Re-examination of "Litmus" from an Educational Point of view (I) 　―A Simple Method to Separate of the Main Constituent of Litmus and Measurement of the pH-range of Impure Azolitmin―

Abstract

A liquid chromatographic technique, used potato starch, can be applied to separate of the several constituent of litmus dye. The simple apparatus of it is shown in figure 1. The tube of column of it is made from glass or polyethylene because it must be transparent or semitransparent. A developing solvent is water or 30% ethyl alcohol. A suitable of potato starch is kneaded by the solvent, and it is poured into the tube. The starch presently precipitate and the column is made. When the almost solvent soakes into the column, a litmus solution is added to the top of column. In this time, this solution must be filtered and concentrated, and the volume of litmus solution must be less than about 5 mm in depth. Next, in the moment of the litmus solution almost soakes into the column, the developing solvent is sufficiently added again. Soon, the litmus is separated several constituent in column. At first, a russet dye effuses after about one hour. This effuluent is a impure Azolitmin which includes a little pink dye. Litmus is a mixture, so its pH-range of color change is uncertainly. But the pH-range of this impure Azolitmin has an approximately constant range which is laid between from pH 5. 0 (red) in the case of using weak acid (for ex. CH3COOH) to pH 8. 0 (blue) in using of weak base (NH4OH). Besides, this impure Azolitmin has also two ranges, one is pH 3.0 (orange)-4.0 (red) in using of strong acid (HCl) and another one is pH 9.0 (red)-11 (blue) in strong base (NaOH).