Quantitative gas chromatography/Fourier transform infrared spectrometry with integrated gram-Schmidt reconstruction intensities

Abstract

An Interferogram-based callbratlon curve approach to quantltatlve GCIFTIR using Integrated Gram-Schmidt reconstructlon lntensltles Is presented. The expected quantltatlve response Is derived from theory and supported wlth emplrlcal evidence. Accurate on-the-fly quantltatlon Is demonstrated over a concentration range correspondlng to absolute analyte amounts ranging from 1 pg to greater than 100 pg using pentyl propionate as the analyte.The combination of the separation ability of a gas chromatograph with the identification ability of an infrared spectrometer (GCIR) became practical with the introduction of rapid scanning Fourier transform infrared (FTIR) spectrometers in the 1960s. Subsequent development in the early 1970s has made GC/FTIR useful for a variety of qualitative applications which have been reviewed by Erikson ( I ) . The quantitative capabilities of the technique, however, have been little explored to date.The myriad difficulties associated with any attempt at absolute quantitation using FTIR have been outlined by Hirschfeld (2). Anderson and Julian have proposed using library absorptivity values for rough (=t25%) absolute quantitation of GC/FTIR data (3). While the dramatic improvement in spectral accuracy obtainable with Fourier transform instruments offers hope for the future development of accurate absolute quantitative methodology, researchers are currently limited to a calibration curve approach for handling the effects of large interlaboratory variance in instrumental and mathematical operating parameters. Erikson used a calibration curve approach for quantifying carbonyl sulfide and ammonia concentrations in coal gas, using one analytical wavelength for each component (4). Mamantov and co-workers also used a single wavelength calibration curve approach for quantifying matrix isolation GC/FTIR data (5). Greater sensitivity in quantitative trace gas analysis was demonstrated by Haaland, who used a least-squares approach employing the entire IR spectral range (6).The quantitative on-the-fly detection of GC/FTIR eluents involves several additional considerations. Upon exit from the chromatograph, absorbing species are in the vapor state diluted by a substantial volume of inert carrier gas. The variance of absorptivity with concentration due to intermolecular bonding effects (7) is thus minimized, extending the linear range of absorbance vs. concentration profiles. However, several complicating factors arise at the interface between the chromatograph and the spectrometer. The effective pathlength of the light pipe interface as it relates to factors such as the temperature and reflectivity of the gold surface in the light pipe must be determined to allow absolute quantitation using measured absorptivities (3). Additionally, the light pipe Foxboro Analytical, 140 Water St., P.O.B. 5449, Norwalk, CT 06856.can hardly be considered a zero dead volume chromatographic detector. The quantitative GCIR response must therefore be corrected for the effects of flow rate and light pipe volume. On the other han...

Gram—Schmidt Orthogonalization for Rapid Reconstructions of Fourier Transform Infrared Spectroscopic Imaging Data

“…10 In particular, the size and position of this window may be critical to the predictive performance of the technique. Various studies utilize regions away from the centerburst, 10,11 while others stress the inclusion of the centerburst. The appropriate window for an experiment, which is chosen to maximize the signal-to-noise ratio (SNR), depends on the analytes and instrumentation 10,11 and is usually chosen tens of points away from the centerburst.…”

“…Various studies utilize regions away from the centerburst, 10,11 while others stress the inclusion of the centerburst. The appropriate window for an experiment, which is chosen to maximize the signal-to-noise ratio (SNR), depends on the analytes and instrumentation 10,11 and is usually chosen tens of points away from the centerburst. 7,11 However, the region of the interferogram close to the centerburst, indicative of the transmitted intensity over the entire spectral bandwidth, is sensitive to both the total sample absorption and scattering effects.…”

Real‐time spectral evaluation for gaschromatography–Fourier transform infraredspectrometry

“…Days of scrutiny may be required before all useful information contained in this data is extracted and interpreted. The potential of GC/FT-IR for routine complex mixture analysis has motivated researchers to investigate possible methods for reducing operator intervention in the data evaluation process [7][8][9][10]. Recent emphasis has been placed on developing sensitive algorithms for generating gas chromatograms from interferometric information [11][12][13][14][15][16]].…”

FOURIER TRANSFORM INFRARED VIBRATIONAL SPECTROSCOPIC IMAGING: Integrating Microscopy and Molecular Recognition

“…Considerable discussion exists on the use of an appropriate region, or window, of the interferogram for calculating the G-S basis set and intensity (87). In particular, the size and position of this window may be critical to the predictive performance of the technique (87,88) and is usually chosen away from the centerburst (84,88). In imaging data sets, the region of the interferogram close to the centerburst is also indicative of the transmitted intensity over the entire spectral bandwidth.…”