John T. Stock ond A.
V. DeThomas
University of Connecticut
Storrs, 06268
Microapparatus for Demonstrating Electrophoresis on Paper
A
safe and simple demonstration of electrophoresis in liquid systems can be energized by a 9-v pocket radio battery.' The same power source can be used to show electrophoresis on a moist filter paper strip. The electrodes, which span the entire width of the strip, are mounted about 10 mm apart, so that the voltage gradient is comparable to that encountered in paper electrophoresis on the conventional scale.2 Two small rectangles of '/s-in. thick transparent Lucite form the top and bottom plates of the apparatus. Parallel grooves (see the figure), filed 10 mm apart on the upper side of bottom plate A, locate the 28-gauge platinum wire electrodes, BB, so that about half of the cross section of the wire projects above the Lucite surfacae. The wires pass through tiny corks, CCCC, which are cemented to the edges of A. Top plate D is about 1 mm narrower than A and has a paper gasket E about 1.5 mm wide cemented to its underside. The gasket has narrow slots to allow entry of the other half cross section of the electrode wires. Electrophoresis is carried out on a Whatman No. 1 filter paper strip F of approximate dimensions 20 X 3 rnm. A light pencil line is drawn across the width of the strip at its center. When the paper is in place, the pencil line should he parallel to the electrodes and midway between them. The apparatus is held together by two small bulldog clips GG, as shown in cross-section a t (a). For clarity, the parts are shown slightly separated. The battery leads carry appropriately marked miniature alligator clips that can be attached to the projecting ends of the respective electrode wires. The following steps are carried out rapidly when a run is to be made. After being dipped into a suitable background solution, the strip is gently pressed between two sheets of filter paper. Using a glass hair or, when permissible, a fine steel pen point, a narrow band of the solution to be tested is streaked along the pencil line. The strip is then properly located on the electrodes, the top plate and clips are put in place, and the battery is connected. Movement of a colored substance
can usually be detected after 5-10 min and is normally very obvious after about 20 min. Because of the shortness of the electrophoresis path, the separation of a mixture of substances is not usually successful. One per cent solutioi~sof malachite green (in water) and of bromphenol blue (in ethanol) are useful for demonstrating movement. to the cathode and anode respectively. Some red, yellow, blue, and green food dyes3 obtained from a supermarket undergo rapid electrophoresis to the anode. A suitable background solution is 0.04 M ammonium acetate in either 0.1 M acetic acid or 0.1 M ammonia. Distied water alone is sometimes effective. With a background solution of 0.1 M perchloric acid, the existence of both cationio and anionic complexes of iron(II1) and thiocyanate ion can be sugge~ted.~A red streak of liquid that is 0.1 M in iron(II1) nitrate and 0.06 31 in potassium thiocyanate moves towards the cathode. If the thiocyanate concentration is raised to 1 ill, the movement is toward the anode. Strips cut from pH-sensitive test papers can be used
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This apparabus wai developed with the part,ial support of the National Science Foundat,ion'sprogram for the design of science teaching equipment. A. V., J. CHEM.EDUC.,43, 'STOCK,J. T., AND DETHOMAS, 436 (1966). J. G., "Paper and Thin Layer 2 S ~I., ~AND~ FEINBERG, ~ , Chromatography and Electrophoresis" (2nd Ed.), Shmdon Scientific Co., La.,London, 1965, p. 121; and GROSS,D., Analyst, 90, 380 (1965). a Baker Extract Co., Springfield, Mars. JOSEFOWICZ, E., AND MASWWSKA, J., Theory S t r u t . Complex Compds., Papers Symp., Wroclaw, Poland, 1962, 525 (Pub. 1964); C.A. 63, 17456f (1965).
Apparatus for the demonstrotion of elertmphoreris on paper, see text for explanation d parts.
Volume 44, Number 7, July 1967
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to illustrate the movement of hydrogen and hydroxyl ions in an electric field. Distilled water is the only liquid applied to such papers. Blue litmus paper develops a red zone that moves rapidly toward the cathode. The blue zone produced on red litmus paper moves more slowly toward the mode. The effect on
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universal pH paper is more dramatic, since both blue and red zones form and then move in opposite directions. Since the current per strip is only a milliampere or so, a single small battery can power several of these microelectrophoresis experiments that are running at the same time.
