Showing papers in "Applied Spectroscopy in 1985"
TL;DR: In this article, a multi-wavelength concept for optical correction (Multiplicative Scatter Correction, MSC) is proposed for separating the chemical light absorption from the physical light scatter.
Abstract: This paper is concerned with the quantitative analysis of multicomponent mixtures by diffuse reflectance spectroscopy. Near-infrared reflectance (NIRR) measurements are related to chemical composition but in a nonlinear way, and light scatter distorts the data. Various response linearizations of reflectance (R) are compared (R with Saunderson correction for internal reflectance, log 1/R, and Kubelka-Munk transformations and its inverse). A multi-wavelength concept for optical correction (Multiplicative Scatter Correction, MSC) is proposed for separating the chemical light absorption from the physical light scatter. Partial Least Squares (PLS) regression is used as the multivariate linear calibration method for predicting fat in meat from linearized and scatter-corrected NIRR data over a broad concentration range. All the response linearization methods improved fat prediction when used with the MSC; corrected log 1/R and inverse Kubelka-Munk transformations yielded the best results. The MSC provided simpler calibration models with good correspondence to the expected physical model of meat. The scatter coefficients obtained from the MSC correlated with fat content, indicating that fat affects the NIRR of meat with an additive absorption component and a multiplicative scatter component.
1,309 citations
TL;DR: In this paper, the statistical technique of principal components is used to analyze two sets of near-infrared spectra, wheat flour samples for which % moisture and % protein values are included, and milled barley samples for whose hot water extract values were included.
Abstract: The statistical technique of principal components is used to analyze two sets of near-infrared spectra, wheat flour samples for which % moisture and % protein values are included, and milled barley samples for which hot water extract values are included. The methodology and interpretation of this technique are described within the context of NIR data, and its advantages both in providing insight into the variation of the spectra, and as a method of avoiding the problems caused by highly correlated reflectance energy values in the derivation of calibration equations, are highlighted. In each set of samples the first principal component accounts for the vast majority of the variation. These components also have an almost identical shape, which is interpreted as reflecting particle size. The second wheat component and the third barley component are also almost identical, with a shape very similar to that of the spectrum of water. Both fourth components share peaks at points in the spectrum which are used by fixed-filter instruments to measure protein in cereals.
266 citations
TL;DR: In this article, a linear least-squares approximation to nonlinearities in the Beer-Lambert law is made by allowing the reference spectra to be a set of known mixtures.
Abstract: In an extension of earlier work, weighted multivariate least-squares methods of quantitative FT-IR analysis have been developed. A linear least-squares approximation to nonlinearities in the Beer-Lambert law is made by allowing the reference spectra to be a set of known mixtures. The incorporation of nonzero intercepts in the relation between absorbance and concentration further improves the approximation of nonlinearities while simultaneously accounting for nonzero spectral baselines. Pathlength variations are also accommodated in the analysis, and under certain conditions, unknown sample pathlengths can be determined. All spectral data are used to improve the precision and accuracy of the estimated concentrations. During the calibration phase of the analysis, pure component spectra are estimated from the standard mixture spectra. These can be compared with the measured pure component spectra to determine which vibrations experience nonlinear behavior. In the predictive phase of the analysis, the calculated spectra are used in our previous least-squares analysis to estimate sample component concentrations. These methods were applied to the analysis of the IR spectra of binary mixtures of esters. Even with severely overlapping spectral bands and nonlinearities in the Beer-Lambert law, the average relative error in the estimated concentrations was <1%.
223 citations
TL;DR: In this article, the composition and surface structure of soot derived from the combustion of n-hexane have been examined by FT-IR, Raman, 13C CP/MAS NMR, and EPR spectroscopies.
