Gloria M. Story

Attenuated Total Internal Reflection Infrared Mapping Microspectroscopy Using an Imaging Microscope

Attenuated total internal reflection (ATR) infrared mapping microspectroscopy using an infrared microscope and a focal plane array is investigated and reported. The study demonstrates the advantages of conducting ATR microspectroscopy using a focal plane array detector. These benefits include the rapid acquisition of molecular specific images, ease of sample preparation, and increased spatial resolution. An experimental determination of the spatial resolution found that the combined system operates very close to the diffraction limit, and a 4 magnification factor associated with the germanium internal reflection element was realized. Experiments conducted on several polymer samples and a biological sample demonstrate the future viability of the method.

Pressure-induced transitions of polyethylene studied by two-dimensional infrared correlation spectroscopy

Abstract Two-dimensional infrared (2D IR) correlation spectroscopy was applied to a semicrystalline linear low density polyethylene (LLDPE) sample under varying pressure. A substantial level of spectral changes are observed when even a moderate amount of pressure is applied to the polyethylene sample. Fine features of the spectral changes are readily analyzed by the 2D correlation method. The pressure-induced 2D IR spectra indicate the observed changes in IR spectra may be attributed to the morphological reorganizations of semicrystalline superstructure of polyethylene, e.g., reorientation of lamellae and partial melting under compression.

Infrared Microspectroscopic Imaging Using a Large Radius Germanium Internal Reflection Element and a Focal Plane Array Detector

Previously, we established the ability to collect infrared microspectroscopic images of large areas using a large radius hemisphere internal reflection element (IRE) with both a single point and a linear array detector. In this paper, preliminary work in applying this same method to a focal plane array (FPA) infrared imaging system is demonstrated. Mosaic tile imaging using a large radius germanium hemispherical IRE on a FPA Fourier transform infrared microscope imaging system can be used to image samples nearly 1.5 mm × 2 mm in size. A polymer film with a metal mask is imaged using this method for comparison to previous work. Images of hair and skin samples are presented, highlighting the complexity of this method. Comparisons are made between the linear array and FPA methods.

Prism-Based Infrared Spectrographs Using Modern-Day Detectors

A comparison of prism-based spectrographs to grating-based spectrographs is made when each of the systems is coupled to a modern-day liquid-nitrogen-cooled photovoltaic array detector. A comparison of the systems is also made using a room-temperature microbolometer array detector. Finally, infrared microspectroscopy of samples whose size is ∼10 micrometers will be demonstrated using a prism spectrograph outfitted with both types of detectors. The results of the study show that prism-based spectrographs offer an economical alternative to grating-based systems when spectral coverage is more critical than spectral resolution. The results also demonstrate that spectra with good signal-to-noise ratios can be collected on any of the systems with a total integration time of 10 seconds or less.

Rapid Molecular Imaging Using Attenuated Total Internal Reflection Planar Array Infrared Spectroscopy for the Analysis of Counterfeit Pharmaceutical Tablets

A planar array infrared (PA-IR) spectrograph containing an attenuated total internal reflection (ATR) accessory has been constructed in order to permit rapid analysis of poorly transmitting materials. The technique has been optimized to allow molecular spectroscopic information to be collected in roughly 2 seconds with a corresponding peak-to-peak noise value as low as 2.14 × 10−4 absorbance units. Additionally, up to 150 spectra could be extracted from sample sizes as large as 6 mm where each spatial element measured 40 × 200 μm at the sample position. An application study for this technique entailed developing an embedding method that allows cross-sectioned pharmaceutical tablets to be brought into intimate contact with the internal reflection element (IRE) of the accessory. A supplemental investigation involved calculating the yield strength of multiple IRE materials in order to determine the maximum amount of pressure that can be applied to a sample without damaging the IRE. Finally, feasibility was demonstrated for using the instrument/accessory as a means to rapidly authenticate suspected counterfeit pharmaceutical tablets.

