Methods for quantitative infrared directional-hemispherical and diffuse reflectance measurements using an FTIR and a commercial integrating sphere.

We have developed methods to measure the directional-hemispherical (ρ) and diffuse (ρd) reflectances of powders, liquids, and disks of powders and solid materials using a commercially available, matte gold-coated integrating sphere and Fourier transform infrared spectrometer. To determine how well the sphere and protocols produce quantitative reflectance data, measurements were made of three diffuse and two specular standards prepared by the National Institute of Standards and Technology (NIST), LabSphere Infragold and Spectralon standards, hand-loaded sulfur and talc powder samples, and water. Relative to the NIST measurements of the NIST standards, our directional hemispherical reflectance values are within ±4% for four of the standards and within ±7% for a low reflectance diffuse standard. For the three diffuse reflectance NIST standards, our diffuse reflectance values are within ±5% of the NIST values. For the two specular NIST standards, our diffuse reflectance values are an order of magnitude larger than those of NIST, pointing to a systematic error in the manner in which diffuse reflectance measurements are made for specular samples using our methods and sphere. Sources of uncertainty are discussed in the paper.

Identification of Uranium Minerals in Natural U-Bearing Rocks Using Infrared Reflectance Spectroscopy.

The identification of minerals, including uranium-bearing species, is often a labor-intensive process using X-ray diffraction (XRD), fluorescence, or other solid-phase or wet chemical techniques. While handheld XRD and fluorescence instruments can aid in field applications, handheld infrared (IR) reflectance spectrometers can now also be used in industrial or field environments, with rapid, nondestructive identification possible via analysis of the solid's reflectance spectrum providing information not found in other techniques. In this paper, we report the use of laboratory methods that measure the IR hemispherical reflectance of solids using an integrating sphere and have applied it to the identification of mineral mixtures (i.e., rocks), with widely varying percentages of uranium mineral content. We then apply classical least squares (CLS) and multivariate curve resolution (MCR) methods to better discriminate the minerals (along with two pure uranium chemicals U3O8 and UO2) against many common natural and anthropogenic background materials (e.g., silica sand, asphalt, calcite, K-feldspar) with good success. Ground truth as to mineral content was attained primarily by XRD. Identification is facile and specific, both for samples that are pure or are partially composed of uranium (e.g., boltwoodite, tyuyamunite, etc.) or non-uranium minerals. The characteristic IR bands generate unique (or class-specific) bands, typically arising from similar chemical moieties or functional groups in the minerals: uranyls, phosphates, silicates, etc. In some cases, the chemical groups that provide spectral discrimination in the longwave IR reflectance by generating upward-going (reststrahlen) bands can provide discrimination in the midwave and shortwave IR via downward-going absorption features, i.e., weaker overtone or combination bands arising from the same chemical moieties.

Quantitative reflectance spectra of solid powders as a function of particle size.

We have recently developed vetted methods for obtaining quantitative infrared directional-hemispherical reflectance spectra using a commercial integrating sphere. In this paper, the effects of particle size on the spectral properties are analyzed for several samples such as ammonium sulfate, calcium carbonate, and sodium sulfate as well as one organic compound, lactose. We prepared multiple size fractions for each sample and confirmed the mean sizes using optical microscopy. Most species displayed a wide range of spectral behavior depending on the mean particle size. General trends of reflectance versus particle size are observed such as increased albedo for smaller particles: for most wavelengths, the reflectivity drops with increased size, sometimes displaying a factor of 4 or more drop in reflectivity along with a loss of spectral contrast. In the longwave infrared, several species with symmetric anions or cations exhibited reststrahlen features whose amplitude was nearly invariant with particle size, at least for intermediate and large size sample fractions: that is, ≳150 µm. Trends of other types of bands (Christiansen minima, transparency features) are also investigated as well as quantitative analysis of the observed relationship between reflectance versus particle diameter.

Intensity-value corrections for integrating sphere measurements of solid samples measured behind glass.

Accurate and calibrated directional-hemispherical reflectance spectra of solids are important for both in situ and remote sensing. Many solids are in the form of powders or granules and to measure their diffuse reflectance spectra in the laboratory, it is often necessary to place the samples behind a transparent medium such as glass for the ultraviolet (UV), visible, or near-infrared spectral regions. Using both experimental methods and a simple optical model, we demonstrate that glass (fused quartz in our case) leads to artifacts in the reflectance values. We report our observations that the measured reflectance values, for both hemispherical and diffuse reflectance, are distorted by the additional reflections arising at the air-quartz and sample-quartz interfaces. The values are dependent on the sample reflectance and are offset in intensity in the hemispherical case, leading to measured values up to ~6% too high for a 2% reflectance surface, ~3.8% too high for 10% reflecting surfaces, approximately correct for 40-60% diffuse-reflecting surfaces, and ~1.5% too low for 99% reflecting Spectralon® surfaces. For the case of diffuse-only reflectance, the measured values are uniformly too low due to the polished glass, with differences of nearly 6% for a 99% reflecting matte surface. The deviations arise from the added reflections from the quartz surfaces, as verified by both theory and experiment, and depend on sphere design. Empirical correction factors were implemented into post-processing software to redress the artifact for hemispherical and diffuse reflectance data across the 300-2300 nm range.

