Simultaneously measuring concentrations of a model drug and a model excipient in solution using ultrasonic spectrometry

A newly commercialized high-resolution ultrasonic spectrometer was evaluated for simultaneously measuring concentrations of a model excipient (hypromellose acetate succinate polymer, HPMCAS, CAS No. 71138-97-1) and a model drug (Fenofibrate, CAS No. 49562-28-9) in acetone solution. It was demonstrated that the measurements of both velocity and attenuation had sufficient accuracy and precision. The velocity was found to be directly proportional to concentrations of both HPMCAS polymer and Fenofibrate in solution. The attenuation was found to be directly proportional to concentration of HPMCAS polymer in solution. By establishing linear relationships of measured velocity and attenuation to the concentrations of HPMCAS polymer and the Fenofibrate in a series of standard solutions, it was feasible to simultaneously analyze concentrations of both HPMCAS polymer and Fenofibrate in a test solution. However, it was found that both temperature and moisture had significant influence on the measurement. While the change in velocity was inversely proportional to the change in temperature, the change in velocity was directly proportional to the change in moisture content in solutions.