Abstract:
The use of open-path Fourier transform infrared spectroscopy (OP-FTIR) to identify and quantify air emissions requires the collection of both sample and background spectra. Highly variable temporal conditions which can alter atmospheric transmission and the presence of interferants can greatly reduce the effective use of any backrground. The use of a background spectrum that is not appropriate or is not representative of the conditions in which the sample spectrum is collected can lead to improper analysis of the resulting absorbance spectra. Baseline shifts and/or changes in the shape and size of the target peaks are problems which are commonly encountered. Little data has been published that actually explores the influence of different background selection methods.
This study investigated the differences arising from the use of various background methods under controlled but rapidly changing sampling conditions. A standard shower chamber which delivered a set amount of aqueous chloroform solution was used to obtain chloroform concentrations under different temporal conditions. Mass generation values were calculated and a one way analysis of variance (ANOVE) was performed to assess statistical significance between the eight different background methods. Although statistical differences (p < .05) existed between some methods, a definite pattern between test situations was observed. Additionally, the limit of detection calculated for each OP-FTIR background method ranged over two orders of magnitude. Analysis of the shower chamber by gas chromatography also was performed but had limited comparability to the OP-FTIR background methods due to sampling point and chamber mixing differences.