Sister Eleanor Marie, S.S.J. Chestnut Hill College Philadelphia, Pennsylvania
Column Chromatographic Analysis of the Metal Ions
T h e author agrees with those who argue that qualitative procedures are of proved pedagogical value when used wisely. We have developed and made completely workable a method of column chromatographic analysis which is simpler, quicker, and as accurate as conventional methods. The theory, the group separations, and the ion identifications of the classical method have been retained. The analysis scheme is that first presented by Fillinger.' Our modifications have been based on extensive student experience. We have determined the sensitivity of all the tests, studied the effect of the acidity of the solution on the aluminum oxide column, and developed a few innovations in techniques such as using Na2S04 as the precipitating reagent for Pb++ to eliminate obnoxious fumes. The relative amounts of the ions present can be observed in the chromatographic method since in many cases the hand width is significant. The student can recognize quite early in his work whether the ion is present in trace amounts or in amounts greater than 1%. This is especially true if he is taught to calibrate his 2-ml bulb pipet and to use a fixed amount of his
' FILLINGER, H. H., THIS JOURNAL, 29,286 (1952).
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Journal of Chemical Education
solution. The tests are extremely sensitive. For example, 0.0125 mg/ml of the silver ion gives a definite rust band 1.5mm wide with KzCrtOa. Even with lead present, the band width for silver is 0.25 mm and the lead band is 0.75 mm; these are easily recognizable. We have found that the acidity of the solutions has a significant effect on the type of band produced. Careful control of the pH of all solutions is necessary. We advocate the use of column chromatography for the following reasons: The apparatus is simple and inexpensive. A student can make easily the twelve or fifteen 6-mm glass tubing columns he needs. The method speeds up laboratory work. An entire analysis can he completed with a good degree of accuracy in a single laboratory period. Only a few drops of solution are needed for each analysis; hence the student has sufficient filtrate to make several runs if necessary. The student gains experience with chromatography while learning qualitative analysis. The author is indebted to the Petroleum Research Fund for a research grant (494B) which supported this study, to her honor students for the laboratory work on the scheme, and to Sister Patrick Marie for many helpful suggestions. Copies of the experiments and directions for preparing reagents may be obtained from the author for $3.
