Fluorescence of amino-acids, peptides and amines on filter paper.

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THE fluorescence of amino-acids and peptides on dry filter paper1 is of great value for locating these substances after paper chromatography, and has been found useful in quantitative work2 since it avoids destructive treatment with reagents such as ninhydrin. It also enables substances to be eluted for further investigations from sheets of chromatograms where gross irregularity of solvent flow renders the use of marker strips3 inaccurate as guides for cutting. Unfortunately, marked variations in fluorescence are often observed when identical chromatograms are run on sheets of No. 4 Whatman paper from different packets of papers or even on adjacent sheets from the same packet4, and batches of papers are occasionally encountered on which no fluorescence at all can be observed at normal nitrogen-levels. As Phillips1, quoting De Ment5, considered fluorescence of amino-acids on paper to be due to excitation of the acids themselves by ultra-violet light, it seemed possible that some impurity present in ‘bad’ fluorescent papers might therefore be quenching fluorescence. Sheets from a particularly bad batch of No. 4 Whatman paper could not be improved, however, by washing with water, dilute sodium hydroxide, hydrochloric acid or with solutions of 8-hydroxyquinoline or dithizone.