Separ ation techniques

The pur pose of work is to develop the technique of separ ation of purine bases (caffeine, theophylline, theobromine) and the technique of detection of purine bases in biological fluid by TLC using micellar mobile phases containing of different surfactants. 

Many different combinations, separation -i- element-selective detection, have been attempted but HPLC in conjunction with ISP-MS has emerged as one of the best combinations. HPLC is a versatile technique, which due to the vai iety of sepai ation mechanisms developed, can be applied to a great vai iety of medically important analytes. 

Two separate experimental approaches, diffuse reflectance and photoluminescence spectroscopy, were then taken both led to similar results. The latter technique is the more sensitive, and well-resolved spectra can often be observed, but only when a radiative decay of the excited state occurs. The diffuse reflectance spectra are broader in scope but the absorption bands appear as shoulders. The reflectance spectra of alkaline earth oxides were examined by Zecchina et al. (77, 78), Garrone et al. (79), and Zecchina and Scarano (80), but an overpressure of a quenching gas (usually oxygen) had to be used to suppress the fluorescence and to allow observ ation of the reflectance absorption bands (Fig. 10). In addition to usual bands in the U V region due to bulk excitations (bulk cxcitons), new absorption bands which correspond to excitations localized on the surface ions are present. 

There is an EXAFS report on the hydroxylase component of the MMO from Methylobacterium CRL-26 that shows an average Fe-L distance of 1.92 A and an Fe-Fe separation of 3.05 A (42). The tack of a short Fe-p,-0 bond is consistent with the apparent absence of an oxo bridge based on other techniques, while the presence of a Fe scatterer at 3.05 A corroborates the dinuclear nature of the site. However, the apparent lower purity of the sample as indicated by the observ ation of metalloporphyrin-like absorption features in the visible spectrum and the later report by Ericson et al. (52) that MMO from M. capsulatas (Bath) is photoreduced in the synchrotron beam raise doubts about the reliability of these results. 

Where the components of a mixture differ greatly in degree of methyl-ation, temperature programming may be used with advantage, and may be started at as low as 50°. Even with the use of this technique, there are some compounds not readily separated as alditol acetates, and for which other derivatives are preferable thus, 2- and 3-O-methylxyloses are not separable as the alditol acetates, but are resolved as the tri-methylsilyl derivatives. With mixtures of unknown composition, it is thus prudent to investigate the separation by trying different derivatives. 

Electrophoretic techniques are generally used for separation of charged analytes. Charged analytes move in electrolyte solutions when an electrical field is estabhshed. Separation is obtained if the charged analytes have different m ation velocity. The electrolyte solution is most commonly a mixture of weak acids and bases in water. 

Martel et al. investigated phase separation in glasses which occurs in silica-rich glasses however, some aspects as the first steps of the nucle-ation of domains with different compositions remain to be clarified as they are diffieult to eharacterize with most analytical techniques. studies and 2D Si- Si eorrelation experiments were used to characterize the Si-O-Si network after various heat treatments and are used to obtain the compositions of the two demixing phases. ... 

In the various sections of this chtqiter, I will briefly describe the major characteristics of FT-IR, and then relate the importance of these characteristics to physiochemical smdies of coUoids and interfaces. This book is divided into two major areas studies of "bulk" colloidal aggregates such as micelles, surfactant gels and bilayers and studies of interfacial ptenomena such as surfactant and polymer adsorption at the solid-liquid interface. This review will follow the same orgar ation. A separate overview cluq>ter addresses the details of the study of interfaces via the attenuated total reflection (ATR) and graang angle reflection techniques. 

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