May 8th 2024
I have been writing this column for almost 10 years, and we have reached a watershed moment. We have covered what I call the beginning and intermediate topics. However, before we venture off into advanced topics, a review is in order. I will spend the next four columns summarizing what we have learned so far so that the advanced topics will make more sense.
FT-IR Microscopic Analysis of Polymer Laminate Samples Including Transmission and ATR Spectroscopy
August 1st 2016Polymer laminates typically make complex samples for infrared analysis, comprising multiple layers with defined thicknesses, in some cases less than 10 µm. When measuring extremely narrow laminate layers, the use of attenuated total reflectance (ATR) may provide improved spectra of the laminate cross-section, because ATR microscope objectives offer a greater spatial resolution than transmission due to additional magnification. This paper details the preparation of polymer laminate sample cross-sections and the collection of transmission and ATR spectra of various layers. Further analysis of the laminate spectra will also be explored utilizing a multivariate curve resolution (MCR) algorithm. An example laminate sample is examined utilizing all the tools available on a standard FT-IR microscope.
The Benzene Fingers, Part I: Overtone and Combination Bands
July 1st 2016This installment begins with a needed discussion on the theory behind the three different types of infrared bands, how to recognize them, and how to use them to help you interpret spectra. Continuing on from the last column, this knowledge is used to help better distinguish mono- and di-substituted benzene rings from each other.
Distinguishing Structural Isomers: Mono- and Disubstituted Benzene Rings
May 1st 2016Following up on the last installment, we examine the infrared spectra of mono- and di-substituted benzene rings. We will examine numerous example spectra and learn how the position of C-H wagging peaks, and the presence or absence of a ring-bending peak, allow one to distinguish between mono-, ortho-, meta-, and para-substituted rings most of the time.
Spectroscopy Announces the First Winner of the Emerging Leader in Molecular Spectroscopy Award
March 22nd 2016Matthew Baker, a senior lecturer in chemistry at the University of Strathclyde, in Glasgow, has won the inaugural Emerging Leader in Molecular Spectroscopy Award, which is sponsored by Spectroscopy magazine. This new annual award recognizes the achievements and aspirations of a talented young molecular spectroscopist, selected by an independent scientific committee. The award will be presented to Baker at the SciX 2016 conference in September, where he will give a plenary lecture and be honored in an award symposium.
Group Wavenumbers and an Introduction to the Spectroscopy of Benzene Rings
March 1st 2016Continuing our theme of investigating the infrared spectra of hydrocarbons, we look at the nature of aromatic bonding and why aromatic rings have unique structures, bonding, and infrared spectra. Then we examine, in detail, the spectra of mono- and di-substituted benzene rings, and learn that infrared spectroscopy easily distinguishes between ortho-, meta-, and para- structural isomers.
A Process for Successful Infrared Spectral Interpretation
January 1st 2016We wrap up our introduction to the theory of infrared spectral interpretation with a discussion of the correct process to follow when interpreting spectra. The author has developed this 12-step system over many years of interpreting spectra, and finds it gives him the best results. The process includes knowing how a spectrum was measured, systematically identifying peaks, and the proper use of infrared spectral interpretation aids. The answer to last column’s quiz is also disclosed.
Effect of Azimuthal Angle on Infrared Diffuse Reflection Spectra of Fabrics
Infrared spectroscopy is an appealing technique for application to forensic samples because it offers the benefits of being non-destructive and non-hazardous, fast, reasonably sensitive, and resistant to some of the interferences of many commonly used techniques. Our research team has been focusing on detecting biological fluids on fabrics, which are inherently anisotropic substrates for spectroscopy. The work presented here investigates the effect of azimuthal angle of the sample on the infrared diffuse reflection spectra of fabrics with a goal of removing sampling differences as a source of analytic variation.
Lineshapes in IR and Raman Spectroscopy: A Primer
November 1st 2015Infrared and Raman bands are typically described in terms of peak location and peak height. The shape of the peak-its form, width, and asymmetry-is less well understood. Bandshapes largely depend upon interactions between vibrating molecules and their environment. An understanding of this relationship may enhance spectral interpretation and can explain unexpected behaviors, in both qualitative and quantitative analyses. This paper presents basic concepts that influence line shapes and shows the complex lineshape changes in an apparently simple system of acetone and water.
Advancing the Application of NIR Spectroscopy
September 11th 2015Although near-infrared (NIR) spectroscopy is not a particularly sensitive technique, it can be implemented with little or no sample preparation and thus is well suited to applications such as process monitoring, materials science, and medical uses. We asked a panel of experts to comment on important current applications of NIR, as well as emerging new areas of application and the challenges involved in those newer applications.
How to Properly Compare Spectra, and Determining Alkane Chain Length From Infrared Spectra
September 1st 2015Identity 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.
Applications of Infrared Multiple Angle Incidence Resolution Spectrometry
August 1st 2015Multiple 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.
Using Near-Infrared Spectroscopy to Monitor the Curing Reaction of Silicone Adhesives
August 1st 2015In 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.
In Situ FTIR Analysis of Soils for Forensic Applications
August 1st 2015A 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.
Recent Advances in Infrared Spectroscopy
July 20th 2015In 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.
More Theory and Practice: The Thorny Problem of Mixtures and More on Straight Chain Alkanes
July 1st 2015Continuing 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.
Analysis of the State of the Art: Infrared Spectroscopy
June 1st 2015In 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.
Electromagnetic Radiation, Spectral Units, and Alkanes
April 1st 2015Interpreting 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.
IR Spectral Interpretation Workshop
January 1st 2015There 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 ATR-FT-IR Spectroscopic Imaging of Dynamic Processes
October 1st 2014Macro 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.
Using Infrared Spectroscopy for Real-Time Diagnostics During Brain Surgery
September 1st 2014What 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.
Identifying Synthetic Designer Drugs Using FT-IR, Raman, and GC–IR
August 1st 2014Law 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.
Measuring Orientation in Polymer Films
August 1st 2014The 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 Nanoscale IR Spectroscopy of Ultrathin Films and Monolayers on Metals
August 1st 2014Resonance-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.
Using Infrared Spectroscopy for Real-Time Diagnostics During Brain Surgery
June 9th 2014What 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.
Using Infrared Spectroscopy for Real-Time Diagnostics During Brain Surgery
June 1st 2014An 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.