Gas analysis techniques

Two final examples of the sensitivity and general applicability of the FTIR gas analysis technique are illustrated in Fig. 8. Trace (A) shows the spectrum obtained from an ultra-air filled 70 liter sampling bag into which had been injected, 18 hours previously, 4.8 microliters of TDI, toluene diisocyanate. On the basis of the single feature at 2273 cm l, it is estimated that 50 ppb TDI could be detected. The lower Trace (B), shows the spectrum of nickel carbonyl. This highly toxic but unstable gas was found to decay rapidly at ppm concentrations in ultra air (50% lifetime 15 minutes). Calibration of its spectrum was established by recording successive spectra at ten minute intervals and by attributing the increase in carbon monoxide concentration (calibration known) to an equivalent but four times slower decrease in nickel carbonyl concentration. The spectrum shown represents 0.6 ppm of the material. Note the extraordinary absorption strength. The detection limit is thus less than 10 ppb. 

The course of combustion reactions during flammation has been studied 78) by the application of gas analysis techniques 40), by absorption spectra 76), by temperature measurements during combustion 95, 133-135), and by the analysis of indicator cards 25, 99,110.112). 

This instrument has evolved from ihe laboratory spectrophotometer to satisfy the specific needs of industrial process control. While dispersive instruments continue to be used in some applications, the workhorse infrared analyzers in process control are predominantly nondispersive infrared (NDIR) analyzers. The NDIR analyzer ean be used for either gas or liquid analysis. For simplicity, the following discussion addresses the NDIR gas analyzer, hut it should be recognized that the same measurement principle applies to liquids. The use of infrared as a gas analysis technique is certainly aided by the fact that molecules, such as nitrogen (N ) and oxygen tO , which consist of two like elements, do not absorb in the infrared spectrum. Since nitrogen and oxygen are the primary constituents of air. it is frequently possible to use air as a zero gas. 

Pongracic S., Kirschbaum M. U. F., and Raison R. J. (1997) Comparison of soda lime and infrared gas analysis techniques for in situ measurement of forest soil respiration. Can. J. Forest Res. 27(11), 1890-1895. 

One gas analysis technique using sealed adsorbent tubes borrows from the colorimetry methods of manual procedures. Draeger and now also the Gastec and the Matheson-Kitagawa systems all use glass tubes packed with a solid support which is coated with an appropriate colorimetric reagent for the gas of interest. Company literature assesses the coefficient of variation for the tubes with most readily discernable color changes as 10%, and for the less efficient tubes as 20-30% [26] (Eqs. 2.15-2.17). 

Specificity is the most important requirement in gas analysis. Techniques dependent on the physical properties of the gas molecules, such as thermal conductivity, density, viscosity, and sound velocity, generally have insufficient specificity to differentiate a single gas in a mixture of gases, and therefore must incorporate in the procedure some type of preliminary separation. Vapor phase fractionation (gas chromatography) is an example of a popular analytical technique based upon a physical property (thermal conductivity) of the gas that requires preliminary separation of the gases by means of special columns (molecular sieve, silica gel, etc.). 

The first quantitative results for the decomposition of starch into carbon monoxide, carbon dioxide, and water are those of Puddington. He showed that pyrolysis of starch is more rapid under vacuum than at atmospheric pressure, that is, that the reaction probably does not involve oxidation. Puddington made a kinetic study of the decomposition of potato starch, in the narrow temperature range of 180-210°, at 10 mm. A conventional, vacuum line of glass permitted the pyrolysis products to be trapped or collected. The amounts of carbon monoxide, carbon dioxide, and water were determined by classical, gas-analysis techniques. 

Precise gas analysis technique is essential in order to obtain compositional analysis data for the reliable determination of natural gas heating values. Since 1977, laboratories in Indonesia and Japan serving the LNG export and import trade between these countries have co-operated to develope analytical procedures, based on GPA Standard 2261, that provide the required level of reliability. This paper sets out to show that stringent adherence to technique together with carefull selection of equipment and reference materials can achieve the level of rehability required to accurately calculate LNG heating value. 

Barnes [24] showed that evolved gas analysis techniques when linked to mass spectrometry are very useful for determining residual volatile additive and/or their degradation products. 

Kane, R. H. and GoodeU, P. D., Gas Analysis Techniques for High Temperatture Corrosion Testing, Journal of Testing and Evaluation, November 1982, pp. 286-291. 

Evolved gas analysis techniques have recently been reviewed [922]. 

H. Mohler, H. Walter and S. Knappe, in Coupling of Themud Analysis and Gas Analysis Techniques and Applications (E. Kaisersberger, E. Kapsch,... 

This equation has traditionally been used to calculate CE, with the use of various gas analysis techniques to determine the concentrations of C02(g) and CO(g) in the anode gas. Thus, measurement of the C02(g)/C0(g) ratios gives an instantaneuos CE determination. Prediction of CE by this equation is usually believed to be accurate within a few percent. Error limits are discussed in [1], and these are mainly due to difficulties in determining the exact extent of side reactions like the reaction between carbon, oxygen, and CO2, the electrolytic formation of CO, the back reduction of CO, the oxidation of aluminum carbide, the effect of sulfurous gases, and so on. 

Topical issues on the advantages and limitations of TG-MS with respect to other evolved gas analysis techniques have recently been summarised by Raemaekers and Bart a.l0] in a review on TG-MS thermal degradation of polymers. The advantageous applications of the technique in polymer science can be extended from qualitative thermal degradation analyses to thermooxidation, structural characterisation and chemical analyses, kinetics, solid-state reaction mechanisms, chemical reactivity and curing, quantitative analyses, and finally product formulation and development. 

Attempts have been made to apply an evolved gas analysis technique (EGA) to investigate cement systems. In the EGA technique, a... 

Analysis of fermentations by the unit-operation technique has added greatly to the understanding of their behavior. This understanding, however, is far from complete. The scale-up of fermentations for instance, is still rather empirical although the sensitive oxygen probes and sensitive gas analysis techniques now available have enabled a more rational approach to scaling-up aerated, non-newtonian fermentations. 

Fig. 7.12 Schematic representation of the calorimeter coupled with a manometric device and a gas analysis technique used to study the coadsorption of gas. Details of the connection of the six-way valve used for GPC or MS sampling...

As a means of monitoring gas compositions, some independent verification of the performance of PTR-MS would help to build confidence in the technique. Such verification smdies have been carried out and involve comparisons with other gas analysis techniques, particularly gas chromatography (GC). It is important to recognize at the outset that PTR-MS and GC techniques will not always agree, since PTR-MS using a mass spectrometer may not be able to separate compounds with the same nominal mass, whereas GC-MS almost always can because of the additional discrimination provided by compound separation on the chromatographic column. An additional complication is that fragment ions from... 

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