QASOFT ACTION BUTTONS
MAKE H2O - MAKE CO2 These buttons prepare the H2O and CO2 subtraction spectra.
DATABASE Gives access to all the digitized reference spectra, classified in chapters according to chemical type.
RIAS PARAM Permits call-up and change of the quantitative analysis parameters for any of the database spectra.
MEASURE CO2 Measures the CO2 content of a gas sample.
BROWSE Permits an operator-controlled search through the database to identify lines or bands in a sample spectrum.
ABSORBANCE Creates an absorbance spectrum from single-beam spectra, while eliminating false high absorbance values that result from noise.
ANALYZE SC Brings up the RIAS program for measurement of compounds in a sample, chosen one at a time.
ANALYZE SEQ Brings up the RIAS program for measurement of a designated sequence of compounds, followed by print-out of the results.
REMOVE H2O Subtracts a water reference spectrum from the sample spectrum.
REMOVE H2O,CO2 Removes from the sample spectrum water lines, carbon dioxide lines and the bands of any silicone vapor that may have come from vacuum grease.
RESOLUTION Interchanges operations between the two available degrees of spectral resolution.
AUTO SEQUENCE There are three sets of Auto Sequence Buttons, which analyze for compounds designated by the user. The sequences are written into files named Autseq1.seq, Autseq2.seq and Autseq3.seq. These sequences may be written by means of the program of the above button named ANALYZE SEQ .
The buttons Spec. 1, Spec. 2, and Spec.3 activate an automatic analysis for up to 20 compounds. The analytical sequence must be written into the file Autseq1.seq. Measurement results may be printed out. Each of the three buttons runs the same analytical sequence, but each button prints the results differently. Spec. 1 prints the header information for the spectrum to which it is applied and then prints the compound names and the PPM concentrations. Spec. 2 prints only the PPM concentrations for its spectrum in a column displaced from the column of Spec. 1. Spec. 3 likewise prints PPM concentrations in a column further displaced.
The purpose of all this is to allow the printing of three sets of results side-by-side on a single page. To do this, the print-out page from Spec. 1 is fed back into the printer and then the print-out from Spec. 2 is entered on it. Then the print-out page from Spec. 2 is fed back into the printer to receive the print-out from Spec. 3. A principal application of this printing technique is to compare and average the analytical results from three separate spectra that have been recorded for a single sample. Auto Sequence Two and Auto Sequence Three operate in similar manner.
After print-out, the residual spectrum remains on the
screen for visual inspection. If other compounds are recognized, they may be
measured one at a time by means of
SC button. Also, any other analytical sequence may be run on the residual
AP1.........AP9 These nine buttons automatically prepare sample spectra for carrying out quantitative analysis. For details, see the QASoft Getting Started manual.
Part 2 of this book shows all 300 reference spectra at a resolution of 0.5 cm-1. The digitized spectra are at 0.5 cm-1 and 1.0 cm-1. Header data carried with the spectra include parameters used when doing quantitative analysis by the RIAS procedure. These are values chosen by Infrared Analysis, Inc. They may be changed by the user to suit his particular analytical problem. All digitized spectra have been doubled in size by zero-filling.
In QASoft, concentration information is extracted from the spectrum by the technique of 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 program not only does this better than a human being, but it also immediately removes the spectrum of the measured compound from the sample spectrum. THE SUBTRACTION OPERATION IS THE KEY TO THE SUCCESS OF RIAS. The data system can continue on through as many compounds as are designated in the program. With RIAS one can measure any compound that has an available digitized reference spectrum.
In air analysis, it is important to avoid regions of heavy water vapor absorption. Even though the water lines are subtracted away, some residuals will remain and noise will appear where the water absorption was intense. Since RIAS can operate in narrow spectral regions, this water avoidance is feasible for nearly all compounds. Each compound to be measured needs to have an integration region written into the header information 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 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.
RIAS can succeed where other quantitative analysis methods will fail. RIAS can take advantage of fine structure in the 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.
Here are some additional details on operation of the action buttons.
DATABASE Clicking on the database button gives immediate access to all the reference spectra. These are classified in 20 chapters, A to T, according to chemical types. Access is by chapter letter. Experience has shown that the chapter listing is more convenient for access than the alphabetical listing. If the user is not sure which chapter his compound is in, he may consult the alphabetical listing printed in the manual.
RIAS PARAM Clicking on the RIAS Parameters action button gives direct access to the header data of a reference spectrum. The analysis parameters may then be confirmed or changed. The memo may also be changed at this time, so if the analysis and zero bands are going to be altered, one may choose to write the old limits into the memo. The spectrum should first be called into the view. This may be done either with the Database button or from the QASoft directory. The click on SpecInfo then produces a query as to whether a different file is to be selected. Clicking NO then brings up the header for the spectrum in the view. Changes may then be made and stored. The new file query then reappears. Clicking on YES then brings up the Select Absorption File screen with the same directory as for the previous spectrum. When the new spectrum is selected, its header appears. Approving or changing the header returns the new file query. One may thus continue through as many headers as is desired.
BROWSE The browse function allows the user to compare an unknown spectrum--or a portion thereof--to all the spectra in the database. This is a simple type of search that may be carried out in just a few minutes. Browse may be started at the beginning of any of the 20 chapters.
ABSORBANCE The absorbance function calculates and
displays an absorbance spectrum from sample and background spectra that are
chosen by the operator. If the resultant absorbance spectrum contains the false
high absorbance values that result from negative values in the single beam
spectra, the program will eliminate those negative values and then re-calculate
and display a proper absorbance spectrum.
ANALYZE SC The analyze single component function enables the measurement of the sample spectrum for all the compounds in the database, chosen one at a time. The operator selects the compound, and the computer measures it. The computer also subtracts the complete spectrum of the compound from the sample spectrum. Stored measurement parameters may be used, or new ones may be chosen at the time of analysis. During analysis the sample spectrum, the reference spectrum and the difference spectrum are all displayed. Interactive correction of the subtraction factor is allowed. After displaying the results of the analysis, the computer asks the operator to select another compound for measurement. The program can proceed through as many compounds as are designated.
ANALYZE SEQ The analyze sequence function allows the operator to designate a series of compounds for measurement. The computer couples the measurements together in an automatic sequence. The sequence then runs, with the succession of measurements and subtractions appearing on the screen. At the end of the sequence the measurement results are printed out. The sequence may be saved and called up again whenever needed. A sequence may be run twice in succession on a single sample. In most cases the second run-through will produce all zeros as measurement values. Sometimes, however, when there are severe spectral overlaps, the first run-through will be slightly in error, and the second run-through will provide corrections. A third run-through will almost always produce zeros.