Classical quantitation

Classically, quantitation by fluorimetry is done using a calibration curve obtained with reference solutions or by using a single point calibration. In the latter case, the unknown concentration is given by ... 

Andrade CH, Salum Lde B, Castilho MS et al (2008) Fragment-based and classical quantitative structure-activity relationships for a series of hydrazides as antituberculosis agents. Mol Divers 12 47-59... 

Classical Quantitative Structure-Activity Relationship Techniques The early QSAR models for calcium channel ligands were based on classical Hansch analysis and elucidated the structural requirements for the binding of molecules to their receptors [111-115], It was found that various steric (Bl, L), electronic (a), and hydrophobic (n) parameters or their combination correlated well with the potency of various DHPs [111]. QSAR analysis of another set of DHPs revealed good correlations between electronic properties (F-constants) of the phenyl ring substituents and binding affinities or functional potency [112] lipophilicity as well as ortho- and meta-substituents inductivity... 

Classically, quantitative internal QC involves the analysis of a sample for which the analyte concentration is known, either because the material has been analyzed on many occasions and the distribution of I esults documented, or because it has been analyzed independently and the mean and range of results quoted for the method used. The essence of using the internal QC material is to establish the interval of results that is acceptable the current analytical result is compared with the interval of results deemed to be acceptable (see Chapter 16). The result must then be documented, usually graphically, because it shows the conformity of results and any trends m results that may be occurring. The major aim is to use a means of documentation that ensures that comparative performance is assessed. 

The classic quantitative biochemical method for assaying steroid receptors in tumor tissue specimens is the multiple-point dextran-coated charcoal (DCC) titration assay. However, in comparison with the classic DCC assays, enzyme immunoassays are preferred as they cost less and are simpler, require less time, and can be performed using less tissue than DCC titration assays. 

The classical quantitative calculations of interaction forces in thin liquid films were made during the second world war hy Deijaguin Landau (1941) and in a monograph by Verwey Overbeek (1948). This theory for thin liquid films is therefore known as the Derjaguin, Landau, Verwey and Overbeek theory (DLVO). 

Examination of the literature discloses very few examples of classical quantitative elemental analysis. ESCA is an extraordinarily sensitive surface technique involving the top twenty or so angstroms in this sense, almost vanishingly small amounts of an element, about 0.001 monolayer, can be detected. To attempt an elemental analysis of a sample, however, immediately presents the analyst with the question of how representative the surface is of the rest of the sample, particularly in view of the possibility of surface contamination. Sample preparation is critical and must contend with a wide variety of surface phenomena such as adsorption and chemisorption, oxidation, and mechanical contamination, as well as more subtle phenomena that will be brought out in greater detail below. One important point is that both ESCA and Auger spectroscopy are essentially nondestructive techniques. 

To separate and purify the radionuclide of interest in the sample, the analyst can depend on the similar behavior of the stable element and its radioisotopes. Chemical reactions involving the radionuclide will proceed with essentially the equilibrium and rate constants known for the stable element in the same chemical form. Slight differences result from small differences between the isotopic mass of the radionuclide and the atomic mass (i.e., the weighted average of the stable isotopic masses) of the stable element. Because of this similarity in chemical behavior, many ra-dioanalytical chemistry procedures were adapted from classical quantitative and qualitative analysis. For the same reason, new methods published for separating chemical substances by processes such as precipitation, ion-exchange, solvent extraction, or distillation are adapted for and applied to radionuclides. One exception occurs when the radionuclides to be separated are two or more isotopes of the same element. Here, effective separation can be accomplished by mass spectrometer (see Chapter 17). 

It is worth noting that in classical quantitative analysis, which usually did not Involve analyses of trace amounts, the problem of unknown Interferences was attacked by using two methods that were as nearly Independent as possible. In that way, the chance that an Interference would give the same response for each method was minimal. In contrast, there is an example in clinical chemistry which clearly suffers from a lack of selectivity in the accepted method. Figure 2 (11) shows that the use of the determination... 

Like all classical quantitative analysis methods, NMR spectroscopy needs calibration, calibration standards and a validation procedure. The standard techniques are used for calibration external calibration, the standard addition method and the internal standard method. A fourth is a special NMR calibration method, the tube-in-tube technique. A small glass tube (capillary) containing a defined amount of standard is put into the normal, larger NMR tube filled with the sample for analysis. In most cases, there are slight differences in the chemical shift of corresponding signals of the same molecule in the inner... 

Figure 1 Stages for classical Quantitative structure-activity/property relationship (QSAR/QSPR) development.

UV-Vis absorption is essentially a classical quantitative tool for organic compounds, but a good level... 

Multiwavelength methods. Least squares curve fitting techniques may be used in the determination of multicomponent mixtures with overlapping spectral features. Two classical quantitation methods, the Classical Least Squares (CLS) mode and the Inverse Least Squares (ILS) model, are applied when wavelength selection is not a problem. CLS is based on Beer s law and uses large regions of the spec-tram for calibration but cannot cope with mixtures of interacting constituents. ILS (multivariate method) can accurately build models for complex mixtures when only some of the constituent concentrations are known. 

Duckworth [131] and others [132] have reviewed quantitative spectroscopic analysis, including evaluations of classical quantitation methods (LSR, CLS, ILS) and eigenvector quantitation methods (PCR, PLS, factor analysis). Another useful review dealing with chemometrics (to spectra) is ref. [137]. 

Before attempting to deduce the structure of an unknown organic compound from an examination of its spectra, we can simplify the problem somewhat by examining the molecular formula of the substance. The purpose of this chapter is to describe how the molecular formula of a compound is determined and how structural information may be obtained from that formula. The chapter reviews both the modem and classical quantitative methods of determining the molecular formula. While use of the mass spectrometer (Chapter 3) can supplant many of these quantitative analytical methods, they are still in use. Many journals still require that a satisfactory quantitative elemental analysis (Section 1.1) be obtained prior to the publication of research results. 

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