Fran Adar

The use of Raman spectroscopy to produce material images whose contrast is derived from chemical or crystallographic species has been seen as quite useful since the introduction of the Raman microscope in 1976, but particularly, more recently, with the development of more sensitive and easier-to-use instruments. When the various species in the field of view have spectra with non-overlapping analytical bands, simple univariate analysis can provide good images. When overlapping bands are present, multivariate techniques, especially MCR (Multivariate Curve Resolution), have been successfully applied. However, there are cases where even MCR results may be problematic. We will look at some maps of a ceramic composite containing SiC, Si, B4C, and Carbon, where each of these species has non-unique spectra to see what type of results flexible software can produce. What is the goal in this type of exercise? For some of us, creating images is like a teenager’s computer game. But really what we are trying to do is to extract information about a sample from its Raman image. A beautiful rendition is nice, but it must yield information. The following will show how Raman maps can provide useful information on a sample.

This column is a mini survey of progress that has been made over the last few years in surface enhanced Raman scattering (SERS). The potential of SERS to provide signals of analytes at very low concentrations continues to beckon the analytical chemist. What the last years have produced is a body of work showing the role of the physical properties of metals, based on their geometrical and electronic properties, in enhancing the signals. As this field matures, we foresee production of surface enhancing films and particles that will provide reproducible Raman signals for applications in areas such as environmental and biomedical studies.

There is growing interest in using Raman as a spectroscopic probe of biological systems based on its high information content, its compatibility with an aqueous environment, and the spatial resolution that is consistent with physical optics (as good as ~0.5 μm).

There are multiple circumstances where characterization of a collection of particles has value to analysts. In some environments, materials are plagued by particulate contamination that impacts product quality.

Metal oxides often occur in crystals where there are no molecular units. Here, we provide an introduction to the concepts that need to be understood when analyzing metal oxides in materials such as paint, ceramic pigments, corrosion films, catalysts, and minerals.

Results of tablet matching measurements and characterization of packaging are presented.

The physics that determine how gratings and spectrographs work are summarized in simple terms for new users of Raman equipment.

The presence of electronic transitions in the visible part of the spectrum can provide enormous enhancement of Raman signals.

Here, real spectra illustrate how to be your own critic when evaluating band-fitted spectra.

The motivation for the development of an instrument for transmission Raman measurements is described. The basic instrumentation and the first results from a commercial system are provided. Transmission Raman spectroscopy (TRS) performance is compared to and contrasted with that of a confocal Raman microscope.

Columnist Fran Adar discusses applications for Raman and FT-IR spectroscopy.

Manufacturing control of pharmaceutical solids requires routine measurement of content uniformity. Because of the high information content in Raman spectra, it has been considered a candidate technology for making these measurements.

In this article, columnist Fran Adar will review the important features of the Raman spectra of these materials and indicate why the extracted information is important for material development and engineering.

Compounds of magnesium and calcium are common components of pharmaceutical formulations. Spectroscopic imaging can provide a complete understanding of a formulation. This paper compares two spectral imaging techniques — energy dispersive X-ray fluorescence (EDXRF) microscopy and Raman microscopy.

The authors discuss how the Raman microscope is being used successfully to characterize pharmaceuticals, analyze disease states, and to characterize semiconductors and nanotechnologies.