QUANTITATIVE-ANALYSIS OF DRUG CONTENT IN SEMISOLID FORMULATIONS USINGSTEP-SCAN FT-IR PHOTOACOUSTIC-SPECTROSCOPY

Step-scan FT-IR photoacoustic spectroscopy in conjunction with a phase modulation technique (modulation frequency of 25 Hz) and digital sign al processing was applied in order to quantify the content of brivudin and dithranol in vaseline/drug ointment. The PA spectra of the mixtur es exhibit an excellent signal to noise ratio and bands belonging to t he drugs are clearly observable down to an 0.5 wt% concentration of th e drug. The integrated intensity of the drug bands with reference to a vaseline band was used as a measure of drug content. For comparison, the concentration of drug was determined by capillary zone electrophor esis for brivudin and by HPLC for dithranol. It appears that Beer's la w is fulfilled for the PAS data. No sample preparation was required fo r the PAS experiments.