38 PROCESSING TECHNOLOGY
Chemical analysis of crystal growth uses infra-red technique
A team of scientists and engineers in northern England have developed an infra-red based technique that gives real time details about the chemical processes at work as crystallisation occurs.
Une équipe de scientifiques et d’ingénieurs du nord de l’Angleterre a mis au point une technique basée sur l’infrarouge qui donne des détails en temps réel sur les processus chimiques qui interviennent tandis que la cristallisation s’opère.
Ein Team aus Wissenschaftlern und Ingenieuren in Nordengland hat ein Infrarotverfahren entwickelt, das über chemische Prozesse während einer
Kristallisation in Echtzeit Aufschluss gibt.
T
he creation of reproducible crystallisation processes has long been a fundamental challenge for drug manufacturers. However, help is
now at hand with a new technique developed by engineers at the University of Leeds in England that provides real time, detailed analyses of chemical processes. The technique uses infra-red spectroscopy to
monitor supersaturation – the levels of chemical saturation in a liquid – required for crystallisation to begin to occur (see ‘Monitoring supersaturation’, over).
Most drug compounds are crystalline,
manufactured in batch process systems. Small changes in crystallisation process conditions, such as temperature and cooling rates, can significantly affect the structure of the resulting crystals, something that affects both their physical properties and their performance. “For example, when you
cool water the molecules in the water have to get into the right position to begin crystallising into ice crystals and the temperature can have a bearing on the size of ice crystals that are formed,” says Tariq Mahmud from the University’s School of Process, Environmental and Materials Engineering. “It’s similar with chemicals, although there’s a wider range of parameters to take into account.” The new technique uses
a probe attached to an infra-red spectrometer to measure the concentration of a specific chemical in solution. In laboratory experiments, this technique was used on the batch cooling crystallisation of chemical L-Glutamic acid (LGA). The information gained from the infra-red
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spectrometer is coupled with detailed statistical – or chemometric – data to provide a more detailed analysis of the crystallisation process than has been possible with other infra-red spectrometry techniques. Mahmud explains: “Using a chemometric
approach enables us to take many more parameters into account, which makes it a more reliable predictor of the optimum concentration levels required to produce a particular crystal structure.” The work draws on previous research and
experimental systems developed through the Chemicals Behaving Badly II initiative. Led by professor Kevin J Roberts at the University of Leeds, Chemicals Behaving Badly is an Engineering and Physical Sciences Research Council (EPSRC) and industrial consortium
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