Optical UV Derivative Spectroscopy for Monitoring Gaseous Emissions

Vogt, Frank; Klocke, U.; Rebstock, K; Schmidtke, G.; Wander, V.; Tacke, M.

doi:10.1366/0003702991945966

Cited by 24 publications

(29 citation statements)

References 16 publications

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“…[15][16][17][18][19] While these methods proved to be less sensitive than conventional chromatographic analysis, there is an undoubted potential for discontinuous on-site pollution measurements due to the availability of field-deployable instrumentation. Direct detection of aromatic hydrocarbons in water based on UV 20,21 However, field applicability of this transmission-based method may be restricted due to a potential influence of turbidity in real-world samples.…”

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confidence: 99%

Simultaneous Quantitative Determination of Benzene, Toluene, and Xylenes in Water Using Mid-Infrared Evanescent Field Spectroscopy

2004

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Attenuated total reflection mid-infrared spectroscopy is applied for simultaneous detection and quantification of the environmentally relevant analytes benzene, toluene, and the three xylene isomers. The analytes are enriched into a thin polymer membrane coated onto the surface of an internal reflection waveguide, which is exposed to the aqueous sample. Direct detection of analytes permeating into the polymer coating is performed by utilizing evanescent field spectroscopy in the fingerprint range (>10 microm) of the mid-infrared (MIR) spectrum (3-20 microm) without additional sample preparation. All investigated compounds are characterized by well-separated absorption features in the evaluated wavelength regime. Hence, data evaluation was performed by integration of the respective absorption peaks. Limits of detection lower than 20 ppb (v/v) for all xylene isomers, 45 ppb (v/v) for benzene, and 80 ppb (v/v) for toluene have been achieved. The straightforward experimental setup and the achieved detection limits for these environmentally relevant volatile organic compounds in the low-ppb concentration range reveal a substantial potential of MIR evanescent field sensing devices for on-line in situ environmental analysis.

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confidence: 99%

Simultaneous Quantitative Determination of Benzene, Toluene, and Xylenes in Water Using Mid-Infrared Evanescent Field Spectroscopy

2004

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“…In this case acetone was considered as uncalibrated absorber. The second example dealt with ultraviolet (202±217 nm) second derivative spectroscopy [6] analyzing gaseous mixtures of SO 2 , NH 3 and NO. Here NO was used as uncalibrated absorber.…”

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Secured PCR (sPCR) for detection and correction of PCR calibration model failures induced by uncalibrated spectral features

Vogt

Mizaikoff

2003

Journal of Chemometrics

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Many spectroscopic monitoring techniques make use of chemometric algorithms such as principal component regression (PCR) for calibration and evaluation of optical spectra. However, standard techniques of chemometric calibration and evaluation suffer from uncalibrated spectral features which are contained in measured spectra but were not considered during the initial calibration. For two main reasons such uncalibrated spectral features have to be detected and corrected: (a) if unknown spectral features appear after calibration major errors of concentration prediction are encountered and (b) the detection of uncalibrated spectral features enables recognition and handling of failures occurring in chemical processes. Hence detection, correction and characterization of uncalibrated absorption features are of great importance in on-line spectroscopy. A novel approach is proposed here for this purpose. This algorithm performs a qualitative data analysis for detecting and correcting such uncalibrated spectral features. Following this qualitative data analysis and if necessary correction, a conventional PCR is used for calculating the concentration of the calibrated analytes. Both steps together set up a so-called secured PCR (sPCR). In the undisturbed case this sPCR algorithm is demonstrated to provide equivalent results as conventional PCR and to be superior in evaluating disturbed spectra. For testing purposes simulated spectra sets are used since the disturbance is known and the determined results can be validated with respect to the magnitude of the true disturbance. The errors averaged over 1000 disturbed test samples could be decreased up to 71% by sPCR compared with conventional PCR. In up to 94% of the test samples more accurate concentration values were obtained. The novel sPCR algorithm was also applied to experimental spectra measured with mid-infrared attenuated total reflection spectroscopy considering chlorinated hydrocarbons dissolved in water. sPCR is capable to extract uncalibrated features from these experimental data and to improve the concentration results.

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“…This is feasible because an explicit data model is rarely required for quantitative predictions or for sample classification. In soft-modeling procedures, nonlinear relations between measured data and the wanted chemical information can be empirically approximated for instance by a piecewise linear model [9] or by multivariate, polynomial models [10][11][12]. While successful for many quantitative calibrations, due to the absence of an interpretable model function, soft modeling cannot gain insights into the underlying chemical processes.…”

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confidence: 99%

A self‐guided search for good local minima of the sum‐of‐squared‐error in nonlinear least squares regression

Vogt

2014

Journal of Chemometrics

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Hard modeling of nonlinear chemical or biological systems is highly relevant as a model function together with values for model parameters provides insights in the systems' functionalities. Deriving values for said model parameters via nonlinear regression, however, is challenging as usually one of the numerous local minima of the sum-of-squared errors (SSEs) is determined; furthermore, for different starting points, different minima may be found. Thus, nonlinear regression is prone to low accuracy and low reproducibility. Therefore, there is a need for a generally applicable, automated initialization of nonlinear least squares algorithms, which reaches a good, reproducible solution after spending a reasonable computation time probing the SSE-hypersurface.For this purpose, a three-step methodology is presented in this study. First, the SSE-hypersurface is randomly probed in order to estimate probability density functions of initial model parameter that generally lead to an accurate fit solution. Second, these probability density functions then guide a high-resolution sampling of the SSE-hypersurface. This second probing focuses on those model parameter ranges that are likely to produce a low SSE. As the probing continues, the most appropriate initial guess is retained and eventually utilized in a subsequent nonlinear regression.It is shown that this "guided random search" derives considerably better regression solutions than linearization of model functions, which has so far been considered the best-case scenario. Examples from infrared spectroscopy, cell culture monitoring, reaction kinetics, and image analyses demonstrate the broad and successful applicability of this novel method.

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Optical UV Derivative Spectroscopy for Monitoring Gaseous Emissions

Cited by 24 publications

References 16 publications

Simultaneous Quantitative Determination of Benzene, Toluene, and Xylenes in Water Using Mid-Infrared Evanescent Field Spectroscopy

Simultaneous Quantitative Determination of Benzene, Toluene, and Xylenes in Water Using Mid-Infrared Evanescent Field Spectroscopy

Secured PCR (sPCR) for detection and correction of PCR calibration model failures induced by uncalibrated spectral features

A self‐guided search for good local minima of the sum‐of‐squared‐error in nonlinear least squares regression

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