Surface Area Testing

The surface area is an important parameter for solid material, which provides information on the available void spaces on the surfaces of individual particles or aggregates of particles. The specific surface area associated with particle size, particle shape, and oftentimes particle porosity. The surface area of a solid pharmaceutical plays a role in the drug development and manufacturing, can affect some properties like dissolution and bioavailability. For example, clay (such as aluminum silicate), used as stomach medicines, is porous materials and has a large surface area, which is benefit for absorbing gastro-intestinal toxic bacteria and abnormal matter, absorbing surplus moisture to stop diarrhea, and protecting the gastro-intestinal membrane. However, in some case, as surface area increases, the material will go into solution more quickly and be available for absorption at a rate, which could result in negative pharmacodynamic implications, eventually leading to product failure due to safety concerns. Thus, surface area is a critical part of solid pharmaceutical materials characterization, it can be used to predict bioavailability, and further it is useful in evaluation of product performance.

Surface area measurement is usually done by gas adsorption method. Among the gas adsorption methods, the most widely used is the Brunauer, Emmett, and Teller (BET) that are well-known. Alfa Chemistry possess the latest high-performance Fully Automatic Surface-Area Instruments. Supported by experienced experts, our surface area testing capabilities highly exceed other companies in this field, we can assure customers the highest quality data.

Gas Adsorption Method

The physical adsorption of a gas on a solid can be achieved since there a relatively weak forces (Van der Waals forces) between the adsorbate gas molecules and the adsorbent surface area of the test powder. The amount of gas adsorbed can be measured by a volumetric or continuous flow procedure. By physical adsorption of a gas on the surface of the solid and by calculating the amount of adsorbate gas corresponding to a monomolecular layer on the surface, the surface area of a powder is determined. The analysis data obtained through gas adsorption method provides information regarding the physical characteristics of the solid, excepting specific surface area, as well as including porosity, total pore volume, and pore size distribution. Gas adsorption method can also provide valuable information on the physical structure and shape of the pores. Gas adsorption method is often used to test surface area and porosity measurements in the pharmaceutical industry. Moreover, the surface roughness of a pharmaceutical product can also be measured by gas adsorption analysis, which influences the performance characteristics of pharmaceutical products such as oral tablets, and dry powders for inhalation.

The Brunauer, Emmett and Teller (BET) method is the most popular method applied for the surface area measurement of pharmaceutical powders. BET method provides precise specific surface area evaluation of materials by using nitrogen as gaseous adsorbate. The testing of surface area by BET method is a relatively simple measurement to carry out. It is available for a range of disperse, solid microporous to mesoporous materials.

Alfa Chemistry is an expert in surface area measurement. Please contact us to ask for help and support.