Comparative method

Reaction of alkyl halides 1 with hexamethylenetetramine 2 (trivial name urotropine) followed by a hydrolysis step, leads to formation of primary amines 3 free of higher substituted amines. This method is called the Delepine reaction, a comparable method is the Gabriel synthesis. 

Because of the mild reaction conditions, and its broad applicability, the Knoevenagel reaction is an important method for the synthesis of a ,/3-unsaturated carboxylic acids. Comparable methods are the Reformatsky reaction, the Perkin reaction, as well as the Claisen ester condensation. The Knoevenagel reaction is of greater versatility however the Reformatsky reaction permits the preparation of a ,/3-unsaturated carboxylic acids that are branched in a-position. 

Clark, W. L., Cowan, R. L. and Walker, W. L., Comparative Methods for Measuring Degree of Sensitisation in Stainless Steel, ASTM STP 656, ASTM, Philadelphia, 99 (1978)... 

Procedures can also be used to analyze straight lines with respect to slope and position, compare sample values to standard population means, compare methods, and detect differences in small samples. 

The accuracy of a determination may be defined as the concordance between it and the true or most probable value. It follows, therefore, that systematic errors cause a constant error (either too high or too low) and thus affect the accuracy of a result. For analytical methods there are two possible ways of determining the accuracy the so-called absolute method and the comparative method. 

Comparative method. Sometimes, as in the analysis of a mineral, it may be impossible to prepare solid synthetic samples of the desired composition. It is then necessary to resort to standard samples of the material in question (mineral, ore, alloy, etc.) in which the content of the constituent sought has been determined by one or more supposedly accurate methods of analysis. This comparative method, involving secondary standards, is obviously not altogether satisfactory from the theoretical standpoint, but is nevertheless very useful in applied analysis. Standard samples can be obtained from various sources (see Section 4.5). 

Tetraethyllead fluid in four gasolines supplied by the Ethyl Corporation was determined by the comparative method on weighed samples, aluminum serving as standard. These tetraethyllead fluids could have contained dibromo- or dichloroethane, or both, in addition to the lead compound. 

As Table 3-2 shows, iu and iSt are so nearly identical in these measurements by the comparative method that values of kstmst and kumu for which they are identical can be calculated with high precision. For these values, Equation 3-15 becomes... 

The great advantage of the comparative method is that the interpretation of the results, being based upon Equation 3-16, does not directly involve the output currents. 

The comparative method is wholly reliable only if deviations from the relation... 

First, the conventional spectrograph is being converted into a sequential instrument that uses the comparative method (9.7). The conversion consists principally in equipping such a spectrograph (one x-ray beam, one crystal, one detector) with mechanisms that make possible the comparison of standard and unknown at preselected positions of 20. 

RATIO CORRECTED FOR BACKGROUND. COMPARATIVE METHOD. This... 

The reliability of the results depends in large measure on how well deviations from the (ideal) linear relationship between log / and dry weight per unit area can be eliminated or allowed for. As is well known, this can be accomplished by the comparative method (3.10), provided that standard (reference system) and unknown, identical in mass, shape, and elementary composition, are exposed to the same x-ray beam. In the cytological investigations, these conditions are difficult to meet, not only because the samples are complex in composition, but also because they are very small, as is clear from the units employed (micromicrograms per square micron or 10 12 gram per 10 8 sq cm). 

In the language of this book, the procedure summarized by Equation 11-2 may be described as follows (1) The analysis is made by the comparative method, unknown and standard being compared as in Section 7.8. (2) By the use of intensity ratios, the comparison is... 

Since there are no comparable methods for determining the preferred conformation of 24 when it reacts with the enzyme, researchers in the field are... 

As XRF is not an absolute but a comparative method, sensitivity factors are needed, which differ for each spectrometer geometry. For quantification, matrix-matched standards or matrix-correction calculations are necessary. Quantitative XRF makes ample use of calibration standards (now available with the calibrating power of some 200 international reference materials). Table 8.41 shows the quantitative procedures commonly employed in XRF analysis. Quantitation is more difficult for the determination of a single element in an unknown than in a known matrix, and is most complex for all elements in an unknown matrix. In the latter case, full qualitative analysis is required before any attempt is made to quantitate the matrix elements. 

Harvey, P.H. and Pagel, M.D. (1991) The Comparative Method in Evolutionary Biohgy. Oxford University Press, Oxford. 

Nonspecific protein binding to the solid phase complicates the method and is a selective pressure driving its evolution. The adaptive response has been the development of intrinsically comparative methods in which specific binding to an immobilized ligand is blocked in one out of two otherwise identical samples. When the respective protein components of the samples are compared, specifically bound proteins are present in one but severely depleted in the other. To allow relative quantitation, the two samples can be made isotopically distinct by a chemical or metabolic process and then mixed for an analytical step that avoids intersample variability [15]. 

Kaisheva A., Iliev I., Gamburzev S., Comparative methods fo estimation of the activity and the transport hindrances of air gas-diffusion electrodes, J.Power Sources, 1984 13 181 - 195. 

Table 35-4 ANOVA comparing methods for combined laboratories and operators, all Method B vs. all Method A...

Analytical results comparing METHOD B and METHOD A will show significant variation due to the high precision of both analytical methods. 

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