Showing papers by "Peter R. Griffiths published in 2013"
TL;DR: It is demonstrated that by using a short-path background, data analysis is more resistant to interferences such as wavenumber shift or resolution alteration that occurs as a consequence of aging hardware or misalignment.
Abstract: The choice of the type of background spectrum affects the credibility of open-path Fourier transform infrared spectroscopy (OP/FT-IR) data, and consequently, the quality of data analysis. We systematically investigated several properties of the background spectrum. The results show that a short-path background measured with the lowest amplifier gain could significantly reduce noise in the calculated absorbance spectrum, by at least 30% in our case. We demonstrated that by using a short-path background, data analysis is more resistant to interferences such as wavenumber shift or resolution alteration that occurs as a consequence of aging hardware or misalignment. We discussed a systematic error introduced into quantitative analyses by the short-path background and developed a procedure to correct that error. With this correction approach, a short-path background established five years ago was still found to be valid. By incorporating these findings into the protocol for quantitative analysis, we processed the measurements with two OP/FT-IR instruments set up side by side in the vicinity of a large dairy farm, to monitor NH3, CH4, and N2O. The two sets of calculated concentrations showed high agreement with each other. The findings of our investigations are helpful to atmospheric monitoring practitioners of OP/FT-IR spectroscopy and could also be a reference for future amendments to the protocols outlined in the guidelines of the U.S. Environmental Protection Agency, the American Society for Testing and Materials, and the European Committee for Standardization.
10 citations
Journal Article•
TL;DR: In this article, a short-path background measured with the lowest amplifier gain was found to reduce noise in the calculated absorbance spectrum, by at least 30% in the case of OP/FT-IR data.
Abstract: The choice of the type of background spectrum affects the credibility of open-path Fourier transform infrared spectroscopy (OP/FT-IR) data, and consequently, the quality of data analysis. We systematically investigated several properties of the background spectrum. The results show that a short-path background measured with the lowest amplifier gain could significantly reduce noise in the calculated absorbance spectrum, by at least 30% in our case. We demonstrated that by using a short-path background, data analysis is more resistant to interferences such as wavenumber shift or resolution alteration that occurs as a consequence of aging hardware or misalignment. We discussed a systematic error introduced into quantitative analyses by the short-path background and developed a procedure to correct that error. With this correction approach, a short-path background established five years ago was still found to be valid. By incorporating these findings into the protocol for quantitative analysis, we processed the measurements with two OP/FT-IR instruments set up side by side in the vicinity of a large dairy farm, to monitor NH3, CH4, and N2O. The two sets of calculated concentrations showed high agreement with each other. The findings of our investigations are helpful to atmospheric monitoring practitioners of OP/FT-IR spectroscopy and could also be a reference for future amendments to the protocols outlined in the guidelines of the U.S. Environmental Protection Agency, the American Society for Testing and Materials, and the European Committee for Standardization.
8 citations
TL;DR: This work demonstrated that the accurate removal of baseline components is readily achievable with minimal user intervention and demonstrated flexibility in that prior information, such as the symmetry of a baseline-free VCD spectrum, is readily used during the correction protocol.
Abstract: A three-phase, computational method for the baseline correction of vibrational circular dichroism (VCD) spectra has been proposed. In the first phase the raw spectrum is subdivided into m segments (or regions) resulting in p rough estimates of the baseline. A second phase uses gradient characteristics to discriminate between baseline and band response for each baseline, in turn. In the final phase all baselines are interrogated simultaneously by assigning the median estimate of each differential response's distribution to the true baseline. Using VCD spectra of (R)-camphor as test cases, this work demonstrated that the accurate removal of baseline components is readily achievable with minimal user intervention. Baseline correction also demonstrated flexibility in that prior information, such as the symmetry of a baseline-free VCD spectrum, is readily used during the correction protocol. Although three adjustable parameters are present in the base algorithm, optimal performance and full automation were attainable following the use of analysis of variance (ANOVA) to analyze simulated bipolar spectra. These ANOVAs suggested that band point discrimination could be discarded and the remaining two default parameters adopted.
4 citations
01 Jan 2013
TL;DR: In this article, the authors describe three ways in which on-line infrared spectra of species eluting from a gas chromatograph (GC) are described in this chapter, including passing the effluent from the GC through a long, narrow gas cell, or lightpipe.
Abstract: Three ways in which on-line infrared (IR) spectra of species eluting from a gas chromatograph (GC) are described in this chapter. The first, and most simple, involves passing the effluent from the GC through a long, narrow gas cell, or light-pipe. Since vapor-phase spectra are measured using this technique, identification requires a library of vapor-phase reference spectra. The second technique, which is at least an order of magnitude more sensitive, involves adding a small amount of argon to the helium carrier and condensing the argon along with each chromatographically separated component on a moving gold-coated substrate and measuring the transflection spectrum. Bands in the matrix-isolated spectra of each component are very narrow but require a special library to allow spectral searching. The third, and most sensitive, technique involves condensing each component as a very small spot on a moving ZnSe window and measuring the transmission spectrum shortly after deposition. Spectra measured in this way are very similar to KBr disk reference spectra, for which extensive libraries are available. The detection limits may be reduced by at least an order of magnitude by vapor-depositing a thin layer of silver on the ZnSe plate.
2 citations