Russian physicists suggest a technique for quick and accurate comparison of any medication with is chemical etalon.

Checking whether a pharmaceutical agent has the same content as an etalon is a burning and a complicated problem. Measuring concentration of an active compound is a piece of cake, because in this case you know what you are looking for. However, estimating content of various admixtures is much more difficult, because you do not known what admixtures are in this medication.

Scientists from Lebedev Institute of Physics suggest a simple and elegant solution for the abovementioned problem. An experimental test for possible contamination was performed on an aqueous solution of aminocapronic acid. The sample of the acid could have contained unknown admixtures, and that was why traditional chemical means of analysis could have required many time- and labour-consuming measurements.

As an alternative to traditional methods, Russian scientists have used Raman scattering technique, based upon inelastic light scattering. When a monochromatic light falls on any substance – gas, liquid or solid body, scattered light contains additional radiation with frequency, different form that of falling light. Frequency of this additional radiation is called scattered radiation frequency and a sum (or a difference) of radiation frequency of excitation laser and natural frequency of an environment studied.

 

 

Raman scattering spectrum is strictly specific for any individual substance – like a “fingerprint”. That is why Raman scattering is a convenient and effective technique for identification of various substances, research and control of chemical reactions and technological processes.

Analysis is this case is performed in the following way: object of the analysis is irradiated with a monochromatic radiation of a laser; an optical system collects radiation, scattered by a sample and sends it to a monochromator or a spectrometer for further analysis. Using optical microscope for analysis by means of Raman scattering allows studying objects with surface spatial resolution of up to 1 micron. A microscope’s lens directs light on a sample and collects scattered light for analysis.

A substance can be identified, when scientists know a Raman scattering spectrum of an etalon substance, otherwise additional studies are required. However, in case of molecular analysis Raman scattering has important advantages over other analysis techniques. Biological molecules usually consist of structural components – chains, benzene rings, hydrogen bonds and etc. Each structural component has its own vibration patterns, which give characteristic bands in Raman spectrum.

Information on molecular structure of an admixture helps significantly reduce amount of “suspects”. Tested aqueous solution of aminocapronic acid appeared to contain admixtures with naphthenes and benzene rings in their structure.

So-called Raman scattering of light was independently discovered in 1928 by Indian scientists Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan in liquids and by Soviet physicists Grigory Landsberg and Leonid Mandelstam in crystals.