When conducting gravimetric analysis, it is important to precisely measure the change in mass of your collection membrane to accurately assess the load of collected particles. Filters are weighed before and after filtration. The initial weight is subtracted from the final weight and a Total Suspended Solids (TSS) number is calculated.
To simplify your analysis, Merck offers matched-weight membrane pairs to eliminate the pre-weighing step. Matched-weight filters matched in pairs to within +/- 0.1 mg for gravimetric analysis.