Infrared (IR) Spectroscopy

Measurements of the optical proper ties of a ceramic material, Z93, which is in current use on the International Space Station (ISS), reveal why this material is successful for thermal control in the ISS implementation, and also point to potential future material design improvements.

Spectroscopic ellipsometry, correlated with UV-vis-NIR spectroscopy, is used to determine the optical constants of thin films, such as in GexSb40-xSe60 chalcogenide glass.

Portable spectroscopic instruments have not had significant visibility within the scientific community compared with, for instance, the current generation of high-performance laboratory mass spectrometers.

In celebration of Spectroscopy’s 35th Anniversary, leading spectroscopists discuss important issues and challenges in analytical spectroscopy.

Here, we continue our examination of the infrared (IR) spectra of organic nitrogen compounds with imides, which are a common chemical intermediate. IR can be used not only to identify imides, but also to distinguish between straight chain and cyclic imides. We explain how.

The N-H stretching and bending peaks can be used to distinguish primary, secondary, and tertiary amides and to ascertain protein structure. Here’s how.

Amides are an important functional group found extensively in polymers and proteins. There are three different families of amides. Here, is explained how to distinguish them using infrared spectroscopy.

Analysis of FDA Form 483 observations and warning letters for infrared spectrometers reveals a range of data integrity problems and a lack of laboratory procedures for the technique. Is your laboratory in the same situation?

The amine salt functional group contains ionic bonding, and is extremely polar, giving rise to a number of intense and uniquely placed peaks that are easy to identify for primary, secondary, and ter tiary amines.

Nitriles are easy to spot because of the unusual intensity and position of the C≡N stretching peak.

Significant progress is being made to harness the power of spectroscopy technique for medical research. An ongoing challenge, and area of development, in this effort, is to “see” more and more detail about biological activity, even within individual cells. Ji-Xin Cheng, a professor of biomedical engineering at Boston University, is advancing such work, by developing techniques like midinfrared photothermal (MIP) imaging and Raman spectromicroscopy. Cheng is the 2019 winner of the Ellis R. Lippincott Award, which is awarded annually by the Optical Society, the Coblentz Society, and the Society for Applied Spectroscopy, to an individual who has made significant contributions to the field of vibrational spectroscopy. Here, Cheng speaks to us about those techniques.

Our annual review of products introduced at Pittcon or during the previous year

A detailed guide to interpreting the infrared spectra of organic nitrogen compounds, including secondary and tertiary amines.

Portable NIR spectroscopy is demonstrated as a rapid and mobile analysis method for authenticating cardiovascular medicines in critical situations, and to indicate whether formulations are counterfeit or substandard.

Aromatic esters follow the ester Rule of Three, but each of these three peak positions is different for saturated and aromatic esters, which makes them easy to distinguish. Organic carbonates are structurally similar to esters and follow their own Rule of Three.

Esters are a common and economically important functional group made by reacting an alcohol and a carboxylic acid.

Carboxylates are made by reacting carboxylic acids with strong bases such as inorganic hydroxides. Carboxylates contain two unique carbon–oxygen “bond and half” linkages that coordinate with a metal ion to give two strong infrared peaks, which make them easy to see.

Acid anhydrides are unique in that they have two carbonyl groups in them. The intensity and position of their IR peaks can be used to determine which of the four types of anhydride exist in a sample.

How to spot carboxylic acids in your IR spectra

Aldehydes feature a unique “lone hydrogen” atom, giving rise to unique C-H stretching and bending peaks, making them easy to spot. In this installment, a new feature is also presented, “IR Spectral Interpretation Review,” where key concepts from past columns are presented for those new to the column and for readers who need a refresher.

An introduction to the IR spectroscopy of the carbonyl group, exploring why the peak is intense and showing how to apply that knowledge to the analysis of the spectra of ketones

In forensic science, the detection of blood on fabric is a very useful tool. Therefore, it is important that the methods used for detecting blood be as accurate as possible. Michael L. Myrick and Stephen L. Morgan, both professors in the Department of Chemistry and Biochemistry at the University of South Carolina, have been investigating the use of infrared (IR) spectroscopy for this purpose, including comparing the effectiveness of infrared diffuse reflectance versus attenuated total reflectance Fourier-transform IR (ATR FT-IR). They recently spoke to Spectroscopy about their recent studies and the critical questions they have been addressing in how IR spectroscopy is used in forensic science.

This work shows that methods based on miniaturized near- and mid-infrared spectroscopy can be used effectively for the quality control of herbal medicines.

Microplastics from clothing, abrasive action on plastics, or engineered microbeads as found in some exfoliating cosmetics are showing up in many environmental systems. FT-IR microscopy is a useful tool in the analysis of microplastics, providing visual information, particle counts, and particle identification.

Naoto Nagai focuses on solving problems for industry. In this interview, he explains his research to determine the cause of resin cracks in polyoxymethylene mold plates using IR spectroscopy.

Two unrelated discussions are presented: carbohydrates and alkynes.

Coherent two-dimensional infrared spectroscopy (2D IR) uses a series of IR femtosecond laser pulses to pump and then probe the response of a system, making it possible to learn much more about the structure and dynamics of molecules than can be seen with one-dimensional IR spectroscopy. The technique’s inventor, Martin T. Zanni of the University of Wisconsin-Madison, discussed 2D IR in a 2013 interview in Spectroscopy (1). Since 2013, Zanni has applied 2D IR spectroscopy to new systems and has started a company, PhaseTech Spectroscopy, Inc., to commercialize the technique.

We will discuss three different types of ether, which are characterized by the type of carbons attached to the central oxygen.

In addition to primary alcohols there exist secondary and tertiary alcohols.

We now turn our attention to the C-O bond, how to detect its presence in a sample from an infrared (IR) spectrum, and a study of the functional groups that contain this bond. In this first installment on the topic, we study the spectra of alcohols and learn to distinguish primary, secondary, and tertiary alcohols from each other based on their infrared spectra.