UV-absorbing species

The sulfuric acid treated aliquot representing the blank forms a cyclic ether anhydroerythromycin.10 The alkaline treatment causes the formation of an unsaturated ketone (9-keto-10-ene) having its absorbance maximum as a shoulder at 236 nm. (e 6000).n i2 Thus, any other UV absorbing species are measured with the blank and subtracted from the absorbance before calculation of the erythromycin concentration. A typical spectrum is shown in Figure 4. 

While the alkyl chain distribution is determined on a non-polar RP8 and RP18, EO homologue distribution is determined using a polar phase. AEOs are not UV-absorbing species, so they cannot be directly determined by HPLC followed by standard optical detection systems (UV and FL), unless suitable derivatives are prepared [2], Because of this, methods based on liquid chromatography-mass spectrometry [77-79] are currently considered as the benchmark procedure that gives sufficiently high selectivity and sensitivity. 

The loss of absorption with cleavage of the (3-lactam was used by Marrelli to analyze the concentrations of cephalosporin C in the presence of other UV absorbing species. 

Kuban P, Abad-Villar EM, Hauser PC. Evaluation of contactless conductivity detection for the determination of UV absorbing and non-UV absorbing species in reversed-phase high-performance liquid chromatography. Journal of Chromatography A 1107, 159-164, 2006. 

Fluorescence is subject to interference by UV absorbing species, heavy ions in solution, and is affected by temperature. 

An ultraviolet (UV) spectrum of an aqueous rubber extract identifies and quantifies the antioxidants, curing agents, accelerators, and other UV-absorbing species extracted from the compound. 

One ml of 0.5 NaOH is added to neutralize the acid-treated standard, which is then processed as indicated for the other two aliquots of standard starting with the addition of alkali reagent. The acid-treated standard represents the standard blank. The H SO is used to destroy the erythromycin base, making it possible to measure any absorbance in the blank that may be due to excipients. Solutions of erythromycin base have negligible UV absorbance, but the alkali reagent and heat convert erythromycin to a UV-absorbing specie. 

Chemically bonded aminopropyl phases have also been successfully employed for the separation of inorganic ions. Leuenberger et al. [19] described the separation of nitrate and bromide in foodstuffs on such a phase using a phosphate buffer solution as the eluent. These alternative techniques are also described in Chapter 5. However, it is presently very difficult to comment on their potential for universal applicability, since they have mainly been used for the analysis of UV-absorbing species. 

It can also be used to detect non-UV-absorbing species in an eluent with high absorbance (inverse detection). 

Transient absorption spectra of some "satellite ions" closely resemble the spectra of olefin radical cations. In cyclohexane, a band centered at 270 nm (at 2 ns [22]) is observed from 250 ps [25] after the ionization event (this band overlaps with the strong 240 nm band of cyclohexyl radicals [22]). The scavenging behavior and the decay kinetics of the UV-absorbing species suggest that they are normally-diffusing radical cations [25]. In the first few nanoseconds after the ionization event, the VIS absorbance is dominated by solvent excited states [22,57]. When the thermalized electrons are rapidly scavenged using a suitable electron acceptor (halocarbons or N2O), this... 

S-states. In particular, the feature near 350 nm with an absorbance amplitude sequence of (+/+/+/—) is assigned to the Mn4 cluster and not other UV absorbing species, such as the quinones. The electronic nature of the absorption is unclear, although detailed analysis of the absorption spectra of model Mn-oxo complexes suggests that these are metal-centered d-d or ligand-to-metal (oxo-to-Mn) charge transfer bands. This absorption feature is useful for monitoring the kinetics of... 

A major limitation in the increased application of modern liquid chromatography is the sensitivity of the detector system (70,71). For example, although a few UV detectors have been described which are usable at low nanogram levels, these involve special operating conditions or compounds with higher molar absorptivities (70,72,73). With ordinary UV absorbing species, quantitative LC is usually limited to a few tenths of micrograms (7],). 

Our data for the distribution of irregular structures as a function of MW do not support recent interpretations (40) based on a close correlation between bimodal MWD and amounT of fast side reactions. If irregularities were prevailing in the initial stage of polymerization, when higher molecular weights are pro -duced, the amount of uv absorbing species would be a function of the chain size. A more detailed interpretation of the correlations... 

Comonomer Concentrations An important innovation made by the addition of a full spectrum UV spectrophotometer into ACOMP detector train led to the determination of the instantaneous concentration of each comonomer during the reaction, in the case of the copolymerization of comonomers with similar spectral characteristics [19, 20], The working assumption was that a UV spectrum at any instant is a Unear combination of the normalized basis spectra of the comonomers, the copolymer, and any other UV absorbing species, and that the unknown comonomer concentrations can be foimd by minimizing the error between measured and computed spectra over many wavelengths, even when spectral diffaences are small at any iven wavelength. 

It was not possible to perform any qualitative or quantitative determinations via HPLC-Uy because the presence of other UV absorbing species in the elution regions of the Se species prevented their detection (Fig. 9.16). Without further sample work-up and preparation, it was not possible to utilize any form of UV detection with these particular HPLC conditions for either Se species in these samples. In contrast, the HPLC-... 

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