Infrared disadvantages

FTIR also has several disadvantages. For example, depth profiling is not possible in RAIR. In ATR, surfaee sensitivity is limited to approximately the wavelength of infrared radiation or about one micrometer (see below). The spatial resolution of eonventional infrared teehniques is limited by diffraetion effeets and is only approximately a few tens of micrometers. 

The noncontact measurement principle, usually called optical or radiation temperature measurement, is based on detecting electromagnetic radiation emitted from an object. In ventilation applications this method of measurement is used to determine surface temperatures in the infrared region. The advantage is that the measurement can be carried out from a distance, without contact with the surface, which possibly influences the heat balance and the temperatures. The disadvantages are that neither air (or other fluid) temperature nor internal temperature of a material can be measured. Also the temper-... 

In general, physical methods have been used to study tautomerism more successfully than chemical methods, and, of the physical methods, those involving measurements of basicities and ultraviolet spectra are the most important, followed by those involving measurement of infrared and proton resonance spectra. An attempt is made here to delineate the scope and to indicate the advantages and disadvantages of the various methods. A short review by Mason of the application of spectroscopic methods appeared in 1955. Recently a set of reviews on the applications of physical methods to heterocyclic chemistry has appeared, which treats incidentally the determination of tautomeric structure. 

The most widely used techniques for surface analysis are Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), Raman and infrared spectroscopy, and contact angle measurement. Some of these techniques have the ability to determine the composition of the outermost atomic layers, although each technique possesses its own special advantages and disadvantages. 

Traditional infrared spectrophotometers were constructed with mono-chromation being carried out using sodium chloride or potassium bromide prisms, but these had the disadvantage that the prisms are hygroscopic and the middle-infrared region normally necessitated the use of two different prisms in order to obtain adequate dispersion over the whole range. 

Whilst nothing can improve upon the disadvantage of low molar absorption coefficients, instrumental designs and improvements with ratio recording and FT-IR instruments have virtually overcome the accuracy and instrumental limitations referred to in (b) and (c) above. As a result, quantitative infrared procedures are now much more widely used and are frequently applied in quality control and materials investigations. Applications fall into several distinct groups ... 

Semiconductors. In Sections 2.4.1, 4.5 and 5.10.4 basic physical and electrochemical properties of semiconductors are discussed so that the present paragraph only deals with practically important electrode materials. The most common semiconductors are Si, Ge, CdS, and GaAs. They can be doped to p- or n-state, and used as electrodes for various electrochemical and photoelectrochemical studies. Germanium has also found application as an infrared transparent electrode for the in situ infrared spectroelectrochemistry, where it is used either pure or coated with thin transparent films of Au or C (Section 5.5.6). The common disadvantage of Ge and other semiconductors mentioned is their relatively high chemical reactivity, which causes the practical electrodes to be almost always covered with an oxide (hydrated oxide) film. 

Infrared Spectroscopy. The use of IR (9.10.11.12) and FTIR (3.4) for coal mineralogy has been reported. Painter and coworkers (3) demonstrated that FTIR can provide a virtually complete analysis. Painter, Brown and Elliott (4), and others (9.10.11) discuss sample preparation, reference minerals, and data analysis. The advantages of IR are 1) high sensitivity to molecular structure, 2) unequivocal identification of a number of minerals, 3) small sample size (a few milligrams), and 4) rapid analysis time (once LTA is available). Disadvantages include 1) reliance on reference minerals, 2) requires careful attention to sample preparation, and 3) limited selectivity (discrimination among similar minerals). 

---