Why is filter paper fluorescent? Typical filter paper used in chemistry lab (e.g. Whatman #1) exhibits autofluorescence in near UV with excitation maximum at 365 nm and emission maximum at 440 nm. It was reported in literature1 that fluorophores from filter paper can be extracted by PBS buffer in wide range of pH, and thus they are at least partially soluble in water. However, cellulose, the major component of filter paper, is not fluorescent in this wavelengths range and is insoluble.

What is the source of filter paper fluorescence? I assume it comes from paper pretreatment and bleaching, but what is chemical identity of fluorescent compounds in it? 


Danielson, T. L. et al.; Impact of filter paper on fluorescence measurements of buffered saline filtrates. Talanta 2003, 59, 601–604.
In the production of white paper, the bleached pulp is often treated with optical brightening additives (OBA), that absorb in the uv and emit in the blue range. If I remember correctly, a typical example is 4,4'-diaminostilbene-2,2'-disulfonic acid.



Here's an article from The Open Textile journal (OA) in which the compound mentioned above is used as a starting material in the synthesis of another optical brightener for textiles.