Quantitative filter papers are widely used for quantitative and gravimetric analysis in the lab. To make them ash-less and achieve high purity, a special production process with acid is required in production, washing with HF or HCl acids, cleaning with demineralized water followed. The specific processes make the quantitative filter papers achieve two characters: high resistance to wet state and low ash content.
Called as ash-free filter paper as well, the quantitative filter papers can be divided into three formats, ashless, hardened low ash and hardened ashless.
With 0.007% ash maximum for grades 40 to 44, ashless quantitative filter papers are ideals for a wide range of critical analytical filtration procedures.
Treated with a strong acid to remove trace metals and produce high wet strength and chemical resistance, hardened low ash quantitative filter papers have 0.015% ash maximum. These filters are particularly used for vacuum filtration, as the tough smooth surface of the filter can recover precipitates easily. Its high wet strength and chemical resistance are similar to the acid hardened ashless filter papers.
And hardened ashless quantitative filter papers, with 0.006% ash maximum, are hardened by acid. The process gives high wet strength and chemical resistance with extremely low ash content.
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