Guido Heinsohn

Observation of a Penetration Depth Gradient in Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Imaging Applications

Fourier transform infrared (FT-IR) spectroscopic imaging offers the possibility of combining spectral and spatial information, thereby enabling a spatial chemical visualization of samples. Thus, sample areas can be analyzed by infrared spectroscopy with high lateral resolution (up to 3–4 lm). The performance of FT-IR imaging equipment has been discussed by many authors, and numerous applications have been described. An important application area is the analysis of polymers, including diffusion and dissolution processes. Another field of research is the analysis of skin sections, biological tissues, and biomaterials. Pharmaceutical issues such as drug release or dissolution of tablets have also been analyzed by FT-IR imaging. Besides transmission measurements, attenuated total reflection (ATR) imaging is often applied. In this note we report on investigations of homogeneous samples by ATR imaging measurements with the FastIR accessory. In order to check the illumination uniformity of the ATR crystal, we chose a homogeneous liquid sample (paraffin oil) because of its perfect contact to the ATR crystal. However, despite this perfect contact, the integrated absorbance for a particular band is not constant for the imaged area. Instead, an absorbance gradient in the Z direction of the image (direction of the IR beam from the source to the detector) is revealed. These findings were also analyzed for two solid samples (adhesive tapes) and an emulsion. The influence of this absorbance gradient on ATR imaging results will be discussed.

Confocal Raman investigation of diffusion processes in monolithic type transdermal drug delivery systems

Abstract Release from a transdermal drug delivery system (TDDS) can either be controlled by diffusion in the adhesive, by diffusion processes in the stratum corneum of the skin or a combination of both. In this study, diffusion processes in monolithic type TDDS were investigated using confocal Raman microscopy. An acrylic adhesive (Duro-Tak 180-129a), a rubber adhesive (Duro-Tak H1540) and a silicone adhesive (BIO-PSA 7-4202) were used. Skin permeation of the model drug Paeonol from these adhesives was investigated. Release studies on porcine cadaver skin were carried out. Solubility of Paeonol in the different adhesives was measured. Diffusion coefficients of the drug in the TDDSs were calculated from confocal Raman depth scans, the diffusion coefficient in the stratum corneum was calculated using tape stripping. Solubility of Paeonol in the acrylic adhesive was the highest with 30 g/L among the tested systems. Paeonol had a solubility of 6 and 9 g/L in the silicone and rubber based system. Diffusion coefficient rank order was BIO-PSA 7-4204 > Duro-Tak 180-129a > Duro-Tak H1540. Release on porcine cadaver skin from the silicone was the highest followed by the rubber and the acrylic adhesive. During release studies on porcine skin with Duro-Tak H1540 no concentration gradient of Paeonol could be monitored in the Raman depth profiles, whereas in the stratum corneum an apparent diffusion gradient was detectable. Solubility of a drug in the adhesive dominated the release properties, high-diffusion coefficients of drugs in adhesives do not necessarily lead to high release rates from adhesives.