Page:NIOSH Manual of Analytical Methods - 3800.pdf/32

ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 32 of 47 One technique to check for the linearity of this set is to form a normalized average of these five spectra and then use it in a linear analysis of the five original spectra. The normalization consists of dividing each spectrum by its concentration-pathlength product; these values, based on the CTS-derived pathlength of 10.23 meters, are given with the actual gas concentrations and new spectral filenames in Table D3. Figure D2 illustrates the normalized spectra, all of which represent spectra of concentration-product values 1.00 ppm-meters. These spectra are nearly equal to one another, as predicted by Beer’s Law. Only the spectrum tfe01n.spc, based on the original 25.53 ppm spectrum, is easily discernable from the other spectra in the Figure.

NIOSH Manual of Analytical Methods, Fourth Edition