Infrared (IR) Spectroscopy

The beginning of the age of Fourier transform infrared (FT-IR) spectroscopy meant the availability of digital spectra and opened the possibility of using computers to compare a single spectrum against a reference database containing thousands of spectra, thereby allowing enormous efficiency gains in the comparison of unknown spectra to reference materials. Various algorithms can be used to create a hit quality index (HQI), which is a measure of how well the query spectrum compares against each reference spectrum.

Infrared reflection spectroscopy is a tool that can be used to study coated plastics, but the spectra can show unexpected features. In this report, we calculate the specular reflectance for a flat surface of two different polymers as well as how their spectra change when the other polymer is added as a film with a thickness of up to 2.5 ?m. One of the unusual phenomena we observe is that "derivative"-shaped substrate bands invert in sign as the other polymer is added as a coating. We also show how the reflection of the surface changes and becomes polarized as the angle of incidence increases.

Self-assembled monolayers (SAMs) can be applied in a variety of technical areas. Infrared characterization of these materials is a challenge because of the low concentrations on the surfaces. This article reviews the sampling methods for characterization and presents data comparing the different approaches.

The micro attenuated total reflectance (ATR) chemical imaging of polymers, in particular polymer laminates, typically requires significant pressure to ensure good sample-to-ATR crystal contact. For thin cross-sectioned materials, ensuring structural rigidity against this pressure requires significant sample preparation, such as resin embedding, cutting, and polishing.

Bernhard Lendl and Cosima Koch of the Vienna University of Technology have developed a new method for on-line monitoring of fermentations using mid-infrared spectroscopy.

Part of a new podcast series presented in collaboration with the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS), in connection with SciX 2012 ? the Great Scientific Exchange, the North American conference (39th Annual) of FACSS.

A review of the application of IR spectroscopy for the analysis of color components in winemaking, and the contribution of spectral preprocessing to improve the multivariate calibration.

By combining atomic force microscopy (AFM) and infrared (IR) spectroscopy, one can attain spatial resolution improvements of two orders of magnitude over traditional IR spectroscopy.

The series on classical least squares continues with a comparison of experimental results and theoretical expectations.

Case studies involving fouling and product quality illustrate the effective use of this method.

Continued discussion of the classical least squares approach to calibration, with a focus on the reconstruction of mixtures

How can you navigate the maze of choices for detecting molecular vibrations with mid-infrared (IR), near IR (NIR), and visible (Raman)? Understanding what is being measured, how it is measured, and the advantages and disadvantages of each technique, will help.

When combined with the rapid scan speeds of modern instruments, Fourier-transform infrared (FT-IR) spectroscopy provides a powerful real-time method for monitoring chemical changes (for example, the optical adhesive caused by illumination of a UV lamp). This article describes the characterization of several adhesives used in an optical assembly. Several different approaches to measuring the rate of change during the curing experiment are described. As the number of uses for UV curing and photopolymerization increases, real-time FT-IR should play a major role in characterizing these new materials and products.

Process analytical technology (PAT) and hot-melt extrusion (HME), commonplace in the food and polymer industries, are becoming increasingly deployed in the pharmaceutical industry. Herein the application of in-line, transmission mode, Fourier-transform near-infrared (FT-NIR) spectroscopy to the HME manufacturing platform for a drug product in development is detailed. NIR spectroscopy and partial least squares (PLS) models were developed for real-time active pharmaceutical ingredient (API) loading (%wt/wt) and surfactant loading predictions. These predictions were used for fault detection, isolation of suspect material, and real-time troubleshooting during HME. Additionally, the NIR/PLS output was used for real-time release of the intermediate drug product.

In recent years, attenuated total reflection (ATR) spectroscopy has become the preferred method for many routine infrared (IR) measurements. However, the simplicity of the technique has made it available to users who may not be aware of some effects that significantly influence the appearance of ATR spectra. This results in changes to the relative intensities of different absorption bands. The aim of this article is to explain the origin of these effects and to provide examples. In particular, it will focus on those effects that are not evident from inspection of the spectra.

Liquid chromatography–mid infrared spectroscopy (LC-IR) is a powerful tool for copolymer analysis. This article describes an automated, self-regulating solvent-removal interface that produces continuous transmission spectra from the deposited, solvent-free, solid-phase chromatogram.

Simulated leaf spectral data were generated to analyze scattering impact and then compared to experimental data to validate the conclusions of the simulation.

Algae and other aquatic species are promising sources for biomass that can be economically converted into fuel, and several infrared sampling techniques can be used to analyze these samples.

In the last four columns we described the theory of what should happen when we perform classical least squares calculations on mixtures when Beer's law applies. In this column we take our first look at what actually does happen.

The wavelet packet transform (WPT) combined with the modified uninformative variable elimination (MUVE) method (WPT–MUVE) is proposed to select variables for multivariate calibration of spectral data.

Combining multiple sensors into one instrument increases the probability of detecting explosive residues and enables the detection of a greater number of explosives.

A review of recent developments in MIR spectroscopy that have potential for field deployment in defense and homeland security applications for standoff detection of highly energetic materials (HEM) and homemade explosives (HME), as well as in forensic sciences applications.

Fourier transform infrared (FT-IR) spectrometers provide spectra in less time than scanning systems, but water vapor and/or CO2 in the sample chamber leads to additional peaks that may obscure important information. These interferences can be eliminated by sealing the sample chamber and purging with dry, CO2 free air (purge gas) or nitrogen for a short period of time.

Attenuated total internal reflection Fourier-transform infrared imaging confirms the presence of drug components in illicit tablets.

Fat and other nutritional values can easily be determined by NIR analysis. However a proper sample preparation beforehand is essential for a correct result.