Expert View: Raman imaging and spectral database management for pharmaceutics
Sophisticated hardware and software offer speed and precision. Pharmaceutical development often involves samples in solution or on transparent substrates. For these applications, confocal Raman imaging using an inverted beam path is an especially versatile and powerful investigative method.
The entirely nondestructive technique is based on the Raman effect, in which the molecular bonds in a sample are excited with monochromatic light. The light then scatters, resulting in a specific spectrum regarded as a “fingerprint” by which different molecules can be identified. With an inverted beam path, the excitation light, usually a laser, is directed to the sample from below. This ensures that larger samples and sample holders such as Petri dishes can be accommodated and allows the use of environmental enclosures. A complete Raman spectrum is acquired at every measurement point before being compiled into an image that shows the distribution of the components. A truly confocal Raman microscope additionally delivers the information in three dimensions. These attributes are of crucial importance in pharmaceutical development. There are as many Raman spectra as there are distinct molecules. It is therefore helpful to have a database of relevant Raman signatures to compare with imaging scan results. An advanced Raman spectral database management software can execute automated matching of reference spectra with those acquired along with a demixing functionality that resolves composite spectra into constituents. One Raman imaging scan can therefore reveal the chemical identities of every individual component along with their physical distribution. Newly acquired spectra can also be entered into a custom database for future reference. The WITec alpha300 Ri inverted confocal Raman microscope combined with WITec’s TrueMatch Raman spectral database management software represents the current leading edge of nondestructive chemical characterisation. The system provides the ability to view every substance in a pharmaceutical sample in fine detail, quickly and conveniently with powerful automated routines maximising the benefits of catalogued Raman data. The streamlined workflow of the fully integrated hardware and software can greatly accelerate pharmaceutical research.