Abstract: Soot produced from the combustion of fossil fuels, widely distributed in the atmosphere, is significantly different from most carbons for which the surface structure and/or reactivity have been studied The composition and surface structure of soot derived from the combustion of n-hexane have been examined by FT-IR, Raman, 13C CP/MAS NMR, and EPR spectroscopies as well as through desorption measurements Carbon-oxygen functionalities on the fresh carbon surface include acid anhydride, a carbonyl conjugated with an aromatic segment, an alkylketone, and aryl ether linkages Also present, confirmed by isotopic substitution, is a quantity of unsaturated C-H, dependent upon the combustion conditions The degree of aromaticity and the graphitic nature of this soot have been determined
214 citations
TL;DR: Fourier selfdeconvolution (FSD) has been employed to enhance the resolution of the infrared spectra of proteins in the solid state and in D2O solution as mentioned in this paper.
Abstract: Fourier self-deconvolution (FSD) has been employed to enhance the resolution of the infrared spectra of proteins in the solid state and in D2O solution. The feasibility of using diffuse reflectance spectrometry for measuring the infrared spectra of solid proteins has been demonstrated. FSD permits inherently broad absorption bands to be resolved into distinct peaks which can be associated with specific protein secondary structures. Because the areas of the resolved peaks are the same as the areas of the previously unidentifiable components, this new method should enable quantitative estimates of the proportion of each conformation in a protein to be calculated.
168 citations
TL;DR: In this article, the CIRCLE ATR accessory has been used to measure the optical and dielectric constants of organic liquids and water, and the agreement between the results obtained and literature values is shown to be adequate for chemical use.
Abstract: The CIRCLE ATR accessory has been used to measure the optical and dielectric constants of organic liquids and water. The method, based on Fresnel's equations, is described in detail, and the agreement between the results obtained and literature values is shown to be adequate for chemical use. The utility of optical and dielectric constants for the calculation of traditional infrared intensities in liquids and of dipole moment derivatives is outlined.
146 citations
TL;DR: In this paper, a method is presented which allows the FT-IR spectrum of a material to be related to many of the significant practical properties of that material by using factor analysis of all or part of the spectra of a calibration set of well-characterized samples.
Abstract: A method is presented which allows the FT-IR spectrum of a material to be related to many of the significant practical properties of that material. The method uses factor analysis of all or part of the spectra of a calibration set of well-characterized samples to determine the minimum set of factors and the associated factor loadings required to reproduce the spectra. Multiple linear regression of the factor loadings against measured properties gives close correlations which are used to predict the properties of unknown samples similar to those constituting the base set. The method is often fast compared with conventional techniques and, by suitable choice of calibration sets, can give semiquantitative results for a widely varying set of samples, or quantitative results of accuracy comparable with conventional techniques for a calibration set and unknowns from a narrower range of samples. Examples of the use of the method are given for coal, bauxite, manganese dioxide ore, and diesel fuel.
130 citations
TL;DR: In this paper, the Fourier transform infrared spectra of aqueous systems were studied using a diamond anvil cell, and the pressure effects on the vibrational dynamics in these systems were investigated.
Abstract: Raman spectra of aqueous phospholipid bilayers and aqueous micellar solution of surfactants at high pressure have been studied in this laboratory. However, some normal modes in these systems are Raman inactive or weakly active, and most of the normal modes of the methylene chains in these systems are highly dispersed. In order to further understand the pressure effects on the vibrational dynamics in these systems, we have extended our pressure studies to the Fourier transform infrared spectra of these aqueous systems, using a diamond anvil cell.
129 citations
IBM1
TL;DR: A thin-layer electrochemical cell which allows for the convenient measurement of infrared reflection-absorption spectra (IRRAS) of the electrode/electrolyte interphase has been designed and built as discussed by the authors.
