I'm wondering what, other than cellulose, might be contained in filter paper (the kind routinely used in Buchner filters / normal funnels).

A search here on Chemistry Stackexchange shows that at least one additive is used to modify the visual appearance of some filter paper (for improved "whiteness" / "fluorescence").

What additives may be contained in filter paper? What are their properties (solubility and potential chemical interference)? And how could one get rid of them prior to use, without consequence on the paper's filtering properties?

When used to filter away precipitated contaminants I usually rinse my filters in hot purified water before use (more with residual acid traces in mind). How would you guys prepare them for extreme minimal contamination?

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    $\begingroup$ Depends on which ones you buy. What are you concerned about? mn-net.com/filtration/cellulose-filters-information $\endgroup$
    – Waylander
    Jun 28 '20 at 8:30
  • $\begingroup$ The manufacturer in the link seems like a consciencious one at reasonable pricing. I am concerned about possibly (a) unknowingly (b) contaminating my products (c) with a set of substances whose nature I ignore. I must write that given the intended use cases I wouldn't have expected manufacturers to add anything to paper filters other than to improve their filtration characteristics (e.g. mechanical resistance when wet), and I would have expected them to disclose any additives on the package. $\endgroup$
    – Hans
    Jun 28 '20 at 10:14
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    $\begingroup$ Have you considered glass fibre or a dual piece setup, usually for mobile phases using Teflon coating which has minimal if any, leaching $\endgroup$
    – Beerhunter
    Jun 28 '20 at 10:20
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    $\begingroup$ If the filter paper has been bleached, with say a hypochlorite (OCl-), possibly a small amount of chloride, and if using NaOCl, test for sodium as well. Now, if bleached with say H2O2, check for residual amounts of commonly employed stabilizers (like H3PO4) to lower the pH of the H2O2 and increase shelf-life. If ClO2 used, again chloride. $\endgroup$
    – AJKOER
    Jun 28 '20 at 21:16
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    $\begingroup$ If additives would leech from the filter paper, washing the paper before filtration (and collecting the wash separately for potential analysis) should remove any contaminants. I routinely do that with cotton woll, when I use that as a filter: prepare filter, wash with a couple of ml of solvent, discard, filtrate my mixture. $\endgroup$
    – Jan
    Jun 29 '20 at 7:57

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