Peak with multichannel detection

The single crystal of gas hydrate prepared from H2 + CO2 and H2 + CO2 + THF mixtures was analyzed by in situ Raman spectroscopy using a laser Raman microprobe spectrophotometer with multichannel CCD detector. In the present study, the single crystal was defined as the gas hydrate crystal for which the Raman peak of the intermolecular 0-0 vibration mode can be detected. The argon ion laser beam (wavelength 514.5 nm, power 100 mW) or He-Ne laser beam (wavelength 632.8 nm, power 35 mW) condensed to 2 pm in spot diameter was irradiated to the sample through the upper sapphire (or quartz) window. The backscatter of the opposite direction was taken in with the same lens. The spectral resolution was about 1 cm ... 

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

More detailed results take into account a wall effect to explain why elution profiles are skewed, even for non-retained solutes in modem columns. Detailed experimental results were recently presented by Farkas and Guiochon on the radial distribution of flow velocity using local multichannel detection devices. On average, the flow velocity is very homogeneous in the center of the column, but, inevitably, it becomes lower near the walls. Similarly, the peak shape from a local microdetector situated near the wall is clearly distorted and skewed compared with that of a similar detector situated near the center of the column. 

There are several potential sources of radioactive materials that can contaminate water (see Chapter 4, Section 4.14). Radioactive contamination of water is normally detected by measurements of gross P activity and gross a activity, a procedure that is simpler than detecting individual isotopes. The measurement is made from a sample formed by evaporating water to a very thin layer on a small pan, which is then inserted inside an internal proportional counter. This setup is necessary because P particles can penetrate only very thin detector windows, and a particles have essentially no penetrating power. More detailed information can be obtained for radionuclides that anit y-rays by the use of gamma spectrum analysis. This technique employs solid-state detectors to resolve rather closely spaced y peaks characteristic of specific isotopes in the sample s spectra. In conjunction with multichannel spectrometric data analysis, it is possible to determine a number of radionuclides in the same sample without chemical separation. This method requires minimal sample preparation. 

A remaining problem for all spectrometric peak recognition methods is the reproducibility of the spectra recorded under different chromatographic conditions. For example, if the differences between the UV spectra for a given solute induced by variations in the mobile phase in RPLC are larger than the differences between the UV spectra of different solutes recorded under identical conditions, then clearly the application of multichannel UV detection, with or without the use of PCA techniques, will be of limited use. 

Fig. 4. Schematic representation of a commercial parallel LC/MS system. Liquid flow is delivered to eight columns by a pump and a flowsplitter. Peaks are detected by a multichannel UV detector and a TOF mass spectrometer with a multiplexed electrospray source...

Frequently, one must be able to identify the residual full-energy sum peaks in a spectrum and subtract their contribution from analyte lines with which they interfere. The following equations can be useful for this task. The equations are valid for the case where the peak amplitude detection time Tp is constant and independent of pulse height. Depending on multichannel analyzer design, this condition may or may not be met at very low pulse heights. The case of Tp being a function of pulse amplitude is discussed in Sec. 4.6. 

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