Raman mapping of pharmaceuticals

Raman spectroscopy may be implemented through a microscope to provide fine scale axial and lateral chemical maps. The molecular structure of many drugs makes Raman spectroscopy particularly well suited to the investigation of pharmaceutical systems. Chemometric methods currently used to assess bulk Raman spectroscopic data are typically applied to Raman mapping data from pharmaceuticals; few reports exist where the spatial information inherent to a mapped dataset is used for the calculation of chemical maps. Both univariate and multivariate methods have been applied to Raman mapping data to determine the distribution of active pharmaceutical ingredients (APIs) in tablets, solid dispersions for increased solubility and controlled release devices. The ability to axially (depth) profile using Raman mapping has been used in studies of API penetration through membranes, cellular uptake of drug delivery liposomes, and initial API distribution and subsequent elution from coatings of medical devices. New instrumental developments will increase the efficiency of Raman mapping and lead to greater utilisation of Raman mapping for analyses of pharmaceutical systems. © 2011 Elsevier B.V.Articl

Characterisation of non-viable whole barley, wheat and sorghum grains using near-infrared hyperspectral data and chemometrics

Undesired germination of cereal grains diminishes process utility and economic return. Pre-germination, the term used to describe untimely germination, leads to reduced viability of a grain sample. Accurate and rapid identification of non-viable grain is necessary to reduce losses associated with pre-germination. Viability of barley, wheat and sorghum grains was investigated with near-infrared hyperspectral imaging. Principal component analyses applied to cleaned hyperspectral images were able to differentiate between viable and non-viable classes in principal component (PC) five for barley and sorghum and in PC6 for wheat. An OH stretching and deformation combination mode (1,920-1,940 nm) featured in the loading line plots of these PCs; this water-based vibrational mode was a major contributor to the viable/non-viable differentiation. Viable and non-viable classes for partial least squares-discriminant analysis (PLS-DA) were assigned from PC scores that correlated with incubation time. The PLS-DA predictions of the viable proportion correlated well with the viable proportion observed using the tetrazolium test. Partial least squares regression analysis could not be used as a source of contrast in the hyperspectral images due to sampling issues. [Figure not available: see fulltext.] © 2011 Springer-Verlag.Article in Pres

Near infrared analysis of fossil bone from the Western Cape of South Africa

The burial environment of a fossil bone may be poorly suited to long-term preservation of important chemical constituents. Studies of fossil bone chemistry consequently benefit from knowledge of burial environmental change (burial history). Several techniques have been developed to describe alteration of fossil bone, including measurements of crystallinity using infrared spectroscopy. The utility of near infrared (NIR) spectroscopy was investigated for describing the burial history of fossil bone. Spectra from large sample areas (bulk NIR) identified secondary calcite and clay within fossil bone, and were useful for distinguishing fossils from different localities. Spectra from small sample areas (hyperspectral NIR) were used to map constituents within fossil bones. Calcite and clay pervaded the internal cavities of fossil horn cores, indicating saturation with groundwater. The identification and distribution of secondary minerals is relevant for studies of taphonomic process, hence NIR is a useful supplement to existing techniques for assessing the burial history of fossil bone. © 2011 IM Publications LLP. All right reserved.Articl

Influence of grain topography on near infrared hyperspectral images

Near infrared hyperspectral imaging (NIR-HSI) allows spatially resolved spectral information to be collected without sample destruction. Although NIR-HSI is suitable for a broad range of samples, sizes and shapes, topography of a sample affects the quality of near infrared (NIR) measurements. Single whole kernels of three cereals (barley, wheat and sorghum), with varying topographic complexity, were examined using NIR-HSI. The influence of topography (sample shape and texture) on spectral variation was examined using principal component analysis (PCA) and classification gradients. The greatest source of variation for all three grain types, despite spectral preprocessing with standard normal variate (SNV) transformation, was kernel curvature. Only 1.29% (PC5), 0.59% (PC6) and 1.36% (PC5) of the spectral variation within the respective barley, wheat and sorghum image datasets was explained within the principal component (PC) associated with the chemical change of interest (loss of kernel viability). The prior PCs explained an accumulated total of 91.18%, 89.43% and 84.39% of spectral variance, and all were influenced by kernel topography. Variation in sample shape and texture relative to the chemical change of interest is an important consideration prior to the analysis of NIR-HSI data for non-flat objects. © 2011 Elsevier B.V. All rights reserved

Raman spectroscopy of fossil bioapatite - A proxy for diagenetic alteration of the oxygen isotope composition

Fossil bioapatite may yield biogeochemical signals of paleoenvironments captured by living organisms. Bioapatite may be diagenetically altered, however, with ions added or removed post-mortem; such change is typically assessed using destructive and demanding techniques. Here, Raman spectroscopy is used as a rapid and non-destructive way to identify significant diagenetic alteration of fossil bioapatite. We found spectral parameters of phosphate symmetric stretching (μ1-PO43-) to be very sensitive to variations in apatite chemistry, particularly with respect to common diagenetic components (CO32-, F-, Sr2+). The Raman spectral parameters were subsequently applied to a set of modern (biogenic) and geologic (magmatic) apatite samples as potential endmembers for diagenetic alteration. Raman spectra were also collected from enamel and dentin (respectively resistant vs. alteration-prone) of fossil teeth. Phosphate-oxygen isotopic values from the same enamel-dentin samples were used as an index of alteration and provided definition of Raman spectral parameters as relates to diagenetic alteration. Diagenetically altered samples were characterised by spectra with μ1-PO43- widths (at half maximum height) less than 13.0cm-1, and μ1-PO43- band positions greater than 964.7cm-1. Raman spectroscopy is shown to have potential as a tool for pre-screening fossil apatite samples before further analyses. © 2011 Elsevier B.V.Articl

Measurement of amorphous indomethacin stability with NIR and Raman spectroscopy

The recrystallisation of amorphous indomethacin (IMC) has been investigated using NIR and Raman spectroscopy and differential scanning calorimetry (DSC). Two methods were used to prepare the amorphous state (ball-milling, and melting and quench-cooling) and samples were stored under three sets of conditions (25 °C dry, 40 °C dry and 40 °C at 75% RH). The recrystallisation of amorphous IMC was quantified by DSC and compared to trends observed using Raman and NIR data. It was found that the multivariate analysis of Raman data agreed better with DSC data than univariate NIR or Raman analyses, or multivariate NIR analyses. The quenched-cooled samples were spiked with crystalline seeds (0 and 5%) and the rates of recrystallisation compared with ball-milled samples. It was found that the ball-milled samples rapidly recrystallised (within 20 days) but quench-cooled samples retained amorphous content for 20 days, even when spiked with γ-IMC to 5% (w/w) level. © 2011 Elsevier B.V. All rights reserved