densitograms (if available). 

The following analytical performance parameters were included into the validation process selectivity stability during chromatograidiic development and in solution spot stability prior to the run and after development linearity and range precision reproducibility limit of quantitation limit of detection accuracy. The definitions used for the performance parameters the methods applied to determine them and the acceptance criteria were also described. Therefore, these papers can be recommended to be used by practicising chromatographers. 

For validation it is not always necessary to evaluate each analytical performance parameter. 

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