UV-absorbing chromophore

The dissolution of macromolecules is a prerequisite for the application of liquid chromatography for their separation and characterization. Compared to HPLC of small molecules, concentration of the polymer solutions injected into the analytical HPLC columns is higher and usually assumes lmg mL and more. This is mainly due to detection problems the detectors used in polymer HPLC are much less sensitive (Section 16.9.1) than detectors for small molecules, which often carry the UV-absorbing chromophores. This means that samples subject to polymer HPLC must exhibit rather high solubility. 

Aminoglycosides are basic, thermally labile, hydrophilic compounds that do not contain analytically useful UV-absorbing chromophores. Therefore pre- or postcolumn derivatization is necessary for their UV or fluorescence detection. 

Method 2 (phenol-sulfuric acid reaction). The reaction of carbohydrates with phenol in the presence of sulfuric acid produces a UV-absorbing chromophore which is sufficiently sensitive to be used as a means of detecting less than 1-pg amounts of carbohydrates... 

Method 3 (sulfuric acid treatment). A similar system to that mentioned above (Method 2) has been modified so that only sulfuric acid is used to produce UV-absorbing chromophores in the column effluent [47]. The effluent (flow-rates, 10—12 ml/h) is mixed with sulfuric acid at 19 ml/min, in a chamber of the type mentioned in Method 2. The mixed effluent is passed through a heating area at 100 °C for 2 min before being measured photometrically at 306 nm. The limits of detection are of the same order as those shown in Table 4.7. 

An artificial substrate labeled with a strong UV-absorbing chromophore was synthesized. This substrate and its product, obtained by hydrolysis of the ADP-ribosyl moiety, were separated on a Zorbax-ODS reversed-phase CI8 column (4.6 mm X 250 mm). The initial mobile phase was 70% 0.0435 M sodium acetate (pH 4.0) and 30% acetonitrile. The percentage of acetonitrile... 

The disadvantages of HPLC centre around the detection systems available. Ultraviolet spectrometers are most commonly used detectors but they require that the compound has a UV absorbing chromophore. Variable wavelength UV spectrophotometers offer reasonable versatility, but some steroids and other drugs must be derivatized before UV detection is possible. With the introduction of electrochemical and spectrophotometric detection in region other than the ultraviolet, and the rationalization of mobile phase delivery systems by the use of microprocessor control, capabilities of HPLC have significantly increased. 

Indirect methods can also use mass spectrometers as detectors. As noted above fragmentation is a potentially severe problem that must be taken into consideration. Both continuous and pulsed beam techniques can be used. A particularly novel approach has been developed using multiphoton ionization via a favorable UV-absorbing chromophore. Neutral clusters are formed containing the readily ionizable molecule, but the weak interactions between the chromophore and the rest of cluster reduces the extent... 

Such resins may be used in combination with the simpler methacrylate monomers to improve the performance of the cured product. Their relative involatility and the presence of a UV-absorbing chromophore make LC the preferred approach for analysis. Again the use of an internal standard is favored for quantitation purposes. 

Detection with MS is particularly important for the isolation of compounds that lack useful chromophores or are found only in complicated mixtures such as lactose [56]. The lack of a UV-absorbing chromophore in the saccharide structure limits the mode of detection. Refractive index detection requires precise control of the mobile phase and often does not meet the demands of trace-level analysis needed concerning sensitivity and selectivity. Even chemical derivatization, for example, postcolumn derivatization and enzymatic derivatization, which greatly improves the selectivity and sensitivity of a chromatographic detection systan, does not meet the needed trace levels for the detection of the fine particle dose of lactose. The reason... 

The sources of the UV-absorbing chromophores come from the chemical structure of the pol5uner, the thermal processing degradation products, colorants, fillers, other additives such as halogenated flame retardants, antioxidants and their transformation products, feedstock or process impurities, and residual catalyst. 

UV. Due to the UV absorbing chromophores in the molecule of dactylarin, visualization of the spots could be achieved by the luminescent indicator method using silica gel foils with an inert luminescent indicator (Silufol UV2,4 Lachema, Brno, Czechoslovakia) spots were then visualized under UV light Rf... 

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