In addressing difficult gas measurement problems, the approach of Infrared Analysis, Inc. is to seek simplifications
We simplify quantitative sample acquisition by using syringes for capturing and diluting static samples and controlled flow with dilution for moving samples. This eliminates the need for heated absorption cells and high temperature reference spectra.
We remove water and CO2 interferences by means of spectra that are easily prepared.
We provide action buttons that prompt the computer to remove the water and CO2 lines and carry out the quantitative analysis automatically.
We have created the technique of Photolysis Assisted Pollution Analysis that in many cases will eliminate the requirement for removal of water and carbon dioxide bands.
We base our quantitative measurements only on bands with low absorbance values, where there is no deviation from the absorbance law.
Our RIAS quantitative analysis technique calls on the computer to carry out band area measurements, which the computer does much better than the operator could do in former times.
We do not try to measure everything at once. Instead, we have the computer “peel down” a complex spectrum one compound at a time, measuring concentrations as it goes.
MAIN POINTS FROM DISCUSSION IN BOOK
Here is a summary of main points that should be observed in using infrared absorption for quantitative measurements of gases.
Work in the fundamental infrared region where molecules have their strong bands.
Use high spectral resolution. (0.5 or 1.0 wavenumbers)
Use zero-filling to create well-shaped spectral lines.
Use the mercury-cadmium-telluride detector.
Use the “White” multiple-pass cell, preferably with a glass cell body.
Do not purge the spectrometer sample compartment.
Make water and carbon dioxide subtraction spectra on the same spectrometer that is used to make the sample spectra.
Use the region integration and subtraction (RIAS) method of quantitative analysis.
Do not include any bands of high absorbance in the integration region chosen for quantitative measurement.
Analyze samples at room temperature and one atmosphere total pressure.
Make proper choices of pathlength, integration region and sample dilution so that you can use a single reference spectrum in covering a concentration range of one atmosphere down to parts-per-billion.
DETAILED EXPLANATIONS OF THESE MAIN POINTS ARE GIVEN IN OUR BOOK PROCEDURES IN INFRARED ANALYSIS OF GASES.
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