Analytical method, single

Analytical method Single element Multiple elements Molecules Surface composition Crystal structure Other... 

An external standardization allows a related series of samples to be analyzed using a single calibration curve. This is an important advantage in laboratories where many samples are to be analyzed or when the need for a rapid throughput of samples is critical. Not surprisingly, many of the most commonly encountered quantitative analytical methods are based on an external standardization. 

The regression models considered earlier apply only to functions containing a single independent variable. Analytical methods, however, are frequently subject to determinate sources of error due to interferents that contribute to the measured signal. In the presence of a single interferent, equations 5.1 and 5.2 become... 

A variety of statistical methods may be used to compare three or more sets of data. The most commonly used method is an analysis of variance (ANOVA). In its simplest form, a one-way ANOVA allows the importance of a single variable, such as the identity of the analyst, to be determined. The importance of this variable is evaluated by comparing its variance with the variance explained by indeterminate sources of error inherent to the analytical method. 

An analysis of variance can be extended to systems involving more than a single variable. For example, a two-way ANOVA can be used in a collaborative study to determine the importance to an analytical method of both the analyst and the instrumentation used. The treatment of multivariable ANOVA is beyond the scope of this text, but is covered in several of the texts listed as suggested readings at the end of the chapter. 

Two samples taken from a single gross sample and used to evaluate an analytical method s precision. 

In preparing this textbook, I have tried to find a more appropriate balance between theory and practice, between classical and modern methods of analysis, between analyzing samples and collecting and preparing samples for analysis, and between analytical methods and data analysis. Clearly, the amount of material in this textbook exceeds what can be covered in a single semester it s my hope, however, that the diversity of topics will meet the needs of different instructors, while, perhaps, suggesting some new topics to cover. 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

Harrington, D. A. Ultrahigh-Vacuum Surface Analytical Methods in Electrochemical Studies of Single-Crystal Surfaces 28... 

In a production environment, the quality control department does not ordinarily concern itself with single applications of analytical methods, that... 

Soriaga, M. P., D. A. Harrington, J. L. Stickney, and A. Wiekowski, Ultrahigh-vacuum surface analytical methods in electrochemical studies of single-crystal surfaces, in Modem Aspects of Electrochemistry, J. O M. Bockris et al., Eds., Vol. 28, Kluwer, New York, 1996, p. 1. 

Guideline for Single-laboratory Vahdation of Analytical Methods for Trace-level Concentrations of Organic Chemicals, in Principles and Practices of Method Vahdation, ed. A. Flajgelj and A. Ambrus, MPG Books, Bodmin, pp. 179-252 (2000). 

Non-NADA methods may be designed to detect multiple residues and they may be designed for use in multiple species. In order to validate these multi-residue methods, modifications to the validation protocol relative to single analyte methods are made. Additional laboratories will participate in the method trial, but the number of samples... 

Even if most examples and procedures presented apply to in-house validation, the procedure does not distinguish between validations conducted in a single laboratory and those carried out within inter-laboratory method performance studies. A preference for inter-laboratory studies can be concluded from the statement that laboratories should always give priority to methods which have been tested in method performance studies. Within the procedure a profound overview of different categories of analytical methods according to the available documentation and previous external validation is given. For example, if a method is externally validated in a method performance study, it should be tested for trueness and precision only. On the other hand, a full validation is recommended for those methods which are published in the scientific literature without complete presentation of essential performance characteristics (Table 9). 

AOAC/FAO/IAEA/IUPAC Expert Consultation, Guidelines for Single Laboratory Validation of Analytical Methods for Trace-level Concentrations of Organic Chemicals, Workshop, 8-11 November 1999, Miskolc, Hungary (1999). Also available on the Word Wide Web http //www.iaea.oi trc/(see pesticides —> method validation). 

Methods submitted include single- and multi-analyte methods for parent compounds and for degradates of concern. Pesticide regulatory methods are needed for each type of environmental matrix fate methods may be designed for soil, water, plant tissue, animal tissue or air, but are predominantly for soil and water. Analytical methods need to include a complete description of the procedure, materials and equipment in order to be completely reproducible. The methods should be practical and rapid and, to the extent possible while maintaining other quality objectives, inexpensive (often State and local regulatory agencies with few available resources need to utilize them). 

As probabilistic exposure and risk assessment methods are developed and become more frequently used for environmental fate and effects assessment, OPP increasingly needs distributions of environmental fate values rather than single point estimates, and quantitation of error and uncertainty in measurements. Probabilistic models currently being developed by the OPP require distributions of environmental fate and effects parameters either by measurement, extrapolation or a combination of the two. The models predictions will allow regulators to base decisions on the likelihood and magnitude of exposure and effects for a range of conditions which vary both spatially and temporally, rather than in a specific environment under static conditions. This increased need for basic data on environmental fate may increase data collection and drive development of less costly and more precise analytical methods. 

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