Adapting Raman spectra from laboratory spectrometers to portable detection libraries.

Raman spectral data collected with high-resolution laboratory spectrometers are processed into a format suitable for importing as a user library on a 1064 nm DeltaNu first generation, field-deployable spectrometer prototype. The two laboratory systems used are a 1064 nm Bruker Fourier transform (FT)-Raman spectrometer and a 785 nm Kaiser dispersive spectrometer. The steps taken to adapt for device-dependent spectral resolution, wavenumber shifts between instruments, and relative intensity response are described. Effects due to the differing excitation laser wavelengths were found to be minimal, indicating--at least for the near-infrared (NIR)--that data can be ported between different systems, so long as certain measures are taken with regard to the reference and field spectra.

Chemometric analysis of multiple species of Bacillus bacterial endospores using infrared spectroscopy: discrimination to the strain level.

Previous work using infrared spectroscopy has shown potential for rapid discrimination between bacteria in either their sporulated or vegetative states, as well as between bacteria and other common interferents. For species within one physiological state, however, distinction is far more challenging, and requires chemometrics. In the current study, we have narrowed the field of study by eliminating the confounding issues of vegetative cells as well as growth media and focused on using IR spectra to distinguish only between different species all in the sporulated state. Using principal component analysis (PCA) and a classification method based upon similarity measurements, we demonstrate a successful identification rate to the species level of 85% for Bacillus spores grown and sporulated in a glucose broth medium.

The infrared spectra of Bacillus bacteria part I: vegetative Bacillus versus sporulated cells and the contributions of phospholipids to vegetative infrared spectra.

This paper highlights the distinctions between the infrared (IR) absorption spectra of vegetative versus sporulated Bacillus bacteria. It is observed that there are unique signatures clearly associated with either the sporulated or vegetative state and that vegetative cells (or cell debris) can contribute to the spore spectra. A distinct feature at approximately 1739 cm(-1) appears to be unique to vegetative cell spectra and can also be used as an indicator of vegetative cells or cell debris in the spore spectra. The data indicate that the band arises from a lipid-soluble species such as an ester or phospholipid carbonyl bond and are consistent with it being either phosphatidyl glycerol (PG) or phosphatidylethanolamine (PE), two major classes of phospholipids found in vegetative cells of Bacillus species. A companion work discusses bands associated with the sporulated state.

The infrared spectra of Bacillus bacteria part II: sporulated Bacillus--the effect of vegetative cells and contributions of calcium dipicolinate trihydrate, CaDP.3H2O.

Our previous paper showed that certain infrared (IR) peaks, e.g., the peak at 1739 cm(-1), are due to varying (trace) amounts of vegetative cells amongst the Bacillus spores and that these and other vegetative bands are associated with lipid-soluble compounds, likely an ester or phospholipid. This work investigates the infrared spectra of eight different sporulated Bacillus bacteria. For the endospores it is observed that peaks at 1441, 1277, and 1015 cm(-1) along with a distinct quartet of peaks at 766, 725, 701, and 659 cm(-1) are clearly associated with calcium dipicolinate trihydrate, CaDP.3H2O. It is emphasized that the spore peaks, especially the quartet, arise from the calcium dipicolinate trihydrate and not from dipicolinic acid or other dipicolinate hydrate salts. The CaDP.3H2O infrared peaks and the effects of hydration are studied using quantum chemistry in the PQS software package. The quartet is associated with many modes including contributions from the Ca2+ counterion and hydration waters including Ca-O-H bends, H2O-Ca-O torsions, and O-C-O bends. The 1441 and 1015 cm(-1) modes are planar pyridine modes with the 1441 cm(-1) mode primarily a ring C-N stretch and the 1015 cm(-1) mode primarily a ring C-C stretch.

Chemical and physical characteristics of cellulose insulation particulates, and evaluation of potential acute pulmonary toxicity.

BACKGROUND: During installation of cellulose insulation (CI) in new and older houses, significant quantities of airborne material are generated. This study characterized the chemical and physical properties, and potential acute pulmonary toxicity of CI. METHODS: CI from four manufacturers was analyzed for inorganic additives and trace element impurities. Aerosols were generated and size fractionated. The number and size of fibrous and nonfibrous particles in the respirable fractions were determined. Respirable CI particulates were intratracheally instilled in rats (5 mg/kg) to evaluate potential pulmonary toxicity. RESULTS: CI samples were similar in composition with small differences due primarily to fire retardants. Less than 0.1% of CI was respirable and contained few fibers. Acute exposure to CI caused transient inflammation in the lungs and increased 4-hydroxyproline. Microscopic evaluation revealed a minimal to mild, non-progressing granulomatous pneumonitis. CONCLUSIONS: Low concentrations of respirable particles were found in CI aerosols. Particles consisted primarily of fire retardants with few fibers, and caused mild pulmonary toxicity in rats.