Analysis by infrared absorption

Brattain, R.R., and Beeck, Otto, Rapid precision gas analysis by infrared absorption, Bull. Am. Phys. Soc., 16, 9, 1941. 

K. F. Luft, A New Method of Analysis by Infrared Absorption. Selective Modulation, Compt, rend, 238, 1651-1653, 1954. 

Gas analysis by infrared absorption or thermal conductivity cells can also be used for the continuous measurement of the composition of the gas exiting the reactor, particularly for simple gas mixtures. Gas chromatography might be used to improve the accuracy of the gas analysis, at the expense of making the analytical procedure intermittent rather than continuous. 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

The third analysis is by infrared absorption spectrophotometry. This classical technique is often overlooked in today s mass-spectrometry dominated laboratory, but still remains a powerful tool which provides considerable information at moderate cost. Infrared spectra of the seven chromatographic fractions may be used to confirm... 

Studies of I /Ru stoichiometry previously discussed and shown in Fig. 20 suggest that these two complexes, or at least a catalyst composition of the same stoichiometry, are present during catalysis. Studies of active solutions during catalysis by high-pressure infrared spectroscopy have also confirmed the presence of these complexes (191). Under 544 atm of H2/CO at 230°C in sulfolane solvent, the infrared absorptions for the carbonyl ligands of both complexes are observed clearly. No other carbonyl absorptions are evident. Samples have also been withdrawn from catalytic reactions and cooled immediately to low temperature before analysis by infrared spectroscopy these solutions also are found to contain only [HRu3(CO)j J and [Ru(CO)3I3]. ... 

CA 47, 9207(1953)(Analysis by infrared spectroscopy of proplnrs contg various stabilizers among them Centr 2) 7)P.G.Grammacicakis, CR 248, 244-7(1959) CA 54, 8277(1960XDetn of UV absorption spectra of Centr 2) 8)Anon, "Analytical Methods for Powders and E xplosi ve s AB Bofors, Nobelkrut, Sweden(1960), 80-1 9)... 

The precision of absorbance measurements and the possibilities of storage and re-treatment of the spectra have favoured quantitative analysis by infrared. The method is widely used for the facility with which the absorption bands of a particular compound can be located even in a mixture and because efficient methods of statistical analysis are available for the near IR. However, the development of reliable ETIR instrumentation and strong computerized data-processing capabilities have greatly improved the performance of quantitative IR work. Thus,... 

The most important samples for analysis by infrared spectroscopy for crude oil chemists are organic substances. For organic molecules, the infrared spectrum can be divided into three important regions. First is the absorption of infrared radiation within the wave number range of 4000 and 1300 cm 1 which is caused by functional groups and different bond types. Second is the absorption between 1300 and 909 cm 1 that is typical for more complex interactions in the molecules. And last is the absorption between 909 and 650 cm 1, which is usually associated with the presence of aromatic compounds in the sample. 

Various forms of radiation have been used to produce ions in sufficient quantitites to yield neutral products for subsequent analysis. In principle, it should be possible to use intense beams of UV below ionization threshold for this purpose. To date, however, efforts to collect neutrals from resonant multiphoton ionization (REMPI) have not succeeded. In one experiment, 1 mbar of gaseous -propyl phenyl ether was irradiated at room temperature with a 0.1 W beam of 266 nm ultraviolet (from an 800 Hz laser that gives 8 n pulses) concurrent with a 0.5 W beam at 532 nm. The beams were intense enough not only to ionize the ether in the mass spectrometer, but also to excite it so that it expels propene. After several hours of irradiation < 10% of the starting material remained. Production of carbon monoxide and acetylene (decomposition products of the phenoxy group) could be detected by infrared absorption spectroscopy, but the yield of neutral propene (as measured by NMR spectroscopy) was infinitesimal. 

One representative method for CO2 detection is by infrared absorption analysis. An accurate measurement can be achieved by this method, but the equipment is relatively large-scale and expensive. Continuous maintenance is required to maintain calibration and precision. In addition, detection by the infrared method is not simple since practical measurements require the removal of other gases which influence the infrared absorption. 

Normally, one would not usually consider that the change from an amorphous or glassy state to a crystalline or ordered state is readily discerned by infrared absorption. With some polymers, such as polyethylene terephthalate (PET), this change in structure gives rise to diffefrences in the infrared spectrum that can be used for quantitative analysis of samples for crystalline content. With PET, a band at 10.2 was shown by Cobbs and Burton [ ] to be a function of crystallinity and variously annealed samples were run for infrared absorption and density. The density of amorphous PET is 1.33, while the density for crystalline polymer is 1.47 according to x-ray unit cell measurements. From the density-infrared absorbance samples it was then possible to construct a calibration curve of absorbance versus percent crystallinity. 

Y. Y. Mikhailenko, N. N. Lebedev, I. K. Kolchin, and E. G. Kutyrina, Analysis of Multicomponent Mixtures by Infrared Absorption Spectra. II. Determination of the Isomers of Chlo-rocumenes, ter-Butyl-chlorobenzenes, and Chlorodiphenyl-methanes, Zhur. Anal. Khim. 15, 495-499, 1960 cj. CA 54, 15088a. 

Analysis by infrared spectroscopy served only to confirm that the sample was a mixture, as the spectrum did not correspond to that of any single pure substance in the database. As organic compounds have many similar absorptions, it proved difficult to obtain a clear identification in this case. 

In general, samples to be analyzed by infrared absorption spectroscopy require adequate support (infrared cells) in such a way as to enable the acquisition of the spectrum in the apparatus. There are different types of cells, and the choice among them depends on the sample characteristics and the objective of the analysis, such as surface characterization studies or chemical reaction monitoring. ConunerciaUy available cells are of the sealed, collapsible, and variable thickness kinds, for gas, flow, high-vacuum and -pressure and micro-cells. 

The PE 2400 CHN Analyzer (Fig. 4) can be modified to perform automatic determination of oxygen. The combustion tube is filled with platinized carbon reagent. The samples are pyrolyzed in an inert atmosphere of argon or helium. The reaction product CO is separated by frontal chromatography and measured by thermal conductivity. In the Leco CHN Analyzer, carbon monoxide is converted to carbon dioxide to be measured by infrared absorption. Neither CHN method is suitable for the analysis of organic substances which contain fluorine, phosphorus, silicon, or most metallic elements. 

Lyon, R. J. P., and W. M. Tuddenham, 1960. Determination of tetrahedral aluminum in mica by infrared absorption analysis. Nature 185 374. 

Scale of Operation Molecular UV/Vis absorption is routinely used for the analysis of trace analytes in macro and meso samples. Major and minor analytes can be determined by diluting samples before analysis, and concentrating a sample may allow for the analysis of ultratrace analytes. The scale of operations for infrared absorption is generally poorer than that for UV/Vis absorption. 

The first (direct reading) method is fairly simple and results are available immediately. However, the instruments have limited sensitivity and must be recalibrated periodically. The second (absorption in a liquid or adsorption on a medium) and third (gas container) methods are generally considered more sensitive and more accurate method for trace analysis by gas chromatographs, infrared... 

---