COMPARISON OF WRITING INKS BY PAPER CHROMATOGRAPHY.

This article deals with the comparison of writing inks by paper chromatography. The chromatographic method of analysis is especially applicable to dye-base inks. Comparisons are further facilitated by the frequent occurrence of several dyes in a single ink. Two inks in a liquid form can be readily compared by chromatography using only distilled water and filter paper. This may be accomplished as follows: A droplet of a known sample A and a droplet of an unknown sample B are diluted with distilled water in a ratio of 1 to 20, using separate crystallizing dishes. One end of a strip of Whatman #1 filter paper about 10 cm long and 6 mm wide is dipped in each of the dilutions. After the dilutions rise approximately one-fourth the length of the paper, the strips are withdrawn. If comparisons of the two chromatograms reveal bands of different color and elementary ingredients, the two inks are obviously dissimilar in composition. To establish the identity or diversity of two inks in dried form, simply place a minute droplet of water in a pipette or a platinum wire micro-loop of .4 mg. capacity, directly on a written stroke of each document, preferably where there is a generous deposit of ink. As soon as dissolution takes place, generally within two minutes, take up this residue with a narrow strip of Whatman #1 filter paper about 1 mm wide and 6 mm long, holding it obliquely on the area being treated for the time necessary to absorb the entire droplet. Then proceed with the second phase of the treatment mentioned under liquid inks, except that the time allowed must be restricted, due to the use of the smaller strips. Where the chromatograms of the two inks match, their identity can be further established by preparing a third chromatogram.