Optical Contact in ATR/FT-IR Spectroscopy

2001 ◽  
Vol 55 (10) ◽  
pp. 1352-1359 ◽  
Author(s):  
Sanong Ekgasit ◽  
Adchara Padermshoke
Keyword(s):  
Ir Spectroscopy ◽  
Air Gap ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Internal Reflection ◽  
Experimental Investigations ◽  
Transmission Spectra ◽  
Optical Contact ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Optical contact between an internal reflection element (IRE) and a sample is crucial for obtaining a good spectrum in an attenuated total reflection (ATR) experiment. When an air gap is present between the IRE and the sample, the spectrum severely deteriorates. Two techniques for determining the goodness of contact are proposed—first, by making a comparison between polarized ATR spectra and, second, by making a comparison between ATR and transmission spectra. When the optical contact is achieved, the normalized p-polarized ATR spectrum is exactly the same as the normalized s-polarized ATR spectrum. Moreover, the ratio between the normalized absorbance measured in the ATR mode and the normalized absorbance measured in the transmission mode equals the ratio between the frequency being considered and the normalization frequency. Theoretical and experimental investigations have been performed in order to verify the proposed techniques.

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.

Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy as an Analytical Method to Investigate the Secondary Structure of a Model Protein Embedded in Solid Lipid Matrices

2017 ◽  
Vol 72 (2) ◽  
pp. 268-279 ◽  
Author(s):  
Farrukh Zeeshan ◽  
Misbah Tabbassum ◽  
Lene Jorgensen ◽  
Natalie J. Medlicott
Keyword(s):  
Secondary Structure ◽  
Ir Spectroscopy ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Size Exclusion ◽  
Wet Granulation ◽  
Solid Lipid ◽  
Mixing Method ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Protein drugs may encounter conformational perturbations during the formulation processing of lipid-based solid dosage forms. In aqueous protein solutions, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy can investigate these conformational changes following the subtraction of spectral interference of solvent with protein amide I bands. However, in solid dosage forms, the possible spectral contribution of lipid carriers to protein amide I band may be an obstacle to determine conformational alterations. The objective of this study was to develop an ATR FT-IR spectroscopic method for the analysis of protein secondary structure embedded in solid lipid matrices. Bovine serum albumin (BSA) was chosen as a model protein, while Precirol AT05 (glycerol palmitostearate, melting point 58 ℃) was employed as the model lipid matrix. Bovine serum albumin was incorporated into lipid using physical mixing, melting and mixing, or wet granulation mixing methods. Attenuated total reflection FT-IR spectroscopy and size exclusion chromatography (SEC) were performed for the analysis of BSA secondary structure and its dissolution in aqueous media, respectively. The results showed significant interference of Precirol ATO5 with BSA amide I band which was subtracted up to 90% w/w lipid content to analyze BSA secondary structure. In addition, ATR FT-IR spectroscopy also detected thermally denatured BSA solid alone and in the presence of lipid matrix indicating its suitability for the detection of denatured protein solids in lipid matrices. Despite being in the solid state, conformational changes occurred to BSA upon incorporation into solid lipid matrices. However, the extent of these conformational alterations was found to be dependent on the mixing method employed as indicated by area overlap calculations. For instance, the melting and mixing method imparted negligible effect on BSA secondary structure, whereas the wet granulation mixing method promoted more changes. Size exclusion chromatography analysis depicted the complete dissolution of BSA in the aqueous media employed in the wet granulation method. In conclusion, an ATR FT-IR spectroscopic method was successfully developed to investigate BSA secondary structure in solid lipid matrices following the subtraction of lipid spectral interference. The ATR FT-IR spectroscopy could further be applied to investigate the secondary structure perturbations of therapeutic proteins during their formulation development.

Use of Attenuated Total Reflection—Fourier Transform Infrared Spectroscopy to Measure Collagen Degradation in Historical Parchments

2008 ◽  
Vol 62 (10) ◽  
pp. 1108-1114 ◽  
Author(s):  
Lee Gonzalez ◽  
Tim Wess
Keyword(s):  
Fourier Transform ◽  
Ir Spectroscopy ◽  
Conformational Changes ◽  
Structural Changes ◽  
Fourier Transform Infrared ◽  
Collagen Degradation ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

Developing a noninvasive method to assess the degraded state of historical parchments is essential to providing the best possible care for these documents. The conformational changes observed when collagen molecules, the primary constituent of parchment, unfold have been analyzed using attenuated total reflection–Fourier transform infrared (ATR-FT-IR) spectroscopy and the nanoscopic structural changes have been analyzed using X-ray diffraction (XRD). The relationship between the results obtained from these techniques was studied using principal component analysis, where correlation was found. The extent of gelatinization of historical parchments has been assessed using ATR-FT-IR and XRD and the frequency shifts observed as collagen degrades into gelatin have been reported. These results indicate that collagen degradation can be measured noninvasively in parchment and demonstrate the utility of ATR-FT-IR spectroscopy as a method to investigate historical documents.

Sign in / Sign up

Export Citation Format

Share Document