"QASoft" is an automated quantitative analysis program developed by Infrared Analysis, Inc. that enables the measurement of all infrared-active gases. This program reduces the practice of gas analysis to the making of a few clicks with a mouse. Even complex mixtures of gases that have overlapping infrared spectra can be analyzed with parts-per-billion sensitivity. The program operates within GRAMS AI (vers. 5,6 or 7) (which is THERMO ELECTRON's laboratory software program) and is accessed through an Infrared Analysis, Inc. workbook. QASoft contains Spectral Libraries in two degrees of spectral resolution: 0.5 cm-1, and 1 cm-1 . These spectra permit the computation of concentrations from a sample spectrum without the need for any other calibration. The calibration is inherent in these reference spectra. In analyzing for the 392 compounds the only chemical the user will need to handle is his sample.
In "QASoft", concentration information is extracted from the spectrum by a technique known as Region Integration and Subtraction (RIAS). RIAS is an automation of the traditional method of making quantitative measurements in which areas under spectral features are calculated and compared. Band areas are compared not by the former method of hand and eye, but by the computer. The computer not only does this better than a human being, but it also removes the spectrum of the measured compound from the sample spectrum--something not previously possible. The data system will continue on through as many compounds as are designated in the program. With RIAS, one can measure any compound that has an available reference spectrum.
Air analysis presents an especially difficult problem because of the heavy burden of atmospheric water vapor. Water lines appear throughout the spectrum and even if they are fully subtracted away, they leave "dead spots" in the spectrum that can cause analytical errors. In this kind of case, RIAS is especially effective. Since RIAS can operate in narrow spectral regions, water avoidance is feasible for nearly all compounds. Each compound to be measured needs to have an integration region written into the header of the reference spectrum. The left and right sides of the integration band are specified, along with a zeroing region. The computer draws a straight zero line across the integration region, measures the y values with the reference to the zero line, and then adds them up. It does this for both sample and reference spectra. The comparison of the two integrals then gives the concentration of the gas, along with the subtraction factor that will properly remove the spectrum of the compound from the sample spectrum. The computer then carries out the subtraction. Although the integration operates only in a narrow spectral region, the subtraction removes the entire spectrum of the compound.The Instruction manual for QASoft gives a detailed discussion of the art of selecting integration and zeroing regions.
RIAS can succeed where other quantitative analysis methods will fail. RIAS can take advantage of fine structure in spectra. RIAS works best when measuring narrow spectral features--spikes(Q-branches), shoulders of bands, small bundles of lines, or even individual lines. The use of narrow spectral regions is not especially detrimental to the sensitivity of the measurements because the spectral information is concentrated in the sharp features. The use of sharp features also promotes discrimination between compounds with overlapping spectra.
"QASoft" Action Buttons
|QASoft Info||Calls up the QASoft banner showing version & registration information and a tech support contact number. [top]|
|Alph. Index||Presents an alphabetical listing of all compounds in the database, with chapter letters and molecular weights. [top]|
|Make H2O - Make CO2||These buttons prepare the H2O and CO2 subtraction spectra [top]|
|Database||Gives access to all the digitized reference spectra classified in 20 chapters according to chemical type.[top]|
|Rias Param||Permits call-up and change of the quantitative analysis parameters for any of the database spectra or other spectra the opertator may want to use for analysis.[top]|
|Measure CO2||Measures the CO2 content of a gas sample. [top]|
|Browse||Permits an operator-controlled search through the database to identify unknown lines or bands in a sample spectrum.[top]|
|Absorbance||Creates absorbance spectra from single-beam spectra while eliminating the false high absorbance values that result from noise-created negatives. [top]|
|Analyze SC||Brings up the RIAS program for measurement of the compounds in the sample, chosen one at a time.[top]|
|Analyze Seq||Brings up the RIAS program for measurement of a designated sequence of compounds.[top]||Remove H2O||Subtracts a water reference spectrum from the sample spectrum. [top]|
|Remove H2O,CO2||Removes from the sample spectrum water lines, CO2 lines and any lines of silicone vapor that may have come from vacuum grease. [top]|
|Resolution||Interchanges operations between the two available degrees of spectral resolution. [top]|
|Auto Sequence||There are three sets of Auto Sequence buttons that analyze for compounds designated by the user. For details see the topic "QASoft Action Buttons in Volme 1 of the book PROCEDURES IN INFRARED ANALYSIS OF GASES. [top]|
|AP1.....AP9||These nine buttons automatically prepare sample spectra for quantitative analysis.[top]|