Quantitative Whatman filters are designed for gravimetric analysis and the preparation of samples for instrumental analysis. They are available in three sizes to meet your specific needs: Ashless: 0.007% ash maximum for type 40 to 44, and 0.01% for the 589-types - very pure filters suitable for a wide range of critical analytical filtration procedures Hardened low ash content: not more than 0.015% ash - treated with a strong acid to remove trace metals and to produce a high wet strength and chemical resistance. These filters are, in particular, suitable for Buchner filtration, wherein the strong smooth surface of the filter enables easy recovery of the precipitation Hardened ashless: 0.006% ash maximum - acid hardened for high wet strength and chemical resistance with extremely low ash content. The strong surface makes these filters suitable for a wide range of critical filtration procedures Type Hardened low ash The maximum ash content of these types is an average of between ashless and qualitatively. They are particularly suitable for Büchner-filtrations where it is desired that the precipitate after filtration is recovered from the filter surface. Other features include a high wet strength and chemical resistance comparable with acid in hardened, ashless filter paper. Type hardened ashless Quantitative filter paper with a high wet strength and chemical resistance. These papers are hardened in acid, so that an extremely low ash content is achieved. The robust surface makes them suitable for a wide range of critical analytical filtration operations. Each type offers a convenient combination of filtration rate, and particle retention.