Abstract: A thin-layer electrochemical cell which allows for the convenient measurement of infrared reflection-absorption spectra (IRRAS) of the electrode/electrolyte interphase has been designed and built. In order to minimize the thickness of the electrolyte in front of the electrode surface, one mounts the working electrode on the end of a piston so that it can be pressed against an infrared window. Infrared radiation is then reflected from the electrode surface via the infrared window without experiencing severe attenuation due to the electrolyte. Contaminants are minimized by the machining of both the cell body and piston from an inert fluorocarbon plastic. Calcium fluoride was chosen as the window material because of its transparency, its low refractive index, and its low solubility in aqueous electrolyte. The use of this cell in a Fourier transform infrared reflection-absorption spectrometer utilizing polarization modulation is described. The IRRAS spectra obtained from this cell have been analyzed with the use of the generalized Fresnel equations for stratified media. Some of the computational results for the water/silver electrode interphase are used to interpret the measured spectra of water near the electrode. The discussion includes infrared intensity distributions in aqueous media and their influence on the IRRAS measurement.
126 citations
TL;DR: In this paper, the polarization effect of one or several tilted, parallel air-spaced fused silica plates is calculated for the calibration of differential linear dichroism (LD) in the measurement ranges 10−3 to 10−1 decadic absorbance units and the wavelength region 200-700 nm.
Abstract: The polarization effect of one or several tilted, parallel air-spaced fused silica plates is calculated. It is generally necessary to include higher order reflections. A device consisting of 1-4 plates tilted 10-45° from normal incidence is proposed for the calibration of differential linear dichroism (LD) in the measurement ranges 10−3 to 10−1 decadic absorbance units and the wavelength region 200-700 nm. The experimental LD measured in these ranges on commercial circular dichrometers, converted to LD mode according to Norden and Davidsson, was in excellent agreement with the calculated, nonempirical results. Since the response function of the instrument in this conversion mode is the same for LD and CD, the method also provides a means for absolute calibration of CD. The results can also be applied to polarized scattering and fluorescence. (For previous papers on this theme, see Refs. 6, 9 and 12.)
99 citations
TL;DR: In this paper, a method is described whereby the wealth of information present in the Fourier transform infrared spectrum of a material may be extracted and used to estimate useful properties of the material.
Abstract: A method is described whereby the wealth of information present in the Fourier transform infrared spectrum of a material may be extracted and used to estimate useful properties of the material. Factor analysis is used to condense the data, after which the use of multiple linear regression allows correlations to be established for a calibration set, from which properties of unknown samples can be estimated.
TL;DR: In this article, a method was described for the instantaneous concentration measurement of formaldehyde (H2CO) in air by laser-induced fluorescence of the H2CO (A1A″-X˜1A1) electronic transition.
Abstract: A method is described for the instantaneous concentration measurement of formaldehyde (H2CO) in air by laser-induced fluorescence of the H2CO (A1A″-X˜1A1) electronic transition. Concentrations down to about 13 ng/litre (about 10 ppb) can be determined in about 100 seconds without any sample collection, water extraction, or further chemical treatment. The influence of the presence of water vapor and methanol vapor in the air on the accuracy of the method has been investigated. It appeared that if the humidity of the ambient air is not taken into account, the detection limit is about 0.15 ppm H2CO in air; the presence of methanol has no influence on the accuracy.
TL;DR: In this paper, Fourier transform infrared spectroscopy was used to analyze thin films of poly(vinyl chloride), poly(methyl methacrylate), and poly(styrene) and the interference fringes present in the transmission spectra of these samples were used to determine film thickness and average refractive index.
Abstract: Thin films of poly(vinyl chloride), poly(methyl methacrylate), and poly(styrene) were analyzed by Fourier transform infrared spectroscopy. The interference fringes present in the transmission spectra of these samples were used to determine film thickness and average refractive index. Subsequent Kramers-Kronig analysis of these transmission spectra provided the dispersion of the refractive index and the absorption index across the entire mid-infrared region. Interference fringes were absent in the optical constant spectra, and good agreement was obtained between our optical constant spectra and those of other authors.
TL;DR: In this article, a simple method is described for the approximate measurement of the ion energy distribution in an inductively coupled plasma-mass spectrometer (ICP-MS) with a continuum flow sampling interface.
