Spectroscopy multiple wavelength

Since modern FTIR spectrometers can operate in a rapid scan mode with approximately 50 ms time resolution, TRIR experiments in the millisecond time regime are readily available. Recent advances in ultra-rapid scanning FTIR spectroscopy have improved the obtainable time resolution to 5 ms. Alternatively, experiments can be performed at time resolutions on the order of 1-10 ms with the planar array IR technique, which utilizes a spectrograph for wavelength dispersion and an IR focal plane detector for simultaneous detection of multiple wavelengths. ... 

Infrared (IR) spectroscopy offers many unique advantages for measurements within an industrial environment, whether they are for environmental or for production-based applications. Historically, the technique has been used for a broad range of applications ranging from the composition of gas and/or liquid mixtures to the analysis of trace components for gas purity or environmental analysis. The instrumentation used ranges in complexity from simple filter-based photometers to optomechanically complicated devices, such as Fourier transform infrared (FTIR) spectrometers. Simple nondispersive infrared (NDIR) insttuments are in common use for measurements that feature well-defined methods of analysis, such as the analysis of combustion gases for carbon oxides and hydrocarbons. For more complex measurements it is normally necessary to obtain a greater amount of spectral information, and so either Ml-spectrum or multiple wavelength analyzers are required. 

Diffuse reflectance differs from classical transmission in which no particulate matter exists to scatter the beam of radiation. It is necessary to contrast correlation spectroscopy (correlation analytical techniques based on spectroscopic measurements) to a classical, one wavelength, monochromatic application of Beer s law. The use of multiple wavelengths produces a multiterm analytical equation in reflectance R of the general type ... 

The most commonly-used detectors are those based on spectrophotometry in the region 184-400nm, visible ultraviolet spectroscopy in the region 185-900nm, post-column derivativisation with fluorescence detection (see below), conductivity and those based on the relatively new technique of multiple wavelength ultraviolet detectors using a diode array system detector (described below). Other types of detectors available are those based on electrochemical principles, refractive index, differential viscosity and mass detection. 

For all types of chemical analysis, the quality of the results ultimately relates to the chemical purity of the best available SRM. For naturally chiral substances, there is the additional more serious concern over what constitutes absolute enantiomeric purity. Not even mass spectroscopy, which provides assurance that a substance is chemically pure, can be used to report absolute enantiomeric purities. To actually report an enantiomeric purity higher than 99% is truly beyond the capability of current analytical methodology. ° As noted previously, the fact is that results are measured relative to an enantiopurity defined to be 100%. Chemical purities aside, the measurement of enantiomeric purity and enantiomeric excess is technically the same, the difference being the extent of race-mization. There are only two experimental options, either enantiomeric separations or multivariate spectroscopic analyses, that involve either two distinct detectors or multiple-wavelength detection for a single detector, as noted above. The newly described derivati-zation reactions fulfill the second option. 

NIR spectroscopy became much more useful when the principle of multiple-wavelength spectroscopy was combined with the deconvolution methods of factor and principal component analysis. In typical applications, partial least squares regression is used to model the relation between composition and the NIR spectra of an appropriately chosen series of calibration samples, and an optimal model is ultimately chosen by a procedure of cross-testing. The performance of the optimal model is then evaluated using the normal analytical performance parameters of accuracy, precision, and linearity. Since its inception, NIR spectroscopy has been viewed primarily as a technique of quantitative analysis and has found major use in the determination of water in many pharmaceutical materials. 

Over the past decade, there has been considerable development in imaging type detectors for the measurement of ultraviolet (UV) and visible light. These new detectors have attracted the interest of a number of analytical spectroscopists. For absorption spectroscopy, analytical chemists have traditionally used such instruments as the photometer, which uses a narrow-band light source (for example the 254 nm emission line from a low pressure Hg lamp or a continuous source with a filter), a sample cell and a photomultiplier tube (FMT) as the detector. While useful for many specific applications, the single-wavelength photometer cannot determine multiple sample components simultaneously or provide a general absorbance characterization of the system. When information at multiple wavelengths is desired,... 

Hyperspectral imaging (HSl) combines spectroscopy and the traditional imaging to form a three-dimensional structure of multivariate data (hypercube). The hyperspectral images are consist of many spectral bands acquired in a narrow and contiguous way, allowing to analyze each pixel in the multiple wavelengths simultaneously and, therefore, to obtain a... 

Classical spectroscopy requires physical separation of the constituent of interest from the matrix, usually by dissolution in a solvent. When considering vibrational spectroscopic analysers, a major component will have numerous wavelengths at which it may be analysed. Minor components require the analyst to seek wavelengths at which they have major absorbances and, almost invariably, use multiple wavelength correlation techniques. In an ideal Beer s law calibration, the matrix is nonabsorbing (and non-scattering) and does not interact with the analyte. This is rare in industrial practice. Usually, the matrix will be a major consideration in how analysis is to be performed. By applying chemometric principles to NIR spectra, the absorption band due to the constituent of interest... 

Fundamental Physical Applications of Laser Spectroscopy. - Multiple Photon Dissociation. -New Sub-E)oppler Interaction Techniques. - Highly Excited States, Ionization, and High Intensity Interactions. - Optical Transients. - High Resolutionand Double Resonance. - Laser Spectroscopic Applications. - Laser Sources. - Laser Wavelength Measurements. - Postdeadline Papers. 

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