THE SEPARATION OF INORGANIC IONS BY PAPER PARTITION CHROMATOGRAPHY W. JOE FRIERSON and MARY 10 AMMONS Agnes Scott College, Decatur, Georgia .
Tswett's introduction of chromatography as an analytical tool in 1906many variations of the method have been developed to meet individual needs. I n 1941 A. J. P. Martin introduced partition chromatography, ~rimarilyfor amino acid separations. This method is based on the principle of differential partition of a substance between two liquid phases, one of which is stationary and the other mobile, as compared with a partition between a solid and a liquid phase in the usual chromatographic methods. The mobile liquid is immiscible with water and is the solvent for the sample to be analyzed. This solution is poured through a column containing water which is held in place by some substance, such as silica gel. A few years later this same principle was applied to the use of filter paper. Strips of filter paper are suspended from a trough containing water and a partially miscible organic solvent such as n-butanol or phenol. A drop of the solution t o be analyzed is placed near the top of the strip and the paper and trough placed in a closed container for a certain period of time. The strip is then removed and developed with one or more re* gents to show the positions of the various substances. This method has been applied with success to the separation of certain organic compounds. An attempt was being made in this laboratory to work out a satisfactory procedure for the separation and detection of the common cations by means of adsorption columns. During this work it was thought that such a scheme for analysis would he much more rapid if the paper partition method would work with inorganic ions as well as with organic substances. Strips of No. 1Whatman filter paper 1to 4 cm. wide and about 35 em. long were hooked over the edge of a dish supported a t the top of a large crock. The dish contained the solvent, such as n-butan01 with a small amount of acetic acid. A few drops of the solution to he analyzed were placed near the top of the strip, just below where it hangs over the dish. The crock was kept closed until the solvent had moved down the strip nearly to the end, the time required depending upon the conditions but usually between 15 and 24 hours. The paper was then removed, allowed to dm, then developed. Except for a few preliminamruns with a few of the cations of Group 111 the work has dealt with the Groups I and I1 cations and H2S has been used for the developer. I n order to give some idea of the results obtained several of the strips are shown in the figure. Although a photograph of the strips shows only the dark bands SINCE
Ch.0matogr.m.
the others are very distinct on the strip and their positions indicated. In most cases the colors developed fade in a short time unless covered with a clear varnish. The actual colors of the bands are the characteristic colors of the sulfides. In the second, third, and fourth strips the mercuric ion moved with the solvent front. and gave a dark band further down. The results are quite reproducible, as may he seen by comparing the second and third strips. Hydrochloric acid, instead of acetic acid, was used with the fourth strip and it will be noted that the order of migration is different and that Bi and Cd moved further down the paper. The last strip shows the relative positions of Ni, Co, Fe, and Al. The acid used and the pH of the solution are important factors in determining the rate and order of the 37
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migration of the ions. If the hutanol is saturated with 1 N hydrochloric acid, pH about 1, the relative positions of some of the bands will be changed and migrrttion down the paper is more rapid. However this acid would not be satisfactory to use with the Ag, Pb, and Hg (ous) ions because on contact with the chloride ions their chlorides would be precipitated and no migration takes place. Although the use of different organic solvents and acids has not been investigated the butanolacetic acid solution, pH about 4, has given very satisfactory results. From the results obtained it would seem possible
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that a complete scheme for the separation and identification of inorganic ions may be worked out. Such a method would have several advantages. There would be a great saving in time. The actual working t,ime required for the separation and identification of a mixture containing the ions of Groups I and I1 was about thirty minutes. The materials used are very simple and inexpensive, and very small samples are used. Work is in progress on the separation of the ions of the other groups. The procedure as developed for the first two groups will be tested with a class in qualitative analysis during the fall quarter.
