Precision method validation elements

The interpretation and implementation of published methods invariably differ at different laboratories due to diversity of utilized instruments, their incidental elements and supplies, and the differences in method interpretation. Each analytical method must be validated at the laboratory before it is used for sample analysis in order to demonstrate the laboratory s ability to consistently produce data of known accuracy and precision. Method validation includes the construction of a calibration curve that meets the acceptance criteria the determination of the method s accuracy and precision and the MDL study. A method SOPs must be prepared and approved for use. Method validation documentation is kept on file and should be always available to the client upon request. 

Verification implies that the laboratory investigates trueness and precision in particular. Elements which should be included in a full validation of an analytical method are specificity, calibration curve, precision between laboratories and/or precision within laboratories, trueness, measuring range, LOD, LOQ, robustness and sensitivity. The numbers of analyses required by the NMKL standard and the criteria for the adoption of quantitative methods are summarized in Table 10. 

Precision and recovery data. Validation data can be gathered for toxin analogues calibrated by RRFs. " Blank seafood matrices can be fortified with aliquots of semi-purified extracts of contaminated shellfish or algae containing the toxins of interest. Comparison to an aliquot spiked into solvent enables calculation of recovery and replication enables determination of precision. Thus, several key elements of method validation can be accomplished without a CRM and only minimal revalidation is required when one comes available. 

Parallel method comparisons are used to establish the validity of a new method developed for five organic pharmaceutical compovmds, food colors, and color additives. The standard methods such as the Japanese Standard Food Additives and Japanese Standard of Cosmetic Ingredients method, based on volumetric and gravimetric titration, have been used to establish new methods developed for the determination of I, Cl, Br, and SO4 in food colors. The results obtained indicate good agreement in both accuracy and precision for procedures based on the oxygen flask method as compared with the standard methods. In addition to anion elemental analysis, method validation has also been carried out for metal analysis such as that of Ce(III), Th(IV), and U(VI), with the results showing acceptable limits of variation. 

The next section deals with method validation of quantitative TLC methods. Two questions should, however, be answered prior to discussing the validation experiments namely, whether the statistical evaluation of data elements, such as precision, accuracy, and reproducibility should be calculated on the basis of measured peak heights or peak areas, and whether the internal or external standard methods, or area normalization should be used to yield quantitative results for the assay. Without going into detail, the most important advantages and limitations of peak height and peak area measurements, and those of the different methods of quantification are summarized in Table 4. 

Internal standard (IS) calibration requires ratioing of an analytical signal to an IS which has very similar characteristics to that of the analyte of interest (an element which is similar to the analyte either in mass, ionisation potential or chemical behaviour). Quantitative analysis applying internal standardisation is the most popular calibration strategy in ICP-MS, as improvements in precision are obtained when the technique is appropriately used. Of course, the validity of this calibration method requires that one ensures a good selection of the correct internal standard. For this purpose it is possible to resort to chemometric methods [16]. 

Once a method is established, precision may be determined by suitable replicated experiments. However it is in inter-laboratory trails that the problems with environmental methods often show up. It is accepted that for trace analysis RSD values of tens of percent are likely. In studies conducted in Western Australia on pesticide residues in bovine fat RSD values for dieldrin were 12% and for dia-zonium were 28%. It is typical to see a quarter of the laboratories in such a trial producing values that could be termed outliers. In the previously mentioned study, 5 laboratories out of 26 had z> 3 for aldrin. In a parallel study RSD values for petroleum in dichloromethane and water were 40% and 25%, respectively. The conclusions of these studies was that there was poor comparability because of the different methods used, that accreditation apparently made no difference to the quality of results, and that a lack of understanding of definitions of the quantities to be analysed (for example gasoline range organics ) caused non-method errors. In relation to methods, this is contrary to the conclusion of van Nevel et al. who asserted that the results of the IMEP round of analyses of trace elements in natural and synthetic waters showed no dependence on method [11]. If properly validated methods do yield comparable results, then one conclusion from the range of studies around the world is that many environmental methods are not validated. It may be that validated methods are indeed used, but not for exactly the systems for which they were validated. 

Solid-liquid mixing processes can be simulated with good precision when sound CFD methods are used. The application of a combination of the virtual finite element method and the network-of-zone approach was used in this work to analyze the complex flow and suspension mechanisms in a coaxial mixer. Experiments carried on the laboratory scale confirmed fhe validity of the predictions. 

The analytical procedures to assess stability must encompass the elements common to validating analytical assays. The methods must be validated according to the parameters of accuracy, precision, robustness and specificity, limits of detection and quantitation, linearity of active ingredient assays, degradants, and other reaction products. More information on how to develop stability indicating methods is discussed in Chapter 7. Validation of these methods is discussed in Chapter 8. 

For validating analytical methods for testing stability samples, the following elements need to be considered accuracy, precision, linearity, range, specificity, robustness, and detection and quantitation limits. Each of these terms is defined and discussed below. 

A simple definition of accuracy is a measure of how close the experimental value is to the true value. If a pharmaceutical product containing 50 mg of API was analyzed, an accurate method would yield results which would average close to 50 mg. Validation of this element is typically combined with precision (see Section... 

Aggarwal et al. recently implemented methods for the determination of isotope ratios and concentrations of different elements in biological specimens. Thermally stable and volatile chelates were identified for a number of trace elements Ni [43], Cr [45], Pt [46], Cu [33], Se [47], Co [48], Cd [49], Pb [44], Hg [50], and Te [51]. Memory effect was evaluated and found to be insignificant. Precision and accuracy in the measurement of isotope ratios was evaluated. Finally, the isotope dilution GC-MS method was validated by analyzing NIST reference materials (e.g., urine, semm), by comparing the results with ETAAS and by using the standard addition approach. 

Gas-phase chemistry studies of atomic and molecular rare-earth and actinide ions have a deep-rooted history of more than three decades. In gas phase, physical and chemical properties of elementary and molecular species can be studied in absence of external perturbations. Due to the relative simplicity of gas-phase systems compared to condensed-phase systems, solutions or solids, it is possible to probe in detail the relationships between electronic structure, reactivity, and energetics. Most of this research involves the use of a variety of mass spectrometry techniques, which allows one exerting precise control over reactants and products. Many new rare earth and actinide molecular and cluster species have been identified that have expanded knowledge of the basic chemistry of these elements and provided clues for understanding condensed-phase processes. Key thermodynamic parameters have been obtained for numerous atomic and molecular ions. Such fundamental physicochemical studies have provided opportunities for the refinement and validation of computational methods as applied to the particularly challenging lanthanide and actinide elements. Among other applications, the roles of... 

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