Abstract: A simple method is described for the approximate measurement of the ion energy distribution in an inductively coupled plasma-mass spectrometer (ICP-MS) with a continuum flow sampling interface. The average ion kinetic energy, kinetic energy spread, and maximum kinetic energy are evaluated from a plot of ion signal as a function of retarding voltage applied to the quadrupole mass analyzer. The effects of plasma operating parameters on ion signals and energies are described. In particular, kinetic energy is a sensitive function of aerosol gas flow rate. This behavior is attributed to a nonthermal, possibly electrical, interaction between the plasma and the sampling interface, which is induced by the presence of the axial channel in the ICP.
TL;DR: In this paper, an experimental investigation has been made of the relation of absorbance of a band in FT-IR/ATR spectroscopy to the thickness of the probed surface layer from the measurements of two-layered samples.
Abstract: Experimental investigation has been made of the relation of absorbance of a band in FT-IR/ATR spectroscopy to the thickness of the probed surface layer from the measurements of two-layered samples The two layered samples are composed of a polystyrene surface layer varying in thickness from 001 to 364 μm and a polyurethane base layer of 100 μm thickness The component spectrum of the surface or base layer was separated by spectral subtraction FT-IR/ATR spectroscopic measurements were mostly measured by nonpolarized incident light The relation of observed absorbances of several selected bands of both the surface and base layers to the thickness of the surface layer was compared with the theoretical calculations from Harrick's equation In the comparison, the effect of "nonpolarization" of the incident light was corrected for the observed absorbances The agreement was excellent between the observation of and the theoretical calculation for both the surface and base layers A method was proposed to determine the thickness of the spectrally separable surface layer on a film The usefulness of this method was demonstrated by application to the redetermination of the thickness of the surface layer of the present two-layered samples An expression was proposed to give the contribution of a surface layer of a certain thickness to the total absorbance of a band in ATR spectroscopy
TL;DR: In this article, a method was developed to spectrochemically analyze beryllium particles on filters using the laser spark, which formed on the filter by a cylindrical lens, is 0.1-mm wide and 4- to 8mm long.
Abstract: A method has been developed to spectrochemically analyze beryllium particles on filters using the laser spark. The spark, formed on the filter by a cylindrical lens, is 0.1-mm wide and 4- to 8-mm long. By the rotation of the filter under the spark, a large area can be sampled in only a few minutes. The surface detection limit (SNR = 6) for particles 0.5-5 μm in diameter is 0.45 ng/cm2, which corresponds to 3.6 ng total Be mass on the exposed area (32-mm diam.) of a 37-mm-diam. filter. The RSD for replicate sample analysis is 4%. Several methods of calibrating the technique are discussed. The effects of particle size and some contaminants on the analysis are described. The usefulness of this method for monitoring airborne beryllium concentrations is considered.
TL;DR: The determination of salinity via NIRA is attractive for two reasons as discussed by the authors, namely, its simplicity and its compatibility with remote measurements from airplanes or the earth's orbit suggests a number of ecological, oceanographic, or naval applications.
Abstract: The determination of salinity via NIRA is attractive for two reasons. On one hand, NIRA's stark simplicity (little or no sample preparation, 20 s analysis time) makes it a desirable technique for salinity determination in foodstuffs, forage, or biological samples. On the other hand, the technique's compatibility with remote measurements from airplanes or the earth's orbit suggests a number of ecological, oceanographic, or naval applications.
TL;DR: In this article, a model of hexane soot as formed in flame is proposed on the basis of this work, which is based on the model proposed in this paper and discussed in detail in Section 2.1.
