Infrared (IR) Spectroscopy

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.

The application of FT-IR spectroscopy in quality assurance and quality control has largely been limited to laboratory efforts - bringing the samples to the instrument located on a benchtop in a lab. The advent of handheld analyzers such as A2 Technologies' Exoscan system, enables FT-IR to move from the lab to analyses at the sample site.

In the manufacturing process, it frequently becomes important to determine if metal parts are clean or are sufficiently lubricated with oil. Infrared analysis of small, flat pieces can be readily carried out by in-compartment grazing angle specular reflectance.

The connection between the mathematics of classical least squares and the graphical displays used to present it is examined in further detail.

Near-infrared spectroscopy (NIRS) is a powerful technique for rapid and nondestructive material analysis. Scientific breakthroughs over the past several decades have made NIRS one of the most powerful tools for research, especially in industries such as food and drug, chemical, oil and gas, and plastics. This technique has mainly been limited to nonportable applications due to instrument size, fragility, and cost.

Infrared analysis of seized drugs is underutilized in many forensic laboratories owing to the ambiguous results produced by samples containing a mixture of compounds. The use of a patented multi-component search algorithm can help overcome the limitations of infrared for the identification of drugs in mixture samples.

Confocal Raman imaging opened the door for many applications in Raman spectroscopy and imaging that were previously unavailable for measurement with conventional (non-confocal) Raman methods. However, high confocality always results in a high focus sensitivity and this can make measurements difficult with rough or inclined samples.

FT-IR diffuse reflectance sampling coupled with an environmental temperature chamber offers a convenient method to study sample degradation, to evaluate catalyst efficiency, and to determine reaction pathways as a function of temperature and pressure.

The authors discuss the concept of the explosive bouquet and its application to the spectroscopic detection of explosive compounds such as C4.

Diamond is generally not used as a multiple reflection ATR element due to its strong lattice bands around 2200 cm-1M.

Kidney stones are complex, biological matrices often composed of mixtures of minerals and organic matter.

FT-NIR analyzer to perform in-line determination of tablet coating thickness during spray coating.

A2 Technologies' Exoscan hand-held FTIR (Figure 1) is increasingly being used by researchers involved in the geosciences for analysis of rocks, minerals, and soil for a broad variety of applications.

Fourier transform–infrared (FT-IR) spectroscopy is convenient and effective for the analysis of foreign matter and other defect analysis. It is widely used to confirm, identify, and detect matter in many applications, including raw materials, medical products, packaging, and coatings.

Infrared (IR) spectroscopy is one of the most versatile and powerful analytical tools that we have today for the characterization and identification of materials. Its strength lies in its ability to handle a broad range of material types, in any physical state, at a wide range of concentrations, and on many occasions, with direct methods of measurement. These strengths are about to be enhanced by the use of instrumentation that utilizes a choice of broadly tunable laser devices, covering the sweet spot of the mid-IR spectrum, the "fingerprint region." These systems currently cover the spectral range of 6–12 ?m (1665–830 cm-1), which provides spectroscopic access to almost all classes of chemical compounds. This article reviews the benefits offered by such a laser system for a wide range of new and challenging applications.

Relying primarily on transmission or reflection techniques, FT-IR microscope and imaging systems often can require tedious sample preparation to obtain representative data from a sample. Conversely, similar to a sample compartment attenuated total reflectance (ATR) accessory, the ATR microscope objective requires no sample preparation as the sample can simply be contacted with the ATR element, or crystal, and then the sample spectra can be collected using the microscope detector. The ATR objectives discussed here are designed to offer simultaneous video observation of the selected sample area during infrared data collection. These ATR objectives provide a unique capability for sample observation and infrared data collection when utilizing a software mapping feature offered with the FT-IR microscopes discussed.

The most popular design of a hollow waveguide consists of silica glass tubing coated internally with silver and silver iodide to create a highly reflective surface. The external surface of the silica glass tubing is coated with an acrylate to enhance waveguide strength. In contrast to traditional mid-IR optical fibers, such as chalcogenide glass, and silver halide polycrystalline fibers, hollow waveguides offer distinct advantages for mid-IR remote sampling. Hollow waveguides, which were recently incorporated into a mid-IR sampling accessory, provide enhanced durability and span the full mid-IR range. This article details the technology and performance of hollow waveguides in the mid-IR spectral region and presents applications in remote sampling.

Establishing credibility and reliability of the information provided by a Fourier transform–infrared (FT-IR) spectrometer is paramount to mitigating risk in the QA/QC laboratory, where simple, fast and error-free analysis of unknown materials or material verification are required. To meet the demands of a modern QA/QC laboratory, FT-IR spectrometers must include capabilities that shift the burden of proving the reliability of the information away from the analyst so they can concentrate on the sample, not on verifying the integrity of the data. Recent design advances in both FT-IR spectrometer hardware and software give users greater confidence by continually reporting instrument status and performance verification, efficiently and effectively running pass–fail tests against specification, and easily adjusting to the degree of variation in a given set of products.

Characterization of trace evidence is an invaluable asset to the forensic scientist in solving crimes. In particular, the characterization needs to be specific enough so that the identification of material collected at a crime scene can be identified forcefully with material collected from a suspect's environment. Colored microscopic fibers can be discovered easily at a crime scene and collected for analysis. The question is what physical tool can be used to characterize these fibers. Fourier transform–infrared (FT-IR) spectroscopy is a well-established method for characterizing trace evidence. In this article, FT-IR, FT-Raman, and dispersive Raman spectra of a series of prepared fibers will be evaluated for their information content.