An in-line filter holder holds either a 25 mm or 47 mm filter, depending on the model, in a fixed sample line. Filters are the primary standard used for determining aerosol concentration. Filters collect particulates by interception, inertial impaction, and diffusion as the aerosol is drawn through them. The sample flow rate is a calibrated flow. Filters are weighed before and after sample collection. The weight differential is determined: post sample weight – pre-sample weight. The volume of air sampled is calculated: sample flow rate x sample time. The quotient of differential weight and sample volume is the mass per unit volume aerosol concentration. Sample weight differential can also be determined by chemical analysis rather than gravimetrically.
A passive air filter is usually a type of HEPA (High Efficiency Particulate Absorption) filter that is positioned in the aerosol delivery line of an inhalation exposure system. It is used on negative pressure system to allow passive or negative pressure flow to enter the system. The filtered air acts to dilute and dry the aerosol. A passive air filter also acts as a pressure buffer and enables steady maintenance of chamber pressure and easy, rapid adjustments. In positive pressure systems it acts to scrub particulates out of the air stream before it exits the system.
Solubility filters are used to determine the solubility of different compounds. This is useful for the drug discovery and chemical industry researchers. They are used to determine solubility of test articles and vehicles. Basically, the test article is put into a solution and passed through the filter. Whatever is left behind on the filter is the insoluble fraction.
More information coming soon.