Abstract: Successive extraction of soluble components of hexane soot with a suite of solvents has been followed by CGC/MS, FT-IR, UV/Vis, fluorescence, and NMR spectroscopic analysis of these extracts. From these studies, additional understanding of the structure and reactivity of this material has emerged. A significant portion of the soot is extractable as polynuclear aromatic and aliphatic compounds, while the nonextractable solid structure, with both aromatic and aliphatic portions, contains such carbon-oxygen functionalities as acid anhydride, carbonyl, and ether linkages. A model of hexane soot as formed in flame is proposed on the basis of this work.
TL;DR: In this paper, atomic spectrometers are classified into three classes: atomic absorption, atomic emission, and atomic fluorescence, with the latter two more amenable to multielement analyses.
Abstract: The importance of trace elements in environmental, nutritional, clinical, forensic, toxicological, and other fields has been well recognized. Among the variety of analytical techniques available for trace element determinations, atomic spectrometry is one of the most popular. This technique may further be divided into atomic absorption, atomic emission, and atomic fluorescence, with the latter two more amenable to multielement analyses. These atomic techniques require the introduction of samples into a high-temperature atom reservoir where atomic (or ionic) vapors are produced. These high-temperature atom sources include flames; the inductively coupled plasma, ICP; microwave-induced plasma, MIP; direct current plasma, DCP; and the graphite furnace.
TL;DR: In this article, the design and performance characteristics of a continuous-flow vapor generation accessory for atomic absorption spectrophotometry are reported, which provides analytical sensitivity for mercury, arsenic, selenium, antimony, bismuth, tellurium and tin equal or superior to that of a batch-type vapor generation device.
Abstract: The design and performance characteristics of a continuous-flow vapor generation accessory for atomic absorption spectrophotometry are reported. When used with a conventional atomic absorption spectrophotometer, the accessory provides analytical sensitivity for mercury, arsenic, selenium, antimony, bismuth, tellurium, and tin equal or superior to that of a batch-type vapor generation device. Sample presentation, sample consumption, precision of measurement, and simplicity of operation are similar to those of flame atomic absorption with a pneumatic nebulizer. Details of the construction of the continuous-flow manifold, gas/liquid separator, and absorption cells are discussed, and the effects of reagent concentrations and carrier gas flow rates are shown. Characteristic concentrations and analytical curves for the above elements are also presented.
TL;DR: In this paper, the depolarization ratios of the Raman bands of isotropic samples are in good agreement with those obtained with the use of conventional instruments, provided that the reflection or transmission factor of the beamsplitter is introduced as a correction.
Abstract: Polarized Raman spectra of the reference materials carbon tetrachloride and α-quartz are obtained with the Raman microprobe MOLE with the use of different high-numerical-aperture objectives. The depolarization ratios of the Raman bands of isotropic samples are in good agreement with those obtained with the use of conventional instruments, provided that the reflection or transmission factor of the beamsplitter is introduced as a correction. Even with the very wide-aperture objectives used, the depolarization effect is not large and can be evaluated theoretically. Correct polarized spectra of anisotropic samples can also be obtained with a Raman microspectrometer. Here again, the depolarization effect induced by the wide-aperture objective is not large and can be evaluated theoretically if the birefringence of the crystal does not play a significant role. The depolarization induced by the birefringence is especially important when incident and scattered light propagate in a direction close to the optical axis of the crystal, but can be minimized by a reduction of the optical path within the sample.
TL;DR: The HPLC-HY-DCP as discussed by the authors approach is applicable for organotin compounds such as mono-, di-, and trimethyltin chloride, as well as stannous and stannic cations.
