Analytical methods, comparison

Regression analysis is commonly applied in comparing the results of analytical method comparisons. Typically an experiment is carried out in which a series of paired values is collected when comparing a new method with an established method. This series of paired observations (xl,-, x2,) is then used to establish the nature and strength of the rela-... 

Setting Objective (as stated by authors) Analytic method Comparison group Input costs Outcomes included Results measured Comments... 

The viscosity calculated by the confined shear simulation is 1.11 Pa s at lOSO C. This agrees very well with the value measured previously for this composition within the (NNL). It also seems to have accounted for the mixed alkali effect, which could not be modeled using the simpler analytical methods. Comparisons at other temperatures and with other silicate, borosilicate, and aluminosilicate melts showed similar agreement. 

Procedures for determining the quaUty of formaldehyde solutions ate outlined by ASTM (120). Analytical methods relevant to Table 5 foUow formaldehyde by the sodium sulfite method (D2194) methanol by specific gravity (D2380) acidity as formic acid by titration with sodium hydroxide (D2379) iron by colorimetry (D2087) and color (APHA) by comparison to platinum—cobalt color standards (D1209). 

To the analytical chemist, a standard deviation31 is a logical figure of merit for the comparison of detectors. We shall merely introduce the important subject of counting errors (10.2) here. For present purposes, it suffices to know that these errors are predictable, and that they set a lower limit to the standard deviation in an analytical method that depends upon measuring the intensity of an x-ray beam by an integrating detector. 

Use of thermal stability tests (DTA s) to determine the heat sensitivity of a given process mixture is desirable. Recent advances in analytical methods permit good calorimetric determination of heat of reaction. Heat of reaction data are critical for exothermic reactor vent sizing. Heat impact from fire is usually small in comparison, but should not be neglected. 

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. 

Accuracy is the term used to describe the degree of deviation (bias) between the (often unknown) true value and what is found by means of a given analytical method. Accuracy cannot be determined by statistical means the test protocol must be devised to include the necessary comparisons (blanks, other methods). 

Hewitt AD, Miyares PH, Leggett DC, et al. 1992. Comparison of analytical methods for determination of volatile organic compounds in soils. Environmental Science and Technology 26 1932-1938. 

PRIOR R L and CAO G (1999) "In vivo total antioxidant capacity Comparison of different analytical methods, Free Rad Biol Med, 27, 1173-81. 

A comparison is made of the detector signal in the absorption versus scattering mode. Particle sizes are calculated for the standard latex samples and their mixtures using recently reported analytical. methods which account for imperfect resolution. 

How critically interdependent matrix and analytical methods can be is illustrated in the example of the analysis of a soil sample. Table 7.1 shows the method dependent certified values for some common trace elements. The soil had been subjected to a multi-national, multi-laboratory comparison on a number of occasions (Houba et al. 1995) which provided extensive data. The data was subjected to a rigorous statistical program, developed for the USEPA by Kadafar (1982). This process allowed the calculation of certified values for a wide range of inorganic analytes. Uniquely, for the soil there are certified values for four very different sample preparation methods, as follows ... 

Third, in order to ensure that a collaborated method is being performed properly, and that resultant data obtained is sound, an appropriate set of controls or reference materials is needed to test the method as it is being used (Chase and Long 1997). However, there is a difference in how one views the aforementioned concepts. For example, analytical method development is a process-oriented approach in which each step of the process is continually tested whereas, the use of a RM, standard control or comparison with another method is a result-oriented view (Taimer et al. 1995). 

Comparison of methods for calculating detection and quantification limits for analytical methods used for food... 

Until 1991, manufacturers seeking authorizations for pesticides had to fulfil country-specific requirements of validation of enforcement methods. The term enforcement method means analytical methods which are developed for post-registration control and monitoring purposes. The harmonization of these requirements was initiated with the European Economic Community (EEC) Council Directive 91/414/EEC and temporarily finalized with the Guidance Document on Residue Analytical Methods SANCO/825/00 rev. 6, dated 20 June 2000 [Santd et Protection des Consommateurs (SANCO)]. The evaluation of validation studies by the competent authority is conducted by comparison of these European Union (EU) requirements with the study results and most often without any practical experience of the method. Some details of this evaluation are discussed below. 

Consistent with other analytical methods, immunoassays must be validated to ensure that assay results are accurate. Initial validation involves an evaluation of the sensitivity and specificity of the immunoassay, while later validation includes comparison with a reference method. Because a goal of immunoassays is to minimize sample preparation, validation also includes testing the effects of sample matrices and(or) sample cleanup methods on results. The final steps in validation involve testing a limited number of samples containing incurred residues to determine if the method provides reliable data. 

Table 2. Comparison of analytical methods for U-series nuclides... 

Applications Chromatography is a preferred technique for additive analysis as it allows both separation of additives in a mixture and subsequent quantitation. Despite the developments in GC, this technique cannot separate many polymer additives. Even with its lower efficiency in comparison to GC, HPLC is today one of the cornerstones in a polymer additive laboratory. Judging by the number of publications in recent years, HPLC is first among analytical methods for additives (confirmation/identification/quantification). Most additives may be analysed by HPLC if they can be dissolved in an HPLC solvent and absorb UV light. Typical polymer/additive analyses are carried out using LPE followed by HPLC with UV or RI detection [605-611]. Verification of the identity of an analyte is then based on a combination of retention time, UV and RI evidence. RPLC is used most frequently for polymer/additive analysis, but normal-phase and SEC are also used. Consequently, techniques for additive analysis by HPLC are legion. 

The underlying calibration procedure of a newly developed analytical method has to be examined by basic validation studies to determine the reliability of the method and its efficiency in comparison with traditional methods. In order to ensure long-term stability, it is necessary to perform revalidations, which can be combined with the use of quality control charts, over meaningful time periods. 

As explained earlier, however, the actual constitution of a surfactant rarely conforms to its nominal structure. Consequently the theoretical method of calculation is of limited utility, practical methods being more reliable. The HLB value may be determined directly by analysis or by comparison with a range of surfactants of known HLB values. An analytical method for the sorbitan monolaurate described above uses Equation 9.2 [37]. 

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