The NIST quantitative infrared database

Abstract

With the recent developments in Fourier transform infrared (FTIR) spectrometers it is becoming more feasible to place these instruments in field environments. As a result, there has been enormous increase in the use of FTIR techniques for a variety of qualitative and quantitative chemical measurements. These methods offer the possibility of fully automated real-time quantitation of many analytes; therefore FTIR has great potential as an analytical tool. Recently, the U.S. Environmental Protection Agency (U.S.EPA) has developed protocol methods for emissions monitoring using both extractive and open-path FTIR measurements. Depending upon the analyte, the experimental conditions and the analyte matrix, approximately 100 of the hazardous air pollutants (HAPs) listed in the 1990 U.S.EPA Clean Air Act amendment (CAAA) can be measured. The National Institute of Standards and Technology (NIST) has initiated a program to provide quality-assured infrared absorption coefficient data based on NIST prepared primary gas standards. Currently, absorption coefficient data has been acquired for approximately 20 of the HAPs. For each compound, the absorption coefficient spectrum was calculated using nine transmittance spectra at 0.12 cm−1 resolution and the Beer’s law relationship. The uncertainties in the absorption coefficient data were estimated from the linear regressions of the transmittance data and considerations of other error sources such as the nonlinear detector response. For absorption coefficient values greater than 1 × 10−4 μmol/mol)−1 m−1 the average relative expanded uncertainty is 2.2 %. This quantitative infrared database is currently an ongoing project at NIST. Additional spectra will be added to the database as they are acquired. Our current plans include continued data acquisition of the compounds listed in the CAAA, as well as the compounds that contribute to global warming and ozone depletion.

Improved mid-infrared cross-sections for peroxyacetyl nitrate (PAN) vapour

“…3). As PAN absorption bands do not approach saturation in these measurements, this error weighting method was considered to be more reliable in calculating such fits to Beer's law, rather than using the transmission weighting approach described by Chu et al (1999) for bands that approach saturation. Figure 1 shows peak absorbances measured for each of the five principal PAN bands plotted against determined PAN partial pressure.…”

Retrieval of sulfur dioxide from a ground-based thermal infrared imaging camera

“…The filter response function is plotted in Fig. 5 together with the SO 2 absorption coefficient measured by NIST (National Institute of Standards and Technology) (Chu et al, 1999).…”

Feasibility Study of Using Short Wave Infrared Cavity Ringdown Spectroscopy (SWIR-CRDS) for Biological Agent Detection

“…This multiple burden method greatly improves the S/N ratio by using the high burden measurements to enhance the signal for the weak bands that might not exceed the noise floor in any given measurement (while down-weighting the nonlinear strong peaks), but also using the low burden measurements to bring out a better fidelity for the strong peaks by accounting for Beer's law saturation and detector nonlinearity effects. Chu et al 51 and Sharpe et al 52 have demonstrated the advantages of this method compared to a simple linear absorbance data fit at each wavelength bin, since the raw data also have a weighting factor to account for nonlinearity mechanisms. In this method the residual fit vector is, moreover, carefully analyzed since any chemical impurities, including the uncommon ones, readily manifest themselves in the fit residual.…”

“…Quantitative near-infrared cross-sections were determined using a slight variant of the method of Chu et al 50 and Sharpe et al 51 In this method, a series of Fourier transform IR measurements is made, each corresponding to a different mixing ratio of the pure analyte vapor in a stream of ultra-high purity (UHP) nitrogen gas. After the measurements, a composite absorption spectrum A(λ) is generated from the individual spectrum; the individual (298.1 K) measurements cover a large range (~2 orders of magnitude) of analyte burdens, each burden pressurized with N 2 to one atmosphere.…”