Abstract: Total tin determinations can be accomplished at trace levels (10-25 ppb) by a continuous on-line hydride generation (HY), followed by direct current plasma (DCP) emission spectroscopy (HY-DCP). This approach is applicable for organotin compounds such as mono-, di-, and trimethyltin chloride, as well as stannous and stannic cations. HY-DCP methods of total tin analysis have been applied to a number of spiked and actual samples. Detection limits, calibration plots, sensitivities, and related analytical parameters have been evaluated. Organotin analysis and speciation can be accomplished by the interfacing of this HY-DCP step with high-performance liquid chromatography (HPLC), with the use of a polymeric PRP-1 type column with an acidic, ionic mobile phase, usually containing a suitable ion-pairing reagent. The overall speciation approach, HPLC-HY-DCP, has been evaluated with regard to separation conditions; detection limits; sensitivities; calibration plots; and applications to spiked water, clam juice, seawater, and tuna fish samples. The results suggest the suitability and reliability of this HPLC-HY-DCP approach for individual tin species. Other metal species capable of forming a hydride derivative on-line, in a continuous fashion, may also be suitable for speciation by HPLC-HY-DCP.
TL;DR: In this article, the source of optical artifacts in circularly polarized luminescence was examined by application of the method of Mueller matrices, and it was shown that the artifacts in most cases are due to the small inherent birefringence in the photoelastic modulator employed in the experimental measurement.
Abstract: The source of optical artifacts in circularly polarized luminescence is examined by application of the method of Mueller matrices. Expressions for the circularly polarized luminescence intensity are developed that illustrate that the source of the artifact in most cases is due to the small inherent birefringence in the photoelastic modulator employed in the experimental measurement. Experimental results are presented that are consistent with this conclusion.
IBM1
TL;DR: Theoretical extensions to the reflectivity ratio, (R − R0)/R0, for a number of metals have been made and indicate the optimal conditions for each experiment as mentioned in this paper.
Abstract: Infrared spectra of thin films (<200 A) on metals have been observed with Fourier Transform IR spectroscopy (FT-IR) by improvements to the grazing incidence reflection methods proposed by Greenler. Theoretical extensions to the reflectivity ratio, (R − R0)/R0, for a number of metals have been made and indicate the optimal conditions for each experiment. Grazing incidence reflection measurements of poly(methyl methacrylate) (PMMA) films (thickness 180 A) have been made on silver-, aluminum-, copper-, and chromium-coated substrates. Although the reflectivity ratio maximizes at an angle which deviates a few degrees from pure grazing, filling factor considerations and optimal optical fields show both experimentally and theoretically that operating some ten degrees away from grazing gives better signal-to-noise spectra for reasonable accumulation times. Furthermore, a shift in the maximum of the reflectivity ratio curve is observed from one metal to another, and a comparison between silver and chromium is used to illustrate this effect on the observed IR spectra.
TL;DR: In this paper, a microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas, and a concentric tube torch was constructed so the plasma could be easily ignited and maintained.
Abstract: A microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas A concentric tube torch was constructed so the plasma could be easily ignited and maintained This new plasma emission source has a flame-like appearance and extends 10 cm beyond the cavity, at an applied power of 250 W The nitrogen plasma readily accepts aerosol samples and is compatible with sample introduced from a conventional nebulizer system The radial (side-on) optical viewing configuration was found to have lower background emission than the more commonly employed axial (end-on) configuration Optimum operating conditions were established from the effects of applied power, flow rate, and signal-to-background noise on the intensity of both atom and ion transitions A discussion of the background spectral features and the analytical potential of this new source is presented
TL;DR: In this paper, a laser-induced fluorescence (LIF) detector is evaluated for use with high-efficiency liquid chromatography columns of capillary dimensions, which is capable of sensing femtogram amounts of coumarin 440, and the response is linearly related to concentration over at least eight orders of magnitude.
Abstract: A laser-induced fluorescence (LIF) detector is evaluated for use with high-efficiency liquid chromatography columns of capillary dimensions. This detector employs a cw helium-cadmium laser (325 nm, 5-10 mW) as the excitation source, together with a fused-silica capillary flowcell and filter/photomultiplier optical system. The flowcell, which is an integral part of the microcolumn, contributes from 0.06 nL2 to 0.06 μL2 variance to the chromatographic system for capillaries of 35 to 330 μm diameter, respectively. The LIF detector is capable of sensing femtogram amounts of coumarin 440, and the response is linearly related to concentration over at least eight orders of magnitude. The potential of this combination of analytical techniques is demonstrated through the analysis of multicomponent mixtures of derivatized fatty acids and prostaglandins at the pico- and subpicomole level.
