John A. Reffner

Fourier transform infrared microscopical analysis with synchrotron radiation: The microscope optics and system performance (invited)

When a Fourier transform infrared microspectrometer was first interfaced with the National Synchrotron Light Source in September 1993, there was an instant realization that the performance at the diffraction limit had increased 40–100 times. The synchrotron source transformed the IR microspectrometer into a true IR microprobe, providing high‐quality IR spectra for probe diameters at the diffraction limit. The combination of IR microspectroscopy and synchrotron radiation provides a powerful new tool for molecular spectroscopy. The ability to perform IR microspectroscopy with synchrotron radiation is still under development at Brookhaven National Laboratory, but several initial studies have been completed that demonstrate the broad‐ranging applications of this technology and its potential for materials characterization.

Infrared spectroscopy of a single cell: the human erythrocyte

Methods for obtaining the infrared spectrum of a single erythrocyte by infrared microscopy have been developed. The spectrum contains the amide I, II, and III bands characteristic of protein secondary structure near 1650, 1550, and 1300 cm-1, respectively. Bound carbon monoxide exhibits a readily measured band at 1951 cm-1 for 12C16O and 1907 cm-1 for 13C16O. Both amide and CO bands are similar to those found for purified hemoglobin A. Spectra can be obtained in H2O or D2O media under physiologically relevant conditions. Single cell infrared spectroscopy (SCIR) permits the qualitative and quantitative determination of differences among individual red cells. These results suggest many potential applications for SCIR for the measurements of properties of individual cells at the molecular level under physiologically relevant conditions.

Synchrotron Infrared Confocal Microspectroscopical Detection of Heterogeneity within Chemically Modified Single Starch Granules

This reports the first detection of chemical heterogeneity in octenyl succinic anhydride modified single starch granules using a Fourier transform infrared (FT-IR) microspectroscopical technique that combines diffraction-limited infrared microspectroscopy with a step size that is less than the mask projected spot size focused on the plane of the sample. The high spatial resolution was achieved with the combination of the application of a synchrotron infrared source and the confocal image plane masking system of the double-pass single-mask Continuμm® infrared microscope. Starch from grains such as corn and wheat exists in granules. The size of the granules depends on the plant producing the starch. Granules used in this study typically had a median size of 15 μm. In the production of modified starch, an acid anhydride typically is reacted with OH groups of the starch polymer. The resulting esterification adds the ester carbonyl (1723 cm−1) organic functional group to the polymer and the hydrocarbon chain of the ester contributes to the CH2 stretching vibration to enhance the intensity of the 2927 cm−1 band. Detection of the relative modifying population on a single granule was accomplished by ratioing the baseline adjusted peak area of the carbonyl functional group to that of a carbohydrate band. By stepping a confocally defined infrared beam as small as 5 μm × 5 μm across a starch granule 1 μm at a time in both the x and y directions, the heterogeneity is detected with the highest possible spatial resolution.

Comparison of transmission and internal reflection infrared spectra of cocaine.

Comparing the infrared transmission spectrum of cocaine HCl to its attenuated total reflection (ATR) spectrum has raised questions about the use of ATR spectra for forensic drug analysis. Whenever infrared spectra are collected using different modes or sample preparation methods, small variations in peak intensity ratios or peak positions are possible. These variations in infrared spectra are small and do not interfere with qualitative analysis, but they can cause confusion when unrecognized as normal effects of the different spectroscopic techniques. Comparison of the absorption and ATR spectra of cocaine hydrochloride illustrates the type of differences that can be expected. These differences are explained by the fundamental differences in the collection techniques. For the best quantitative results, only spectra collected by the same technique should be compared.

SINGLE FIBER ANALYSIS BY INTERNAL REFLECTION INFRARED MICROSPECTROSCOPY

Attenuated total reflection (ATR) is a convenient mode for single fiber analysis by infrared microspectroscopy, particularly when transmission spectra are difficult to obtain or when surface preferenced sampling is desirable. Textile finishes such as spin finishes, anti-static finishes, and permanent press finishes are revealed by ATR techniques. Bicomponent fibers may be analyzed by a combination of ATR techniques, transmission techniques, and spectral subtraction.

Forensic Classification of Polyester Fibers by Infrared Dichroic Ratio Pattern Recognition

Using a statistical analysis of infrared dichroic ratio data and fiber morphology, 32 polyester fiber samples were classified into 22 unique individual fiber groups and five paired fiber groups. This classification was based on discriminant analysis of infrared dichroic spectra, differences in fiber diameters, and variations in cross-sectional shapes. Using only the infrared dichroic data, the fibers were sorted systematically into 13 infrared groups. A model for discriminant analysis was derived and tested using 2640 infrared dichroic ratios calculated from 5280 quantitative absorbance measurements from single fiber spectra. A tentative protocol is recommended for fiber sorting. The 32 different polyester fibers that were analyzed represented five U.S. manufacturers. Because polyester fibers are the most common synthetic fibers, differentiating single fibers is important in comparisons of forensic trace evidence.

