Infrared quantitative

Daniels A., Nondestructive pulsed infrared quantitative evaluation of metals... 

Taking an example of a measurement at 5000 cm with a required resolution of 2cm but a wavenumber accuracy requirement of 0.04 cm (which are entirely typical of the requirements for a demanding near-infrared quantitative application) - the limit on is about 0.8° for the resolution, but around 0.2° for the wavenumber accuracy. 

ASTM El655-00, Standard Practice for Infrared Quantitative Analysis, ASTM International, Pennsylvania. 

ASTM E 168-92, Standard Practice for General Techniques of Infrared Quantitative Analysis, 1992. 

FIGURE 7-12 Schematic diagram and equations for infrared quantitative analysis. 

Test methods include ASTM E1252 (Standard Practice for General Techniques for Obtaining Infrared Spectra for Qualitative Analysis), ASTM El790 (Standard Practice for Near Infrared Qualitative Analysis) and ASTM El68 (Practices for General Techniques of Infrared Quantitative Analysis) (see also Chapter 7). 

Various types of low-temperature cells are available commercially. Rochkind (1968) has presented a new low-temperature (20°K) technique, which provides a practical and sensitive method of infrared quantitative analysis of all infrared-absorbing gases and volatile liquids. The method, called pseudomatrix isolation spectroscopy (PMl), also provides a tool for the analysis of complex gas mixtures. The PMI method distinguishes between molecular isotopes, for example. Figure 3.21 shows a PMl spectrum of a mixture of isotopic d2-ethylenes (condensed on a 20 K Csl window). Rochkind claims that equivalent distinguishability has not been demonstrated with gas chromatography. 

A discussion of recommended practices for general techniques of infrared quantitative analysis has been published by the American Society for Testing and Materials (1966). Perry (1970) has recently reviewed the use of infrared spectrophotometry in... 

Carbon tetrachloride is an exception and is commonly produced without a preservative. The reason for this is that carbon tetrachloride is frequently used as an aprotic solvent for infrared analyses. Infrared quantitation of oil and grease levels through the intensity of the C-H stretch can be done using carbon tetrachloride. An alkene preservative would render it unsuitable for use. 

Luty, T. and Rohleder, J.W., Near-infrared quantitative spectroscopy, Rocz. Chemi, 41,975-983,1967. 

As IR spectroscopy is a secondary method of analysis, the development of quantitative analysis methods requires calibration with a set of standards of known composition, prepared gravimetrically or analysed by a primary chemical method, to establish a relationship between IR band intensities and the compositional variable(s) of interest. The precision of the infrared quantitation cannot be better than the (instrumental) technique employed to provide the concentrations used for the calibration standards [156]. Mid-IR may be more accurate than near-IR if the solid sample presentation is correct. 

The intensities and shapes of vibrational bands are of considerable importance in spectra interpretation and infrared quantitative analysis. The intensity of an infrared band is directly proportional to the probability for the transition between the ground state and a vibrational excited state. This probability, in turn, depends primarily upon the square of the rate of change in the dipole moment for a particular vibration. An intense band indicates a large change in the dipole moment of the atoms involved during a vibration, or that many atoms or functional groups within the molecule have the same vibrational energy. 

Infrared Quantitative Analysis General Comments on Instrumental Conditions for Quantitative Analysis by Lewis E, Tufts and A bram Davis 151... 

All infrared quantitative methods measure two quantities the incident radiation — often called the 100% line — and the recorded spectrum. The various methods may be differentiated by the way in which the incident radiation is determined. 

Temperature and solvent composition control for near-infrared quantitative results... 

The accuracy of the results of infrared quantitative analysis will depend on the factors discussed in previous sections of this chapter. For a relatively ideal sample, where the operator does a careful job, the accuracy is expected to be from better than 1 % of the amount present to 3 % of the amount present, depending on the instrument used. Thus, for a research-type instrument in good operating condition, a result of 10% concentration means that the actual value is somewhere between 9.9% and 10.1 %. 

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