Infrared (IR) Spectroscopy

Identity testing is used in the pharmaceutical, food, and dietary supplement industries (amongst others) to ensure raw materials and final products have the correct chemical composition by answering the spectral question: Are these two samples the same? The first part of this installment instructs readers on the correct way to perform identity testing. The interpretation portion of the installment wraps up our discussion of straight chain alkanes by discussing how to determine chain length from infrared spectra. We also go over the answer to the problem from the last installment.

Multiple angle incidence resolution spectroscopy (MAIRS) has proven useful for characterization of the in-plane (IP) and out of plane (OP) vibrations of thin films on solid substrates. The MAIRS technique computes the IP and OP spectra by performing a regression analysis on a series of oblique-incidence transmission spectra collected over a range of angles of a single thin film sample mounted on a transparent substrate. MAIRS replaces the more traditional technique of the collection of a transmission spectrum of a thin film on a transparent substrate, followed by collection of a reflection absorption spectrum of the same film on a metallic substrate. Often times, preparation of the same thin film on different substrates with different chemical and physical properties can be problematic. This paper will discuss details of the electromagnetic theory of MAIRS, and demonstrate its use in producing the IP and OP spectra of several thin film samples.

In recent years there has been increased use of silicones in medicine, especially for medicinal implants. Quality control of intracorporeal-used silicones is an important task for ensuring patients’ health, but it is also a challenging one. The traditional mechanical methods used for the quality control of these silicone products, like rheometric measurements, tend to waste a lot of raw material. In this study, near-infrared spectroscopy (NIRS) has been used to replace the traditional method (rheometric measurements of control samples) using rheometry only as reference method to generate different calibration models. The applicability of NIRS as non-invasive analysis method is proven and the developed calibration models for curing processes of a silicone-adhesive at different temperatures are shown.

A huge amount of information is contained in the FTIR spectra of soils in the mid infrared (MIR) region (4000 to 400 cm-1). The spectra provide an overall chemical profile of the soil, encompassing fundamental vibrations of both the organic and mineral components. Interpretation of the spectrum of individual soils can provide a powerful means of differentiating between samples and therefore has considerable potential for use in forensic applications, and indeed we have successfully used laboratory-based FTIR analysis of soil to provide evidence in forensic casework. In recent years handheld FTIR spectrometers have become available and this makes it possible for in situ or field-based FTIR analysis of soils at a crime scene. However, reliable and tested protocols are not yet available for field-based FTIR analysis of soil. This paper discusses the sampling options for field-based FTIR of soil and describes tests of the methodology we are developing, for a handheld FTIR, on soil samples tested in the context of a mock crime scene.

In honor of Spectroscopy’s celebration of 30 years covering the latest developments in materials analysis, we asked experts to assess the current state of the art of six key spectroscopic techniques. Here, the experts weigh in on what they considered the most important recent advances in infrared (IR) spectroscopy.

Continuing the theory and practice themes from previous columns, the theory portion of this column will be a discussion of the proper way of handling the infrared spectral interpretation of mixtures. In my opinion, mixtures are the biggest obstacle to interpreting infrared spectra, and I will share with readers five tried-and-true techniques for dealing with them. The practice portion of the column will give the answer to the last installment’s problem, and complete the spectral analysis of straight chain alkanes.

In honor of Spectroscopy's celebration of 30 years covering the latest developments in materials analysis, we asked a panel of experts to assess the current state of the art of infrared (IR) spectroscopy and to try to predict how the technology will develop in the future.

Interpreting infrared spectra is fun, but to do it properly one must be grounded in theory, which might be not so enjoyable for some. To cover theory and interpretation judiciously, this installment (and the next several installments) will begin with a section on theory and end with coverage of interpreting spectra. Here, we introduce the theory behind light and spectral units and the interpretation of methyl and methylene groups contained in straight alkane chains.

There is a continuing need for Fourier transform infrared (FT-IR) users to receive training in how to interpret the infrared spectra they measure. This new column will provide practical advice about how to do this. This first installment will present why this type of column is important, discuss some basic IR theory, and lay out a blueprint for future installments.

Macro attenuated total reflection FT-IR spectroscopic imaging is a powerful and underutilized tool. This article presents an overview of approaches and opportunities for using this method to study dynamic processes such as diffusion, sorption, crystallization, and dissolution.

When images are measured in reflectance, the observed structure is not necessarily just that of the sample surface.

What if the decisions neurosurgeons make during surgery - such as about how much tissue to remove - could be guided by immediate results from spectroscopic methods? A number of spectroscopy researchers are seeking to advance methods to make that both possible and practical.

Law enforcement relies upon "schedules" or lists of controlled substances. In an attempt to circumvent the law, clandestine laboratories produce synthetic designer drugs that are chemically related to a controlled substance, but are different enough to raise legal issues with prosecution.

Counterfeit and illicit tobacco may contain potentially toxic organic impurities that result in adverse health effects to the consumer. The aim of this work was to investigate the feasibility of the identification of organic impurities in counterfeit or illicit tobacco using attenuated total reflectance-Fourier transform infrared (ATR-FT-IR) spectroscopy.

The mechanical properties of polymer films such as tensile strength and resistance to tearing depend strongly on the orientation of the polymer chains. Fourier transform infrared (FT-IR) spectroscopy can be used to measure the degree of orientation both within the plane of the film and normal to it.

Resonance-enhanced atomic force microscopy (AFM)–infrared (IR) is a new technique that couples an atomic force microscope with a pulsed tunable IR laser source to provide high spatial resolution chemical analysis of samples as thin as a monolayer. The AFM probe tip acts as a small local detector of the thermal expansion of the sample caused by the absorption of the monochromatic IR radiation.

What if the decisions neurosurgeons make during surgery - such as about how much tissue to remove - could be guided by immediate results from spectroscopic methods? A number of spectroscopy researchers are seeking to advance methods to make that both possible and practical. One such researcher is Allison Stelling, who recently completed her PhD under Professor Peter Tonge at Stony Brook University in New York. Stelling is currently at the Center for Materials Genomics at Duke University, in Durham, North Carolina, working under Professor Stefano Curtarolo.

An interview with Allison Stelling, a recent PhD from Prof. Peter Tonge's group at Stony Brook University in New York, exploring the use of IR spectroscopy for use in intraoperative diagnostics during brain surgery.

In these types of IR imaging, various factors contribute to the observed resolution. These factors are illustrated with images of materials with known structures.

Highlights of recent advances in three major areas of molecular spectroscopy: infrared (IR), Raman, and fluorescence.

Everyone loves a list, and the editors of Spectroscopy are no exception! In 2013, Spectroscopy covered a wide array of topics throughout the year to bring you the most relevant information for your work, on topics ranging from selecting the right ICP-MS system to deciding which Raman technique is right for you, from our annual salary survey to calibration transfer. Here is a list of 13 popular articles and columns from 2013

In a recent interview, Rohit Bhargava, winner of the 2013 Craver Award from the Coblentz Society, discusses current trends in IR spectroscopic imaging, including application-specific instrumentation, improvements in data interpretation, and identifying relationships between structure and spectra.

Click here to view the complete Wavelength newsletter from October 15, 2013.

Fourier transform infrared (FT-IR) spectroscopy has been used to identify unknown materials, determine the quality or consistency of a sample, and determine the amount of components in a mixture. Gary Small, of the Department of Chemistry and Optical Science and Technology Center at the University of Iowa, spoke to Spectroscopy about his work using passive FT-IR remote sensing measurements.

A novel infrared-based method that permits fast and impartial analysis of detergent removal from biological samples is presented.