A New Method for Fiber Comparison Using Polarized Infrared Microspectroscopy

Polarized infrared (IR) microspectrometry was used to measure the changes in infrared absorption resulting from the molecular orientation of single textile fibers. Dichroic ratios were determined from single experimental fibers subjected to incremental elongation from an unstretched to a stretched condition. Similar measurements were made on commercial fibers of the same polymer with known draw ratios. These infrared spectroscopic measurements provided a direct means for comparing fibers drawn under production conditions with single fibers stretched in controlled experiments. The dichroic ratio data are indicative of the molecular orientation that occurs when fibers are drawn in the manufacturing process. Dichroic ratio data of commercial fibers can be used to monitor textile fiber quality and to compare fiber evidence in forensic investigations.

Development and Applications of Portable Gas Chromatography-Mass Spectrometry for Emergency Responders, the Military, and Law-Enforcement Organizations.

Portable gas chromatography–mass spectrometry (GC-MS) systems are being deployed for field use, and are designed with this goal in mind. Performance characteristics of instruments that are successful in the field are different from those of equivalent technologies that are successful in a laboratory setting. These field-portable systems are extending the capabilities of the field user, providing investigative leads and confirmatory identifications in real time. Many different types of users benefit from the availability of this technology including emergency responders, the military, and law-enforcement organizations. This manuscript describes performance characteristics that are important for field-portable instruments, especially field-portable GC-MS systems, and demonstrates the value of this equipment to the disciplines of explosives investigations, fire investigations, and counterfeit-drug detection. This paper describes the current state of portable GC-MS technology, including a review of the development of portable GC-MS, as well as a demonstration of the value of this capability using different examples.

Thermal analysis of polymorphism

The combined techniques of thermomicroscopy, differential scanning calorimetry (DSC), thermomicrophotometry (TMP), and micro-Fourier transform infrared spectroscopy (FTIR) are essential for the unequivocal detection of polymorphism. The polymorphism ofp-hexadecylaminobenzoic acid (HABA), a pharmaceutical intermediate, is presented to illustrate the need to use a multitechnique approach.While DSC can record thermally induced processes, it is not a specific technique and it alone cannot distinguish polymorphic transformations from other events connected with enthalpy changes. Thermomicroscopy usually provides confirmation of polymorphism by direct observation of polymorphic forms and transformations, but not all transformations result in visual changes in structure. Micro-FTIR, combined with thermomicroscopy, confirms the chemistry of these thermal changes and provides more specific information on changes in molecular structure.ZusammenfassungDie Kombination von Thermomikroskopie, DSC, Thermomikrophotometrie (TPM) und Mikro-Fouriertransform-Infrarotspektroskopie (FTIR) ist erforderlich um Polymorphie eindeutig nachzuweisen. Die Notwendigkeit der Anwendung einer Kombination von Techniken wird an Hand der Polymorphic vonp-Hexadecylaminobenzoesäure (HABA), eines pharmazeutischen Zwischenproduktes, illustriert. DSC kann zur Registrierung thermisch ausgelöster Prozesse verwendet werden, es handelt sich aber nicht um eine spezifische Technik, die allein nicht geeignet ist, polymorphe Umlagerungen von anderen mit Enthalpieveränderungen einhergehenden Vorgängen zu unterscheiden. Thermomikroskopie erbringt gewöhnlich die Bestätigung bezüglich der Polymorphie durch direkte Beobachtung der polymorphen Formen und Umwandlungen, aber nicht alle Umwandlungen führen zu visuellen Veränderungen in der Struktur. Mit Thermomikroskopie kombiniert ermöglicht die Mikro-FTIR Aussagen über die Chemie dieser thermischen Veränderungen und liefert spezifische Informationen über Veränderungen in der Molekularstruktur.РезюмеКомбинированные мет оды термомикроскопи и, дифференциальной ск анирующей калориметрии, термом икрофотометрии и микро-инфракрасной ф урые-спектроскопии я вляются ценными для однознач ного определения пол иморфизма. С целью показа необход имости использования таких комбинированных мет одов, представлен полимор физмпгексадецилами нобензойнойпгексадециламинобе нзойной кислоты, как промежут очного фармацевтиче ского препарата. Например, ДСК может ре гистрировать термич ески наведенные процессы, но не является специфической и не мо жет отделить полимор фные превращения от други х процессов, связанны х с изменением энтальп ии. Термомикроскопия обычно подтверждает полимо рфизм прямым наблюдением полимор фных форм и превращен ий, но не все превращения сопрово ждаются визуальным изменени ем структуры. Микро-ин фракрасная фурье-спектроскопия в комбинации с термомикроскопией п одтверждает химию та ких термических изменен ий и представляет бол ее специфическую инфор мацию об изменении мо лекулярной структуры.

Thermal optical analysis and differential scanning calorimetry of chemically crosslinked polyethylene

Abstract Differential scanning calorimetry (DSC) and thermal optical analysis (TOA) were applied as part of a series of characterization methods to solid chemically crosslinked polyethylene insulation. The DSC was used to study the melting and recrystallization. The ΔH of fusion has a lower value than expected. The TOA shows premelting behavior and is more sensitive to crystalline charges, on cooling, than DSC.