William Cherbro
Illinois Institute of Technology and The American Meat Institute Foundation Chicago, Illinois The
A Simple Rapid Method for Loading Paper Chromatograms
The usual method of loading paper chromatograms involves applying 1 to 5 p1 of sample onto the origin with some type of capillary micropipet. I n addition, some special drying apparatus is usually employed to restrict the size of the spot and shorten the interval between applications. Even so, it is quite laborious to load more than a few p1 onto a chromatogram and difficult t o produce small, uniform spots. These requirements and difficulties can be reduced by the use of small paper discs, saturated with the sample to be analyzed, dried, and a f h e d to the origin of the chromatogram. Discs 6 mm in diameter can be made from chromatography paper with an ordinary paper punch. Such discs have a very uniform saturation capacity and take up approximately 3 p1 when touched t o the surface of a solution. A convenient procedure for using such a disc is to transfix it with a straight pin, touch it to the surface of a test solution, stick the pin into a cork, and allow the disc to dry. The disc may then he affixed to the chromatogram by making two short, parallel slits about 2 mm apart a t the desired origin and slipping the disc between the strip thus formed and the main body of the chromatogram. The uniform saturation capacity of such discs permits quantitative comparisons between the results obtained from discs saturated in different solutions. Alternatively, larger volumes of solution can be loaded quite rapidly onto the disc by t h e following
procedure. The disc is transfixed with a straight pin so that it is a t the end opposite the point. The pin is then thrust into the underside of some surface or a cork so positioned that the pin is vertical but the disc carrying end is the lower. Any pipet calibrated in 0.01 ml units can then he used t o allow up to 50 pl to flow onto the disc. A pendulant droplet may form on the disc, hut dripping will not occur if no more than 50 pl is added. The disc can then be allowed t o air dry or a hot plate can he positioned a few inches below the disc t o hasten the drying. The dried disc is then attached t o the chromatogram in the manner described. This technique has given particularly satisfactory results when used in conjunction with circular chromatography. Two views of such an assembly are shown in the illustration, which also illustrates the general manner of disc attachment. The disc is affixed a few mm below the apex of a triangular wick. The wick apex is then inserted through a small slit (2-3 mm in length) in the center of the circular chromatogram, and the assembly is placed on the solvent-containing Petri dish in the manner illustrated. Superior resolution can he achieved with onlv a minimum of exnerience. Journal paper No. 145, American Meat Institute Foundation.
Volume 36, Number 2, February 1959
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