Analysis, proximate quantitative

Another definition of the term chemical analysis is also worth mentioning. The dictionary definition as found in Vogel s Textbook of Quantitative Inorganic Analysis says that chemical analysis is The resolution of a chemical compound into its proximate or ultimate parts the determination of its elements or of the foreign substances it may contain . 

The dynamics of proton binding to the extra cellular and the cytoplasmic surfaces of the purple membranes were measured by the pH jump methods [125], The purple membranes selectively labeled by fluorescein Lys-129 of bacteri-orhodopsin were pulsed by protons released in the aqueous bulk from excited pyranine and the reaction of the protons with the indicators was measured. Kinetic analysis of the data implied that the two faces of the membrane differ in then-buffer capacities and in their rates of interaction with bulk protons. The extracellular surfaces of the purple membrane contains one anionic proton binding site per protein molecule with pA" 5.1. This site is within a Coulomb cage radius from Lys-129. The cytoplasmic surface of the purple membrane bears four to five pro-tonable moieties that, due to close proximity, function as a common proton binding site. The reaction of the proton with this cluster is at a very fast rate (3 X 1010 M-1 sec ). The proximity between the elements is sufficiently high that even in 100 mM NaCl, they still function as a cluster. Extraction of the chromophore retinal from the protein has a marked effect on the carboxylates of the cytoplasmic surface, and two to three of them assume positions that almost bar their reaction with bulk protons. Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk has been done by using numerical... 

A major difficulty with this analysis, however, is that the assumption AS t % 0 requires that the solvation environment of the transition state is unaffected by its proximity to the electrode surface (Sect. 3.4). Stated equivalently, it is often expected that the temperature-dependent work terms required to extract kscorr from k ob contain large components from short-range solvation and other factors in addition to the usual "electrostatic doublelayer effects (Sect. 2.4 and 4.6). As noted in Sect. 2.3, the situation is somewhat more straightforward for surface-attached reactants since then the effects of work terms at least partly disappear. This question underscores the inevitable difficulties involved in extracting quantitative information on electron-transfer barriers from rate measurements. 

McDonald-Taylor et al. 1997. Uranyl nitrate-induced proximal tubule alterations in rabbits A quantitive analysis. Toxicologic Pathology 25(4) 381-389. 

Fig. 6. Effective stress has been color coded for its proximity to the hydraulic seal failure limit of 1000 psi. Green represents a low likelihood of seal failure. Yellow indicates uncertainty based on an analysis of the estimated error in effective stress. Certain basins stand out as either low risk (e.g.. Auger basin) or high risk (e.g., Amundsen basin). The updip margins of most basins show high risk in prospectivity. This allowed explorationists a quantitative means of not only highgrading prospects in this fairway but also opening new opportunities. The inset shows the extent of the area of study in the Gulf of Mexico.

The IMER approach does not require that the enzyme be placed in close proximity to the detector if the transducer signal is generated by a soluble product or cosubstrate of the enzymatic reaction. In the latter case, a variety of flow systems and postreactor detectors can be utilized to produce simultaneous determinations of the concentrations of several analytes. For example, an IMER can be combined with a high-performance liquid chromatography (HPLC) instrument (perhaps also in combination with mass spectroscopy) for purposes of both qualitative and quantitative analysis. The chemo-, stereo-, and regio-selectivities of enzymes facilitate separation and/or identification of analytes that may be present as different isomers (e.g., in peptide analysis based on use of peptidase IMERs in combination with these techniques to obtain structural information about the sequence of amino acids in peptides). 

Solid-state MAS NMR spectroscopy has had much success in examining amorphous insoluble polymers [59]. In recent years, however, there has been some debate on the reliability of quantitative data derived from CP experiments [60] and work on fossil fuels in particular has highlighted the problem [61,62]. Undoubtedly, the issues arise in the analysis of polymers as well [63-66]. While CP results in signal-to-noise enhancement and hence reduced accumulation times, carbon atoms present with no proximal protons tend to have their peak intensities reduced relative to other signals. Quaternary aromatic carbons are likely to suffer badly in this respect. The modulation of the dipolar interactions by the motion of some moieties can also introduce quantitative errors [67]. The rotation of the methyl group about its 3-fold axis of symmetry is a good example of this. Single pulse excitation (SPE) [60] however overcomes the problems that are associated with CP,... 

The results of the quantitative analysis of the elements C, Si, S, Mo, Ni, Fe, and V by combustion and XRF analysis are given in Table 8 for six samples that were on stream for 10 months [the sample number is directly related to the proximity of the sample to the reactor inlet (1 = closest to inlet, etc)]. Comparison of these results to corresponding results in the absence of added PDMS (not shown here) suggests that silica alone is responsible for the rapid and irreversible deactivation." ... 

It is often necessary in the analysis of a mixture of compounds to determine the proportions in which the constituents of the mixture are present. Many natural products used as foods or drugs, or in the manufacture of paints, dyes, etc., are mixtures in which compounds of known composition are present in varying proportions. Thus, milk contains water, fat, inorganic salts, and organic nitrogen compounds. The quantitative determination of the constituents of such mixtures is called proximate analysis. Many methods have been applied in this branch of quantitative analysis. They are based on the physical and chemical properties of the compounds which constitute the mixtures. A few typical methods are described in the chapter in which fats and oils are discussed. 

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