Spectroscopic techniques detectors

Combined chromatographic-spectroscopic techniques allow complex multicomponent data to be obtained in a single experiment. Essentially, the analysis of monomers, additives, oligomers and polymer can be performed in one step on-line. Postcolumn hyphenation, which comprises spectroscopic detectors, sniffing, fraction collection or heartcutting, is well... 

In polymer/additive analysis, spectroscopic methods are used for studying both molecular and atomic composition, usually as a detector for chromatographic techniques. Application of spectroscopic techniques to molecular additive analysis depends on the nature of the sample and its complexity (Table 10.26). Application of the intrinsically simple monocomponent analyses by means of UV/VIS and FUR is rather exceptional for real-life samples. Most industrial samples are complex. It is in the area of multicomponent analysis that most... 

The same can be said for the sections concerning the instrumental techniques of GC, IR, NMR, and HPLC. The chromatographic techniques of GC and HPLC are presented as they relate to thin-layer and column chromatography. The spectroscopic techniques depend less on laboratory manipulation and so are presented in terms of similarities to the electronic instrumentation of GC and HPLC techniques (dual detectors, UV detection in HPLC, etc.). For all techniques, the emphasis is on correct sample preparation and correct instrument operation. 

The response function and the associated analytical merits for absorption spectroscopic techniques (e.g., NIR, UV-vis and infrared) are determined by the optical path length, detector gain, signal averaging and spectral resolution. The LIF detection performance is also governed by these parameters but is also influenced by critical parameters associated with the excitation source (e.g., optical power, pulse rate, etc.) as previously discussed. ... 

Tunable laser spectroscopic techniques such as laser-induced fluorescence (LIF) or resonantly enhanced multi-photon ionization (REMPI) are well-established mature fields in gas-phase spectroscopy and dynamics, and their application to gas-surface dynamics parallels their use elsewhere. The advantage of these techniques is that they can provide exceedingly sensitive detection, perhaps more so than mass spectrometers. In addition, they are detectors of individual quantum states and hence can measure nascent internal state population distributions produced via the gas-surface dynamics. The disadvantage of these techniques is that they are not completely general. Only some interesting molecules have spectroscopy amenable to be detected sensitively in this fashion, e.g., H2, N2, NO, CO, etc. Other interesting molecules, e.g. 02, CH4, etc., do not have suitable spectroscopy. However, when applicable, the laser spectroscopic techniques are very powerful. 

National Laboratory by several standard spectroscopic techniques, including the measurements of angular correlations by a fixed-four detector system, y-y and 8-y coincidence, and lifetimes of some excited states. 

Near-infrared chemical imaging using multichannel detectors inherits many of the attributes of conventional NIR spectroscopy using a single-channel detector. In addition to its well-documented capabilities as a spectroscopic technique, in comparison to other vibrational imaging approaches, it has unparalleled flexibility in terms of managing widely varying sample size, placement, shape and color. As has been shown with the three examples presented in this chapter, the technique easily... 

Spectroscopic detectors measure partial or complete energy absorption, energy emission, or mass spectra in real-time as analytes are separated on a chromatography column. Spectroscopic data provide the strongest evidence to support the identifications of analytes. However, depending on the spectroscopic technique, other method attributes such as sensitivity and peak area measurement accuracy may be reduced compared to some nonselective and selective detectors. The mass spectrometer and Fourier transform infrared spectrometer are examples of spectroscopic detectors used online with GC and HPLC. The diode array detector, which can measure the UV-VIS spectra of eluting analytes is a... 

Photoacoustic spectroscopy A spectroscopic technique based on the photoacoustic effect. A photoacoustic spectrum consists of a plot of the intensity of the acoustic signal detected by a microphone or a piezoelectric detector, against the excita-... 

Improvements in column technology, detector sensitivity and the development of new detection systems, have made possible the routine separation of picomole quantities of nucleic acid components in complex physiological matrices. The very sensitivity of most LC systems, however, which is invaluable in the analysis of biological samples, is often the limiting factor because of inadequate or ambiguous identification methods. Although tremendous advances have been made in the on-line combination of HPLC with spectroscopic techniques [e.g., mass spectrometry, Fourier transform infrared (FT/IR), nuclear magnetic resonance], their application has not become routine in most biochemical and biomedical laboratories. 

Characterization of collected fractions using spectroscopic techniques Electrochemical detection On-line mass spectrometry and IR spectroscopy Laser-induced fluorescence Photodiode array detectors Radioactivity detectors... 

Studies on complex systems, such as metalloen-zymes, increasingly require the measurement of a minor spectral component in a far larger assembly. Basic aspects of optical spectroscopic techniques that make them particularly effective are the speed, sensitivity, and linearity of light detectors as well as the intensity, stability, and precision of conventional and laser light sources. 

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