Vibrational spectroscopy, which is a technique for revealing the chemical and physical properties of molecules, is a precious tool in the pharmaceutical sector. Researchers at the Analytical Chemistry Laboratory of the University of Liege who specialise in this area of research, regularly collaborate with pharmaceutical companies to check their raw materials, finished products and processes.

The term “vibrational spectroscopy” conjures up visions of an antiquated form of torture or perhaps even an endoscopy-like method for exploring our body cavities. Actually it is nothing of the sort: vibrational spectroscopy is a technique that provides chemical and physical information thanks to the analysis of vibrations of the matter being studied whether this involves molecules in solution or a solid. It is one of the main research subjects of the Analytical Chemistry Laboratory of the Pharmacy Department of the University of Liege directed by Professor Philippe Hubert whose research focusses on the quality of drugs from the raw materials stage to the finished product. “Three main avenues of research are pursued in the Analytical Chemistry Laboratory: the development, robust optimisation and validation of methods for analysing pharmaceutical and biological samples, chemometrics which consists of applying mathematical and statistical tools that make it possible to obtain a maximum amount of information from a large amount of data, and finally, vibrational imaging”, explains Doctor Eric Ziemons, who is a specialist in this latter field of research. “Vibrational spectroscopy has developed strongly since the beginning of the 2000s and is now very widely used in the pharmaceutical field for checking raw materials, finished products but also key stages in a process aimed at manufacturing products that conform to regulatory standards”, explains the researcher.

Vibrating the molecules in order to expose them

There are three main techniques of vibrational spectroscopy known as mid-infrared (MIR), near-infrared (NIR) and Raman. In the context Process Analytical Technology (PAT), the first is used for more specific applications and the two others are often considered as being complementary. “Near-infrared spectroscopy is a technique that is very well-developed while that based on Raman scattering that is being currently developed offers advantages with regard to the interpretation of the signals obtained. It is also a very promising technique in the biotechnology sector”, explains Eric Ziemons.  Without going into the details of these different techniques, all three are based on the same principle: causing the vibration of the molecules in a sample to vibrate and gathering information on the chemical bonds of the molecules that it is composed of. “In this way we obtain two types of information: chemical and also physical characteristics (crystalline structure, size of the particles, hardness of a tablet)”, continues the specialist. “These techniques present important advantages with regard to traditional methods such as liquid chromatography. While analysis of a drug by the latter method takes several minutes, analysis by vibrational spectroscopy only takes 5 to 10 seconds and does not require preparation of the sample beforehand. Combined with imaging, it makes it possible to precisely map one or other compounds of the pharmaceutical matrix”, indicates Eric Ziemons. Another non-negligible advantage, particularly in the context of following procedures or in the fight against drug counterfeiting: vibrational spectroscopy is a non-destructive method. The sample analysed can therefore be recovered to be subjected to other analyses.