Evaluating open-path FTIR spectrometer data using different quantification methods libraries and background spectra obtained under varying environmental conditions

摘要

This paper discussed studies performed in a 35 foot outdoor Teflon exposure chamber in Pittsboro, North Carolina. The purpose of this research was to evaluate open-path FTIR data and compare it to a reference method varying several parameters: the method used for quantification, the library used for quantification, and backgrounds representing varying environmental conditions. The reference method used was GC-FID. The chemical evaluated was toluene over the concentration range of 5-30 ppm. Two different quantification methods were used in this analysis: traditional peak area method and interactive subtraction. All quantification was done manually. Two different libraries were used for quantification: the Hanst library (137 ppm-m toluene) and the EPA library (249 ppm-m) toluene. Several concentration data files were analyzed with the original background and then with subsequent backgrounds obtained from that same day. The subsequent backgrounds contained varying amounts of water vapor. The effect on quantification was evaluated. For concentrations of 20 ppm and below there was no significant difference between the peak area and subtraction method. However, for concentrations greater than 20 ppm, the difference between the two methods increased up to 20%. The difference between the EPA and Hanst libraries was statistically insignificant below 25 ppm. At concentrations greater than 15 ppm, the two libraries deviated and the difference ranged from 5% to 10% with the EPA results being higher. Water vapor was found to drastically impact the quantification. The magnitude of the effect varied between quantification methods and libraries.