CONCENTRATION RANGE FOR QUANTITATIVE ANALYSIS
Our software, QASoft, allows quantitative measurement of gases at partial pressures from one atmosphere down to one billionth of an atmosphere, or lower. In other words, the measurable concentrations span 9 orders of magnitude. This is done with one reference spectrum per compound, while working with the requisite low absorbances.
Here we list the ways in which the 9 decades of concentration are accessed.
1. Have a spectrum noise level no higher than 0.0001 absorbance units (base 10). This will allow strong spectral features to be used for quantitative analysis from 0.0001 absorbance units up to 0.1 absorbance units. Thus, 3 decades of concentration are covered in one measurement.
2. Change the path length of the absorption cell. Gas cells are obtainable with optical paths from one millimeter to one hundred meters. These pathlength changes can therefore move the three decade measurement region over a five decade span.
3. To go up in concentration, switch the integration from strong spectral features to weak spectral features. In many cases, one can find a good spectral region 100 times weaker than the main spectral features. The shift will move the three decades of measurement up two more decades.
4. To go up farther, dilute the sample with optically transparent gas, such as nitrogen. On the matter of dilution, see also the discussion under the topic ROOM TEMPERATURE WORK, BENEFITS OF AND TECHNIQUES FOR.