|Characterization of Mesoporous Silica Used for Drug Delivery by Sorptive Interaction - Multiple Headspace Extraction - Gas Chromatography
|Exploiting Separation Science
|Mr Juan Aspromonte
|Mr Kris Wolfs
Prof Ann Van Schepdael
Prof Erwin Adams
|Pharmaceutical Analysis - KU Leuven
Abstract Information :
As mesoporous silica (MPSi) is often used for drug delivery systems, suitability and homogeneity must be assessed continuously. The physicochemical characterization of these materials relies on the use of adsorption isotherms and some spectroscopy and microscopy. The use of those techniques are somehow limited, probably due to their important cost and low availability in most pharmaceutical laboratories. Given that manufacturers of silica only provide limited information about the properties of their products, a first screening of MPSi to reduce the number of drug delivery candidates for final testing would be useful. Moreover, a batch control technique for MPSi materials before being used in the production would be truly valuable.
MATERIALS AND METHODS
This work presents a simpler alternative to classify and qualify solids for their use in drug delivery by characterizing their sorption capacity. Using a multiple headspace extraction - gas chromatography (MHE-GC) experiment constituted by a mixture of solvent probes and a MPSi sample that allows to evaluate the sorption interaction (SI), different MPSi are classified by comparing the slope of the semi-logarithmic plot of the peak areas versus the extraction step (MHE plot).
In order to simplify the system, only a gas-solid interphase is considered. This is experimentally achieved by placing a small amount (20 mg) of the MPSi sample into a regular headspace vial and 8 µL of the liquid solvent probe mixture in a smaller vial that is placed inside the larger one. Then, the large vial is capped and thermostatted in the autosampler oven for a time long enough to guarantee full evaporation and reach an equilibrium between the solid and the gas phase. Finally, a 9 steps MHE-GC routine is carried out.
Four solvents (n-pentane, n-heptane, 1-butanol and 1-hexanol) were used as probes to evaluate the adsorption capacity of five MPSi samples. The slopes obtained in the MHE plots for each probe in the mixture can be compared with the slope obtained when the experiment is run without the MPSi sample by calculating their ratio. The difference of this ratio between the alkane and alcohol probe of the same chain length (methyl plus functional group number) is then used to evaluate the adsorptive capacity of the MPSi samples. A good linear fitting of the MHE plot was obtained in all cases (R² > 0.99) and the method proved to be reproducible (%RSD for the slope calculation < 1% in all cases). The classification of the MPSi is in line with the known characteristics obtained by other methods.
A simple comparison of the slopes of the MHE plot obtained in the SI-MHE-GC experiment allowed a classification of the MPSi samples in terms of their sorption capacity. The proposed method led to rational results on the investigated samples (characterized by other methods). Moreover, the instrumentation used is widely found in pharmaceutical laboratories and can be applied straightforward, making it an appealing choice for classification and qualification of new drug delivery materials.