The growth rate of ibuprofen crystals in ethanol at 25 (± 0.1)°C was measured in two laboratories by two methods. In one, in-situ Process Analytical Techniques (PAT) a Mettler Toledo Focused Beam Reflectance Measurement (FBRM) particle analyser and a Fourier Transform Infrared Spectroscopy (FTIR) unit for concentration measurement were used. In the second, a conventional Malvern laser light scattering sizer and a refractometer for concentration measurement were used. Results from both techniques indicate that the growth kinetics were first order, i.e. n = 1 for growth rate G = kGsn. For n = 1, the PAT based method gives kG’= 27 (± 8%) µm/min/unit of I/E with size taken as a root mean square average chord length. The conventional techniques gave kG= 13 (± 15%) µm/min/unit of I/E with size now the volume equivalent size. The errors shown are the 95% uncertainty. The reason for the different kG values are attributed to differences in the measurement system. FBRM data indicates that the root mean square average chord length / median volume equivalent size ~ 2.0 (± 17%) for ibuprofen crystals, with this ratio generally considered an indicator for aspect ratio.
Keywords: Crystallization, Ibuprofen, Kinetics, PAT.