Quantitative Infrared Spectroscopy used as a tool to monitor the hydrolysis of aspirin

Rapid advances in science and medicine have led to an increase in the demand for chemical and structural information on biological and pharmacological materials. Due to its unique fingerprinting capability, vibrational spectroscopy plays a significant role in providing structural and mechanistic information through the ability that IR spectroscopy offers to identify small changes in the structure of molecules found in a sample. Advances in the field of vibrational spectroscopy across the scientific field, and in particular within pharmacology have lead to advances in the methods used for drug design and development.
Infrared (IR) spectroscopy primarily used in the chemical and physical sciences and in material development, is sensitive to intramolecular bonds, which enables the characterization of complex biological patterns rather than analyzing single monomers. The IR spectra contain information about all molecules within the analyzed medium and the method involves the “examination of the twisting, bending, rotating and vibrational motions of atoms in a molecule.” (Linde Gas, web Reference) The method is simple and cost-effective (Backhaus et al, 1998) which enables it as a prospective tool for screening procedures in the pharmaceutical field (Petrich, 2000).
The method of using the properties of such IR spectra is however, not a completely novel idea, as we have seen how IR spectroscopy is employed in repetitive analytical techniques in, for example, agricultural and process control applications (Davies, and Giangliacomo, 2000) The new clinical challenge to these applications is associated with methods which can be readily automated, to reduce the costs and handling times associated with applying such techniques, and suitable for as wide a range of pharmaceutical analyses as possible.
Infrared spectroscopy (IR spectroscopy) has been described as being important in the techniques involved in drug design, development and the study of the reactions, which they are involved in. This allows an understanding of how drugs are metabolised within the body and thus provides a valuable insight into the pharmokinetics and pharmodynamics of the drug and thus its clinical use. IR spectroscopy is primarily associated with the production of a metabolic fingerprint (Ellis and Goodacre, 2006) which is a characteristic feature of vibrational spectroscopy techniques. The production of this unique fingerprint offers the ability to identify the particular chemical product present in a sample and allows one to study the reactions it undergoes. This technique allows a rapid, non-invasive and unequivocal approach to monitoring drug reactions, which has multiple benefits to scientists and pharmacologists alike. These benefits include the alteration of particular aspects of the drug so that chemical reactions can be altered to occur at reaction rates, which are required for therapeutic intervention. Monitoring the hydrolysis of aspirin, a well-known analgesic, is one aspect of infrared spectroscopy, which is used in practice.
Quantitative Near IR analysis involve calibration of the machinery and the chemical solutions involved and this process requires the employment of sophisticated mathematical techniques. Such techniques have reached extensive use only recently with the advent of microcomputing and chemometrics. Despite the initial reluctance, NIR spectroscopy has aroused great interest in the last few years as a result of both instrumental breakthroughs (e.g., improved detectors, the development of fast-scan and Fourier transform instruments to replace filter instruments, the widespread use of fibre-optic probes and instruments for recording spectra of individual tablets, which minimize or avoid sample pre-treatment) and the incorporation into equipment-bundled software of mathematical procedures for processing NIR spectra. Near IR spectroscopy allows the chemical composition and physical properties and reactions occurring in the hydrolysis of aspirin to be determined with unique preciseness through mathematical treatments on the complex signals produced by the in the IR spectra. (Drennen and Lodder, 1990)
Fourier Transform (FT) IR spectroscopy is another type of IR technology applied to pharmaceutical analysis. (Bouhsain et al, 1996) FTIR had been traditionally used to obtain qualitative information of organic sample however more recently it has been demonstrated that FTIR spectroscopy is also a very useful tool for use obtaining accurate quantitative results from spectra obtained in a variety of different states, including solid, liquid and gaseous states. The technique is utilized in practice in spite of the general problems, which are encountered when using traditional systems of IR measurements. This is useful to observing the reactions occurring when aspirin hydrolyses, as among the problems, which remain for general applicability of FTIR spectroscopy for quantitative analysis, are the solvent and window material transparencies.
Despite the fact that IR spectroscopy is employed, UV spectroscopy is also used however, the use of flow cells for handling appropriate solvents which are used are often required in order to increase the ability to interpret the information produced in the spectra. The development of FA procedures in the field of IR spectrometry has solved some of the many drawbacks of quantitative determination and have increased the repeatability and accuracy of the determinations the possibility of direct analysis of real samples has been enhanced easy and fast methods for the quantitative quality control of several compounds in the same sample have been provided and the sensitivity of FTIR determination has been increased by means of on-line coupling with concentration techniques. The analysis of reactions occurring during the hydrolysis of the analgesic aspirin can be quantified by the combination of FIA/FTIIR.
Hence, it has been shown how it is possible to obtain information regarding specific molecular and mechanistic interactions and structure through the use of vibrational Infrared imaging technique, which will have major implications in pharmaceutical research and practice.