Completely automated open-path FT-IR spectrometry

Griffiths, P.R. and Shao, L. and Leytem, A.B. (2009) Completely automated open-path FT-IR spectrometry. Analytical and Bioanalytical Chemistry. 393(1):45-50.

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Abstract

Atmospheric analysis by open-path Fourier-transform
infrared (OP/FT-IR) spectrometry has been
possible for over two decades but has not been widely
used because of the limitations of the software of commercial
instruments. In this paper, we describe the current state-of-
the-art of the hardware and software that constitutes a
contemporary OP/FT-IR spectrometer. We then describe
advances that have been made in our laboratory that have
enabled many of the limitations of this type of instrument to
be overcome. These include not having to acquire a single-beam
background spectrum that compensates for absorption
features in the spectra of atmospheric water vapor and carbon
dioxide. Instead, an easily measured “short path-length”
background spectrum is used for calculation of each
absorbance spectrum that is measured over a long pathlength.
To accomplish this goal, the algorithm used to
calculate the concentrations of trace atmospheric molecules
was changed from classical least-squares regression (CLS)
to partial least-squares regression (PLS). For calibration,
OP/FT-IR spectra are measured in pristine air over a wide
variety of path-lengths, temperatures, and humidities,
ratioed against a short-path background, and converted to
absorbance; the reference spectrum of each analyte is then
multiplied by randomly selected coefficients and added to
these background spectra. Automatic baseline correction for
small molecules with resolved rotational fine structure, such
as ammonia and methane, is effected using wavelet transforms.
A novel method of correcting for the effect of the
nonlinear response of mercury cadmium telluride detectors
is also incorporated. Finally, target factor analysis may be
used to detect the onset of a given pollutant when its
concentration exceeds a certain threshold. In this way, the
concentration of atmospheric species has been obtained
from OP/FT-IR spectra measured at intervals of 1 min over a
period of many hours with no operator intervention.

Item Type:	Article
NWISRL Publication Number:	1281
Subjects:	Manure
Depositing User:	Users 6 not found.
Date Deposited:	18 Dec 2008 22:05
Last Modified:	18 Oct 2016 15:21
Item ID:	1304
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/1304