Absorption detectors data analysis

Time-Resolved Absorption Spectroscopy Advantages, 232, 389 applications, 232, 387-388 detectors, 232, 387, 392-393, 399 hemoglobin data analysis, 232, 401-415 kinetic analyses, 232, 390 photoselection effects, 232, 390-391 kinetic intermediates and. 

It is practical to carry out analysis on on-line systems with two detectors. Since quantitative capabilities of UV-Vis absorption spectroscopy are typically greater than those of MS, in some protocols, UV absorption detectors are used to carry out quantitative analysis (after separation on a chromatographic column) while MS data are used for qualitative analysis (peak assignment) [3]. In one study, the effluent from a high-performance liquid chromatography (HPLC) instmment was transferred to the UV detector. After UV detection, the flow was split, and part of it was transferred to the ESI-MS system [4]. Using LC separations coupled with UV and MS is also useful in the characterization of products of electrochemical reactions, and considered complementary to on-line monitoring [5, 6]. 

Solvent — The transition energy responsible for the main absorption band is dependent on the refractive index of the solvent, the transition energy being lower as the refractive index of the solvent increases. In other words, the values are similar in petroleum ether, hexane, and diethyl ether and much higher in benzene, toluene, and chlorinated solvents. Therefore, for comparison of the UV-Vis spectrum features, the same solvent should be used to obtain all carotenoid data. In addition, because of this solvent effect, special care should be taken when information about a chromophore is taken from a UV-Vis spectrum measured online by a PDA detector during HPLC analysis. 

The aim of all the foregoing methods of factor analysis is to decompose a data-set into physically meaningful factors, for instance pure spectra from a HPLC-DAD data-set. After those factors have been obtained, quantitation should be possible by calculating the contribution of each factor in the rows of the data matrix. By ITTFA (see Section 34.2.6) for example, one estimates the elution profiles of each individual compound. However, for quantitation the peak areas have to be correlated to the concentration by a calibration step. This is particularly important when using a diode array detector because the response factors (absorptivity) may considerably vary with the compound considered. Some methods of factor analysis require the presence of a pure variable for each factor. In that case quantitation becomes straightforward and does not need a multivariate approach because full selectivity is available. 

Methods. Absorption spectra were recorded using an Hitachi model 150-20 spectrophotometer/data processor system. Uncorrected steady-state fluorescence emission spectra were recorded using a Perkin-Elmer MPF-44A spectrofluorimeter. These spectra were collected and stored using a dedicated microcomputer and then transferred to a VAX 11/780 computer for analysis. Fluorescence spectra were corrected subsequently for the response characteristics of the detector (21). Values of the fluorescence quantum yield, <) , were determined relative to either quinine bisulfate in IN H2S04 )>f =... 

A consistent protocol for the collection and analysis of thin-film EDS data requires an assessment of both instrument and specimen dependent parameters. Major parameters which should be considered for thin-film analyses include spurious X-rays, spectral artifacts, detector geometry, probe diameter, beam broadening, contamination, sample preparation artifacts, sample orientation and temperature and X-ray absorption. Many of these parameters are interdependant during an analysis and the prudent operator will evaluate as many as possible before routine use of an AEM. Further explanations of these parameters can be found in a number of publications [4,6.,9.,7] Only selected parameters are discussed below. 

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