Phase correction and two-dimensional correlation analysis for depth-profiling photoacoustic step-scan FTIR spectroscopy

A method is described which corrects for the instrument response function in step-scan FT-IR photoacoustic spectroscopy (PAS) without distorting the thermal response information necessary for depth profiling layered samples. The instrumental phase correction functions are determined from the phase-sensitive photoacoustic signals of a strong surface absorber, such as carbon black. Phase correction functions generated from the monosignate spectrum of carbon black are used to compute the in-phase and quadrature interferograms of the sample. This treatment allows unratioed PAS spectra to properly change sign as a function of lock-in amplifier phase angle, thereby making a 2D correlation analysis of the results meaningful. This approach is used to clearly separate individual signals originating from a three-layer sample film of polydimethylsiloxane (PDMS), polyethylene (PE), and polystyrene (PS).

A method for analysis of clinical tissue samples using FTIR microspectroscopic imaging

During the past decade, Fourier transform infrared (FT-IR) microspectroscopy has been used successfully in many studies to differentiate normal and diseased tissue samples obtained from a variety of organs, including colon, cervix, prostate, and breast [1-4]. In most cases, spectra were collected for a select area of a tissue or IR images were constructed by collecting spectra point-by-point using a mapping stage on an FTIR microscope equipped with a single-element detector. Recently, a new technique has been developed for performing vibrational spectroscopic imaging microscopy using a liquid-nitrogen-cooled focal-plane array (FPA) detector and a step-scanning FT-IR spectrometer coupled to a refractive microscope [5]. With this configuration, equipped with a new 64-pixel x 64-pixel Mercury-Cadmium-Telluride (MCT) FPA detector, it has now become possible to image an 800-um × 800-um area of a specimen without moving the sample.

Mining the Information Content Buried in Infrared and Near-Infrared Band Shapes by Temporal, Spatial, and Other Perturbations

CURTIS MARCOTT LIGHT LIGHT SOLUTIONS, LLC, P.O. BOX 81486 ATHENS, GEORGIA 30608-1486 GLORIA M. STORY, ANTHONY E. DOWREY, JEFFREY T. GROTHAUS, DAVID C. OERTEL THE PROCTER & GAMBLE COMPANY MASON BUSINESS CENTER, 8700 MASON-MONTGOMERY ROAD MASON, OHIO 45040 ISAO NODA THE PROCTER & GAMBLE COMPANY 8611 BECKETT ROAD WEST CHESTER, OHIO 45069 ELI MARGALITH, LAM NGUYEN OPOTEK, INC. 2233 FARADAY AVE., SUITE E CARLSBAD, CALIFORNIA 92008

Infrared microspectroscopy using prism-based spectrographs and focal plane array detection.

Several prism-based spectrographs employing a mercury cadmium telluride (MCT) focal plane array detector have been interfaced to an infrared microscope. In the combined system, the area-defining aperture of the microscope also served as the entrance slit to the spectrograph. This investigation considered the fundamental limits of diffraction for both the spectrograph and microscope in order to determine both the spatial and spectral resolution of the system as a whole. Experimental results for spectral resolution, spectral range, and peak-to-peak noise have been presented. Finally, the dynamic capabilities of one spectrograph/microscope combination were investigated.

Pressure-modulation dynamic attenuated-total-reflectance (ATR) FT-IR spectroscopy

A single-reflectance attenuated-total-reflectance (ATR) accessory with a diamond internal-reflection element was modified by the addition of a piezoelectric transducer. Initial dynamic pressure-modulation experiments have been performed in the sample compartment of a step-scanning FT-IR spectrometer. A sinusoidal pressure modulation applied to samples of isotactic polypropylene and linear low density polyethylene resulted in dynamic responses which appear to be similar to those observed in previous dynamic 2D IR experiments. Preliminary pressure-modulation dynamic ATR results are also reported for a styrene-butadiene-styrene triblock copolymer. The new method has the advantages that a much wider variety of sample types and geometries can be studied and less sample preparation is required. Dynamic 2D IR experiments carried out by ATR no longer require thin films of large area and sufficient strength to withstand the dynamic strain applied by a rheometer. The ability to obtain dynamic IR spectroscopic infor...