UV chromophores

Detection of the these types of compounds are sometimes difficult as many components of cosmetic products are aliphatic, do not possess a UV chromophore and are not easily reacted to give fluorescent derivatives. Providing the concentration of the component of interest is sufficiently high, then a refractive index detector is often used. If... 

The reaction was also chosen for analytical reasons as the pyrazole ring is a good UV chromophore, facilitating analysis [20]. 

To compare the disassembly rate of the above dendritic systems, we synthesized AB3 molecules 18 and 19 (Fig. 5.10). Both the molecules are designed for activation by PGA and have three units of tryptophan as a model drug. Tryptophan was used for initial evaluation as it contains a strong UV chromophore, allowing us to monitor the disassembly reaction. 

A method suitable for quantification of the functional class of bis(ethanol)amine antistatics, which lack UV chromophores, consists of reaction with methyl orange [53]. Atmer 163 (alkyl-diethanol amine) has been determined as a yellow complex at 415 nm after interaction with a bromophenol/cresole mixture [64]. Hilton [65] coupled extracted phenolic antioxidants with diazotised p-nitroaniline in strongly acidic medium and carried out identification on the basis of the visible absorption spectrum in alkaline solution. The antioxidant Nonox Cl in... 

Since many new substances of interest are very poorly soluble in water, the assessment of the pKa in aqueous solution can be difficult and problematic. Potentiometry can be a quick technique for such assessment, provided the solubility of the substance is at least 100 pM. (Solutions as dilute as 10 pM can still be analyzed, but special attention must be given to electrode calibration, and ambient carbon dioxide must be excluded.) If the substance is soluble to only 1-10 pM and possesses a pH-sensitive UV chromophore, then spectrophotometry can be applied. CE methods may also be useful since very small sample quantities are required, and detection methods are generally quite sensitive. 

Detection in 2DLC is the same as encountered in one-dimensional HPLC. A variety of detectors are presented in Table 5.2. The choice of detector is dependent on the molecule being detected, the problem being solved, and the separation mode used for the second dimension. If MS detection is utilized, then volatile buffers are typically used in the second-dimension separation. Ultraviolet detection is used for peptides, proteins, and any molecules that contain an appropriate chromophore. Evaporative light scattering detection has become popular for the analysis of polymers and surfactants that do not contain UV chromophores. Refractive index (RI) detection is generally used with size exclusion chromatography for the analysis of polymers. 

The pH-metric method is an important reference method because it can be used to measure all pKas between 2 and 12, with or without a UV chromophore, provided that the sample can be dissolved in water or water/co-solvent over the pH range of interest. In this method, the sample solution is titrated with acid or base, the titration is monitored with a glass pH electrode, and the pKa is calculated from the... 

LFP gives us the time resolution needed to follow the kinetic evolution of many carbenic reactions.9 However, if the carbene lacks a readily accessible UV chromophore, its reactions must either be followed indirectly or, as has recently become practical, by LFP with IR detection of the carbenic intermediates.10... 

In the 1988-1999 period, almost all absolute kinetic studies of carbenic reactions employed LFP with UV detection. Carbenes that contain a UV chromophore (e.g., PhCCl) are easily observed, and their decay kinetics during reaction can be readily followed by LFP.11 However, alkyl, alkylhalo, and alkylacyloxycarbenes are generally transparent in the most useful UV region. To follow their kinetics, Jackson et al. made use of the ylide method, 12 in which the laser-generated carbene (2) is competitively captured by (e.g.) pyridine, forming a chromophoric ylide (3, cf. Scheme 1). The observed pseudo first order rate constants (kobs) for the growth of ylide 3 at various concentrations of pyridine are monitored by UV spectroscopy, and obey Eq. 1. 

Antibodies produced by this procedure were screened for their ability to react with the hapten to form the vinylogous amide 6, which has a convenient UV chromophore near 318nm, clear of the main protein absorption. Two antibodies selected in this way catalysed the expected aldol reaction of acetone with aldehyde 7 by way of the enamine 8 (Scheme 3) the remainder did not. These two effective aldolase mimics have been studied in some detail, and a crystal structure is available for (a Fab fragment of) one of them.126,281... 

Aromatic alcohol clusters have been well-studied, also for methodical reasons. The UV chromophore can be exploited for sensitive detection of the IR spectrum [35, 36, 120, 179]. Time-domain experiments become possible [21], which show that the initial energy flow out of the O—H stretching mode occurs primarily via C—H stretching and bending doorway states. Like in the case of carboxylic acid dimers [245], the role of the hydrogen bond is to shift the O—H stretching mode closer to these doorway states and thus to accelerate the initial energy flow. 

Pharmaceutical substances lacking an UV-chromophore in the 254 nm region but possessing areactive functional group,... 

Another ion chromatography pharmaceutical application is the analysis of amines and amphoteric compounds such as choline (see Figure 19). Such compounds may be present either as counterions, as mentioned above, or as synthesis by-products. In either case, ion chromatography can be advantageously utilized for this class of compounds due to the limited utility of gas chromatography and the lack of a UV chromophore for such compounds. Again, screening for such compounds in pharmaceutical preparations can be best accomplished... 

Non-aqueous CE In organic solvent chargeable, in solvent system soluble compounds, mainly with UV chromophore HPLC... 

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