Infrared (IR) Spectroscopy

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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.

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 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.

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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.

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.

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.

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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.

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.