ToF-SIMS depth profiling of oral drug delivery films for 3D visualization of active pharmaceutical particles

The size, shape, and spatial distribution of active pharmaceutical ingredient (API) are important physical characteristics of drug delivery systems that can affect the performance, stability, appearance, and even bulk properties of the end product. This study explores the feasibility of using time-of-flight secondary ion mass spectrometry (ToF-SIMS) for the 3D characterization of API particles in two commercially available oral dissolvable drug delivery films. It was found that ToF-SIMS imaging with argon gas cluster ion beam (GCIB) sputtering allowed production of 3D chemical maps that could be utilized to obtain size distributions of buprenorphine particles whose effective diameters ranged from approximately 6 mu m to 41 mu m, with shapes that were generally spherical with a few nonspherical structures. The particles were heterogeneously distributed both laterally and as a function of depth in the film. In addition, ToF-SIMS was able to differentiate between different oral drug delivery films based on differences in the spatial distribution of buprenorphine; in one case, the particles were distributed throughout the depth of the film, whereas the particles in the other case were localized close to the surface. Preliminary studies suggest that ToF-SIMS with argon GCIB sputtering may also allow us to provide a very rough estimate of the concentration of the APIs (factors of 2 to 4), namely buprenorphine and naloxone, at pharmacologically relevant concentrations inside organic drug delivery systems with a thickness of hundreds of micrometers.