Infrared spectrometer sampling techniques

Vibrational spectra were recorded using the polarization-modulated infrared reflection absorbance technique (PM-IRRAS). The spectrometer, the electrochemical cell, and the sample preparation and cleaning procedures are all described elsewhere (1 7) All of the measurements were performed using 0.5 M SO solutions, either with or without an added nitrile compound or SnCl,. The solutions were saturated with CO by bubbling the gas through their storage reservoirs before admitting them into the sample cell. 

To record the infrared spectra, samples of the parent kaolinite and the three hydrates were dispersed in a fluorinated hydrocarbon. The mulls were squeezed between calcium fluoride plates and the sample was placed directly in the beam of a Perkin-Elmer 683 spectrometer. This mounting technique results in a tendency for the clay layers to align themselves perpendicular to the beam of the spectrometer. Infrared spectra of these materials have been pub-... 

Infrared spectroscopy has proven to be a very informative and powerful technique for the characterization of zeolitic materials. Most infrared spectrometers measure the absorption of radiation in the mid-infrared region of the electromagnetic spectrum (4000-400 cm or 2.5-25 xm). In this region of the spectrum, absorption is due to various vibrational modes in the sample. Analysis of these vibrational absorption bands provides information about the chemical species present. This includes information about the structure of the zeolite as well as other functional... 

Braden B, Haisch M, Duan LP et al (1994) Clinically feasible stable-isotope technique at a reasonable price - analysis of 13C02/12C02-abundance in breath samples with a new isotope selective nondispersive infrared spectrometer. Zeitschrift fur Gastroenterologie 32(12) 675-678... 

It appears there would be several advantages in using the proposed infrared method analyses could be performed much faster using the IR method. An IR scan takes 45 seconds versus -16 minutes by the NI0SH GC method. The IR method is adapted to charcoal tubes sampled by current recommended techniques. The majority of laboratories have infrared spectrometers and the simplest of models will do utilization of the IR method would relieve pressure of the heavily used gas chromatographs. The... 

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

As with optical spectroscopy, the Raman effect can be applied non-invasively in a wide range of environments. In contrast with infrared spectroscopy, Raman measurements do not require complicated sampling techniques. In addition, optical fiber probes can be used for bringing the laser light to the sample and transporting scattered light to the spectrometer, thus allowing remote detection of Raman spectra. 

Conventional Raman spectroscopy cannot be applied directly to aqueous extracts of sediments and soils, although it is occasionally used to provide information on organic solvent extracts of such samples. Fourier transform Raman spectroscopy, on the other hand, can be directly applied to water samples. The technique complements infrared spectroscopy in that some functional groups, eg unsaturation, give a much stronger response in the infrared. Several manufacturers (Perkin-Elmer, Digilab, Broker) now supply Fourier transform infrared spectrometers. 

Future spacecraft missions to solar system objects are primarily being oriented towards remote-sensing experiments, in contrast to the soft-landed in situ experiments and sample-return initiatives during the 1970 s and 1980 s. Because reflectance spectroscopy has become one of the most important investigative techniques in the planetary sciences, current and planned space missions for the 1990 s and 21st century should include visible and near-infrared spectrometers in their instrument payloads. Reflectance spectral measurements from space would provide more favourable viewing geometries, eliminate problems due to telluric water and C02, and improve the resolution of areas scanned on a nearby planetary surface. 

Infrared transmission spectra of the solid samples were measured by the KBr wafer technique. Spectra were recorded on a Perkin-Elmer infrared spectrometer, model 580 B. 

With the continuous improvement of sampling techniques, software, and instrumental designs, more and moresophisticated FTIR spectrometers are now available. Analytical Chemistry biannually reviews the most recent developments in many fields of analytical techniques, including infrared spectroscopy, many times on a yearly basis. 

There are two generally applicable methods of preparing dried humic samples for IR spectroscopy—the alkali halide pressed-pellet method and the r-ull technique. In the pressed-pellet method approximately 1 mg of the cned sample is thoroughly mixed with about 100 mg of dried alkali halide s.ili. usually KBr, and compressed into a pellet which is then placed in the s.i.Tiple path of an infrared spectrometer and its spectrum recorded. As KBr -s infrared-transparent over the conventional range of 4000 to 400 cm only -.e spectrum of the sample within the KBr matrix is observed. This proce-cjre. with its advantages and limitations, is discussed further in the follow-.-.g references (Stimson, 1962 Fridman, 1967 Parker, 1971 Price, 1972 Ataman and Mark, 1976). 

I suggest the use of infrared spectroscopy for the laboratory tests. Samples of the him can be mounted in the path of the infrared light beam in an infrared spectrometer and the resulting infrared transmission spectra recorded. If your staff is not familiar with infrared spectroscopy or the interpretation of infrared transmission spectra, you might allow them some time to read some basic reference material on this technique. I can provide that for you. The transmission spectrum recorded by the spectrometer is like a fingerprint of the material in the path of the light. It is a pattern that is observed each time that material is tested. 

It can be seen that the concentration of the substance in the sample can be calculated by comparing the input and output intensity of the infrared radiation. However, the input intensity is actually not a constant value. It varies depending on the frequency or wave number of infrared radiation. This means that the initial intensity of infrared radiation must be measured for every frequency before analyzing the sample. However, this problem is solved in modem infrared spectrometers by using a double beam technique. In this method, the beam of infrared... 

Infrared spectroscopic techniques have long been used to analyze gas streams in industrial chemical processes. Recently, with the advent of fastscan infrared spectrometers, they have been used as gas chromatograph detectors. One requirement of their use, needless to say, is that the compound must possess one or more infrared absorption band. By means of a carrier gas. the evolved gas sample from a pyrolysis chamber can be readily passed through an infrared cell for analysis. Infrared systems that can be employed include (1) nondispersive analyzers, (2) dispersion spectrometers. 3) band-pass filter-type instruments, and (4) interference spectrometers all these techniques have been adequately reviewed by Low (87). 

Many analytical laboratories are equipped with an infrared spectrometer, be it an older-style dispersive machine or a more modern Fourier-transform instrument. The results obtained from this particular technique are typically used in conjunction with the information gained from a variety of other analytical methods, such as nuclear magnetic resonance spectroscopy, mass spectrometry, ultraviolet-visible spectroscopy, or chromatography, in order to obtain information abbut a wide range of samples. 

The operation of dispersive instruments is generally straightforward, with most of j he skill involved being associated with the sample preparation. If you have access to a Fourier-transform infrared spectrometer, you will probably need to spend some time becoming familiar with the computer software which drives the instrument. Some suggestions for experiments to try out yourself are listed here. However, it is not necessary to attempt all of those mentioned. You may decide to concentrate on samples and sampling techniques which are relevant to your field of interest. 

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