TL;DR: In this article, the authors show that the Kubelka-munk relationship does not account for specular reflectance, which is simply the energy reflected from the front surface of the sample.
Abstract: The Kubelka-Munk relationship is the equation most commonly used to describe the reflectance from a scattering medium. This equation breaks down, however, in several important situations in the mid-infrared. Most notably, the relationship does not account for specular reflectance, which is simply the energy reflected from the front surface of the sample. When a sample reflects diffusely and specularly, as do all real-world samples, there is a specular reflectance spectrum superimposed on the diffuse reflectance spectrum, and deviations from this equation occur. In the case of organic samples, this causes a curved line (concave downward) for the plot of f(R∞) or Kubelka-Munk units vs. sample weight percent in a nonabsorbing matrix. For inorganic samples, the effect can be more severe. Since the specular reflectance of inorganic bands can be much greater than organics, often complete band inversions (reststrahlen bands) or derivative shaped peaks result. In either case, quantitative analysis is not straightforward, and in the latter case, even qualitative interpretation is difficult.
TL;DR: In this paper, diffuse reflectance infrared spectroscopy can be used to characterize materials without recourse to extensive sample preparation, and the applicability of this sampling approach is demonstrated on a variety of diffusely scattering solids including bulk powders and foams.
Abstract: The technique of diffuse reflectance infrared spectroscopy can be used to characterize materials without recourse to extensive sample preparation. The applicability of this sampling approach is demonstrated on a variety of diffusely scattering solids including bulk powders and foams. The technique is also applied to the identification of chromatographically (HPLC and TLC) separated fractions.
TL;DR: In this paper, a method for determining the component spectra from a set of unknown two-component mixture spectra is proposed, which is considered as an advanced version of the Lawton-Sylvestre self-modeling curve resolution.
Abstract: A method is proposed for determining the component spectra from a set of unknown two-component mixture spectra. This method is considered as an advanced version of the Lawton-Sylvestre self-modeling curve resolution. The disadvantage of the weakness against noise is overcome by the introduction of the concept of filtering; the uncertainty of the solution is removed by the reduction of the band for each curve to a single curve with aid of the concept of entropy minimization. Experimental results with infrared absorption spectra of xylene isomer mixtures and visible absorption spectra of dye mixtures demonstrate the power of this method.
TL;DR: In this paper, the authors explored the quantitative aspects of diffuse reflectance FT-IR for standard E-glass/AAPS (N-2-aminoethyl-3-aminopropyltrimethoxysilane) treated samples.
Abstract: The quantitative aspects of diffuse reflectance FT-IR are explored for standard E-glass/AAPS (N-2-aminoethyl-3-aminopropyltrimethoxysilane) treated samples. Nondestructive sample preparation procedures are used. One generates calibration curves by plotting the normalized integrated intensity of the coupling agent bands in the 2990-2800 and 1700-1500 cm−1 regions vs. the concentration of the treatment solution. The data are derived by DRIFT spectroscopy, and the above results are plotted for the overlayer technique as well as for no overlayer. The scatter in the quantitative data due to fiber orientation effects has been measured and is found to be significant (20-30%). However, averaging over several orientations of the fibers results in a linear dependence of the integrated intensities of the coupling agent bands on solution concentration. The well-known breakpoint that has been observed for other coupling agent systems does not appear in the curve derived from the averaged spectra. The above-mentioned scatter is eliminated by the use of KBr overlayers on the samples. Linear calibration curves relating band intensity to concentration can be constructed. When the overlayer procedure is used, breakpoints do occur in the calibration curves. The position of these breakpoints agrees well with observations for the similar coupling agent γ-APS.