A novel technique to quantify film--tablet interfacial thickness

The purpose of the project was to develop an x-ray photoelectron spectroscopic technique to quantify film-tablet interfacial thickness. Tablets containing 99% dibasic calcium phosphate were coated with an acrylic polymer containing chlorine (Eudragit RL 30 D). The film-tablet interface was defined as the region where phosphorous from the tablet and chlorine from the film coating were detected simultaneously. Five-minute intermittent ion-sputtering was used in conjunction with the conventional x-ray photoelectron spectroscopy to achieve depth profiling of the sample. The slow ion-sputtering rate of approximately 56 nm/min was overcome through sample preparation and analysis from the tablet side of the sample. This process eliminated the need to sputter through the entire film coating to reach the area of interest. Initially, only phosphorous from the tablet was detected. As the depth profiling proceeded, the chlorine signal increased and the relative intensity of the phosphorous decreased. By plotting the relative intensities of each element against the ion-sputtering time and using linear regression, the point at which the two lines intersected (tmid) was determined. By doubling tmid and multiplying by the estimated ion-sputtering rate, the thickness of the film-tablet interface was estimated to be approximately 34 microns. Further studies are needed to correlate the film-tablet interfacial thickness with the adhesive properties of coated solids.