Working range of an analytical

The working range of an analytical method is the interval between the upper and lower concentrations of the analyte in the sample for which it has been demonstrated that the method has acceptable precision, accuracy and linearity. This interval is normally derived from linearity studies and depends on the intended application of the method. However, validating over a range wider than actually needed provides confidence that the routine standard levels are well removed from nonlinear response concentrations, and allows quantitation of crude samples in support of process development. The range is normally expressed in the same units as the test results obtained by the analytical method. 

The working range of an analytical method denotes the range between the lower and upper concentration, for which accurate determinations are feasible. 

A well-defined relationship between detector response and analyte concentration is crucial for quantitative analyses. In the past, the working range of an analysis was often defined by the linear portion of the response vs. concentration curve. Although a linear relationship is desirable, it is no longer a requirement since powerful curvefitting data analysis programs are readily available. The important criterion is that the response-concentration relationship is constant and reproducible. 

To demonstrate the validity of an analytical method, data regarding working range/ calibration, recovery, repeatability, specificity and LOQ have to be provided for each relevant sample matrix. Most often these data have to be collected from several studies, e.g., from several validation reports of the developer of the method, the independent laboratory validation or the confirmatory method trials. If the intended use of a pesticide is not restricted to one matrix type and if residues are transferred via feedstuffs to animals and finally to foodstuffs of animal origin, up to 30 sets of the quality parameters described above are necessary for each analyte of the residue definition. Table 2 can be used as a checklist to monitor the completeness of required data. 

In contrast to many other validation protocols, the description of the NMKL validation process starts with the protocol of planned validation. This protocol should include, e.g., the needs of the client, available equipment, the chemical form in which the analyte occurs (i.e., in pesticide analysis the residue definition), matrix types, the availability of reference materials and the working range. Consequently, an extra paragraph is dedicated to the requirements for the documentation of validation results, which refers to the rules in Section 5.4.4 of EN 45001 (amended by ISO 17025). 

The first area covers laboratory analysis. Analysts can express results from data in a number of ways...mean, standard deviation, and range. The analysts can separate the error involved in various phases of an analytical problem. They can work on a single detection technique, which is univariate, or they can utilize more than one measuring technique, which is... 

Several successful attempts were done to transfer classical CEIA to a microchip-based format. This kind of miniaturization is a trend that can overcome the limitations of CE in high-throughput systems. On-chip CE offers both parallel analysis of samples and short separation times. Koutny et al. showed the use of an immunoassay on-chip (32). In this competitive approach fluorescein-labeled cortisol was used to detect unlabeled cortisol spiked to serum (Fig. 8). The system showed good reproducibility and robustness even in this problematic kind of sample matrix. Using serum cortisol standards calibration and quantification is possible in a working range of clinical interest. This example demonstrated that microchip electrophoretic systems are analytical devices suitable for immunological assays that can compete with common techniques. 

When compared with optical spectrometric techniques of elemental analysis, the techniques based on mass spectrometry provide an increase in sensitivity and in analytical working range of some orders of magnitude. For instance, the detection limits with ICP-MS are three orders of magnitude better than ICP-optical emission spectrometry (ICP-OES). Figure 1.45 shows the maximum sensitivity obtained for the different elements, using an ICP-MS coupling with a quadrupole. 

Stripping methods arc important in irace work because ihc preconceniraiion step permits the determi nation of minute amounts of an analyte with reasonable accuracy. Thus, the analysis of solutions in the range of 1() to 10 M becomes feasible by methods that are both simple and rapid. 

In connection with the calibration function performance, several characteristics are combined, such as the sensitivity of an analytical method and its working range. 

The acctuacy of an analytical method, i.e., the agreement between the average of the results and a true value, can be estimated by using reference materials. In spite of the large range of materials currently available, it may be difficult to obtain adequate standards for work at trace levels. Use of an internal standard can improve accuracy. An accuracy of 1% can be expected. 

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