Infrared spectrometry instrument

With recent developments in analytical instrumentation these criteria are being increasingly fulfilled by physicochemical spectroscopic approaches, often referred to as whole-organism fingerprinting methods.910 Such methods involve the concurrent measurement of large numbers of spectral characters that together reflect the overall cell composition. Examples of the most popular methods used in the 20th century include pyrolysis mass spectrometry (PyMS),11,12 Fourier transform-infrared spectrometry (FT-IR), and UV resonance Raman spectroscopy.16,17 The PyMS technique... 

The identification of GC peaks other than through retention data, which are sometimes ambiguous or inconclusive, can be facilitated by the direct interfacing of GC with infrared spectrometry (p. 378 et seq.) or mass spectrometry (p. 426 etseq.), so-called coupled or hyphenated techniques. The general instrumental arrangement is shown in Figure 4.29(a). 

The unique appearance of an infrared spectrum has resulted in the extensive use of infrared spectrometry to characterize such materials as natural products, polymers, detergents, lubricants, fats and resins. It is of particular value to the petroleum and polymer industries, to drug manufacturers and to producers of organic chemicals. Quantitative applications include the quality control of additives in fuel and lubricant blends and to assess the extent of chemical changes in various products due to ageing and use. Non-dispersive infrared analysers are used to monitor gas streams in industrial processes and atmospheric pollution. The instruments are generally portable and robust, consisting only of a radiation source, reference and sample cells and a detector filled with the gas which is to be monitored. 

The technique is currently not used as widely as UV, visible and infrared spectrometry partly due to the high cost of instrumentation. However, it is a powerful technique for the characterization of a wide range of natural products, raw materials, intermediates and manufactured items especially if used in conjunction with other spectrometric methods. Its ability to identify major molecular structural features is useful in following synthetic routes and to help establish the nature of competitive products, especially for manufacturers of polymers, paints, organic chemicals and pharmaceuticals. An important clinical application is NMR imaging where a three-dimensional picture of the whole or parts of a patient s body can be built up through the accumulation of proton spectra recorded over many different angles. The technique involves costly instrumentation but is preferable to... 

In order to perform qualitative and quantitative analysis of the column effluent, a detector is required. Since the column effluent is often very low mass (ng) and is moving at high velocity (50-100 cm/s for capillary columns), the detector must be highly sensitive and have a fast response time. In the development of GC, these requirements meant that detectors were custom-built they are not generally used in other analytical instruments, except for spectroscopic detectors such as mass and infrared spectrometry. The most common detectors are flame ionization, which is sensitive to carbon-containing compounds and thermal conductivity which is universal. Among spectroscopic detectors, mass spectrometry is by far the most common. 

The methodology that involves instruments that utilize the interferometer and Fourier transformation mentioned in Section 8.6 has come to be known as Fourier transform infrared spectrometry (FTIR). 

NMR spectrum. Fourier transform nuclear magnetic resonance (FTNMR) instruments, which are similar in principle to Fourier transform infrared spectrometry (FTIR) instruments, are popular today. We will briefly describe these instruments later in this section. 

Ref. Griffiths, P. R., Fourier Transform Infrared Spectrometry Theory and Instrumentation , in Transform Techniques in Chemistry, P.R. Griffiths, ed., Plenum Press, New York (1978) p. 125... 

The second most used instrumental technique is that of infrared spectrometry. In general the first instrumental method to consider is the one most readily available. In a few cases, notably mass spectrometry, the technique may be used in tandem with the gas chromatograph, but most techniques require trapping of the peaks as discussed in Section 4.2.3. 

Data Analysis. The computerization of spectrometers and the concomitant digitization of spectra have caused an explosive increase in the use of advanced spectmm analysis techniques. Data analysis in infrared spectrometry is a very active research area and software producers are constandy releasing more sophisticated algorithms. Each instrument maker has adopted an independent format for spectmm files, which has created difficulties in transferring data. The Joint Committee on Atomic and Molecular Physical Data has developed a universal format for infrared spectmm files called JCAMP-DX (52). Most instrument makers incorporate in their software a routine for translating their spectmm files to JCAMP-DX format. 

Since 1905, when William W. Coblentz obtained the first infrared spectrum (1), vibrational spectroscopy has become an important analytical tool in research and in technical fields. In the late 1960s, infrared spectrometry was generally believed to be an instrumental technique of declining popularity that was gradually being superseded by nuclear magnetic resonance (NMR) and mass spectrometry (MS) for structural determinations and by gas and liquid chromatography for quantitative analysis. 

For maximum benefit, testing must be conducted rapidly and for this reason many oil companies have developed proprietary and automated test methods for routine oil analysis. The methods are cross-referenced to standard methods and utilise modern analytical instruments. For example, the standard method for determining the water content of a lubricating oil sample is distillation but various proprietary methods have been developed based on the use of gas chromatography, near-infrared spectrometry and vapour pressure. 

Infrared spectrometry Rotatory dispersion early 1950 s 1955 Commercial instrument... 

Gas chromatography (GC) has already been described and is an excellent separation technique for compounds that are volatile, thermally stable, generally of small molecular weight and nonpolar in nature. The common detectors for GC are the FID, NPD, ECD, TCD and FPD, all of which have been discussed in Section 3.1 (Figure 3.36). However, sometimes it is desirable to have a more powerful detector attached to a GC instrument and, as such, the following combinations are possible GC-infrared spectrometry, GC-mass spectrometry and even GC-infrared-mass spectrometry. Further information on GC tandem techniques can be found elsewhere. ... 

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