Traditionally, gravimetric analysis of aerosol samples has required pre-weighing the filter before sampling then weighing the same filter after the sample has been collected. The preparation step has now been eliminated with the use of Mathc-Weigh™ filters. PVC filters have been used for gravimetric analysis because of their inherent hydrophobicity. Now with the incorporation of a Pure Homopolymer of PVC (PH-PVC) in Omega's cassettes, the ultimate in efficiency, accuracy and versatility in gravimetric analysis, has been achieved.

Certain contaminants must be analyzed both gravimetrically and then identified by atomic absorption. In these cases the filter must be "digested", and Mixed Esters of Cellulose filters are more easily digested than PVC. For this application Omega has introduced the MCE version of matched weight filters in cassettes, with match of .050mg, increasing accuracy two-fold from existing MCE matched weight filters on the market now.

Each Omega cassette is pre-assembled with two membrane filters that are supported by a cellulose pad. The filters are matched in weight to within .025mg in the case of PH-PVC and .050mg in the case of MCE. The cassette is pneumatically closed with a controlled pressure to assure proper seal. The top filter collects the contaminant during sampling and the bottom filter acts as a "control". No pre-weighing or conditioning required by the user. Instead, each filter is weighed individually after sampling is completed. The difference in weight between the two filters corresponds to the weight of the contaminant collected within plus or minus .025 or .050mg depending on the filter type employed.