Concurrent Determination of Optical Constants and the Kramers-Kronig Integration Constant (Anchor Point) Using Variable-Angle ATR/FT-IR Spectroscopy

1992 ◽  
Vol 46 (12) ◽  
pp. 1848-1858 ◽  
Author(s):  
Lane D. Tickanen ◽  
M. Isabel Tejedor-Tejedor ◽  
Marc A. Anderson
Keyword(s):  
Refractive Index ◽  
Ir Spectroscopy ◽  
Optical Constants ◽  
Attenuated Total Reflection ◽  
Anchor Point ◽  
Separate Experiment ◽  
Absorption Bands ◽  
Variable Angle ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectroscopy has been used to determine optical constants in the infrared region of the spectrum for a variety of materials. Usually, the Kramers-Kronig transform is used to obtain optical constants from spectra, given that the baseline refractive index (anchor point) is known or can be determined. This determination often involves performing a separate experiment in which the refractive index of the sample is measured in a nonabsorbing region of the visible part of the spectrum, and the result extrapolated to the infrared. However, this is not feasible for opaque samples or for ones that contain domains large enough to scatter visible light. In this paper, we present a method for concurrently determining the anchor point and the optical constants using only variable-angle ATR/FT-IR spectroscopy and the subtractive form of the Kramers–Kronig transform. The method for determining the anchor point involves ratioing pATR (the negative log of the intensity of the ATR spectrum) values from weak absorption bands from spectra recorded at different angles of incidence. The anchor point can then be determined by computer. The only requirements are that the ATR system use unpolarized radiation and that the sample be thicker than the sampling depth of the IR radiation.

scholarly journals MOLECULAR COMPLEXES OF IVY TRITERPENE GLYCOSIDES WITH CHOLESTEROL

2018 ◽  
pp. 133-140 ◽  
Author(s):  
Леонид (Leonid) Александрович (Aleksandrovich) Яковишин (Yakovishin) ◽  
Владимир (Vladimir) Иванович (Ivanovich) Гришковец (Grishkovets)
Keyword(s):  
Ir Spectroscopy ◽  
Aqueous Ethanol ◽  
Molecular Complexes ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Triterpene Saponins ◽  
Absorption Bands ◽  
Ft Ir ◽  
Hederasaponin C ◽  
Ft Ir Spectroscopy

Molecular complexes of cholesterol with dominant triterpene saponins from members of the ivy genus Hedera L. (Araliaceae Juss.) – monodesmosidic glycoside α-hederin (hederagenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranoside) and bisdesmosidic glycoside hederasaponin C (hederagenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl-28-О-α-L-rhamnopyranosyl-(1→4)-О-β-D-glucopyranosyl-(1→6)-О-β-D-glucopyranoside) as well as with minor monodesmosidic glycoside hederoside F (hederagenin 3-О-β-D-glucopyranosyl-(1→2)-О-β-D-glucopyranoside) have been prepared. The complexation has been investigated by methods of isomolar series in the spectrophotometric version and FT-IR spectroscopy with a universal optical attenuated total reflection (ATR) accessory. It was shown that a-hederin, hederasaponin C and hederoside F form a 1 : 1 complexes with cholesterol, having a stability constants (5.6±0.1)×104, (4.7±0.1)×104 and (6.0±0.6)×104 M–1 respectively (in 70% aqueous ethanol et 25 °С). The constants are calculated on the basis of isomolar curves. The complexes of cholesterol with ivy monodesmosidic glycosides are more stable. Intermolecular interaction in the complexes is carried out by hydrogen bonds formation of type –С=О···Н–О– (for monodesmosidic glycosides) and –(Н)О···Н–О– (for bisdesmosidic glycoside). Hydrophobic contacts of the aglycone part of glycosides (hederagenin) with a lipophilic cholesterol molecule are possible. As a result, changes in some frequencies of the absorption bands of CH bonds are observed, which was established by IR spectroscopy.

scholarly journals Mesoporous Zirconia Coating for Sensing Applications Using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy

2021 ◽  
pp. 000370282110571
Author(s):  
Dominik Wacht ◽  
Mauro David ◽  
Borislav Hinkov ◽  
Hermann Detz ◽  
Andreas Schwaighofer ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Ir Spectroscopy ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
In Situ Monitoring ◽  
Zirconia Coating ◽  
Mesoporous Zirconia ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Mid-infrared attenuated total reflection (ATR) spectroscopy is a powerful tool for in situ monitoring of various processes. Mesoporous silica, an extensively studied material, has already been applied in sensing schemes due to its high surface area and tunable surface chemistry. However, its poor chemical stability in aqueous solutions at pH values higher than 8 and strong absorption below 1250 cm−1 limits its range of applications. To circumvent these problems, a mesoporous zirconia coating on ATR crystals was developed. Herein, the synthesis, surface modification, and characterization of ordered mesoporous zirconia films on Si wafers and Si-ATR crystals are presented. The modified coating was applied in sensing schemes using aromatic and aliphatic nitriles in aqueous solution as organic pollutants. The mesoporous zirconia coating shows strong chemical resistance when kept in alkaline solution for 72 h. The success of surface modification is confirmed using Fourier transform infrared (FT-IR) spectroscopy and contact angle measurements. Benzonitrile and valeronitrile in water are used as model analytes to evaluate the enrichment performance of the film. The experimental results are fitted using Freundlich isotherms, and enrichment factors of 162 and 26 are calculated for 10 mg L−1 benzonitrile and 25 mg L−1 valeronitrile in water, respectively. Limits of detection of 1 mg L−1 for benzonitrile and 11 mg L−1 for valeronitrile are obtained. The high chemical stability of this coating allows application in diverse fields such as catalysis with the possibility of in situ monitoring using FT-IR spectroscopy.

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