Adalberl Wollrab Justus Liebig University 63 Giessen, Federal Republic of Germany
I
Chromatography on Chalk
m a y be regarded Chromatography o n a piece of as chromatography o n a n "open column." T h e separation of dyes o r colored natural substances on a piece of chalk is impressive a n d can he carried out a t any secondary schoolchalk is readily available there, t h e procedure is simple, a n d t h e separation of t h e mixture of substances is completed within a few minutes. This method has also been applied in a freshman course in which separation methods in organic chemistry were being dealt with.
Procedure T h e r e are two possihle modifications I) Similar to thin-layer chromatography the solution of the mixture, which is to be separated, is, by means of a capillary, apdied to a mot about 1 cm above the end of the chalk (see Fig. la). 2) A piece of chalk (which can be sharpened to a point) is dipped into a clockglass filled with the solution of the mixture to be separated. The solution should be allowed to rise up to -74 in. on the piece of chslk (see Fig. lb).
Figure 1. a. Application of solution to chalk. b. Dipping chalk imo solution. c, Lime drawn on chalk fol separating w'* fell-%pmarkers.
From here on the following instructions apply for b o t h procedures With a psir of tweezers the piece of chalk is put into a narrownecked 100-ml Erlenmeyer flask filled with 8 ml of pure solvent that is called developer. When working according to procedure (2), the chalk should be lowered into the developer very slowly and carefullv. so as not to wash out the colorine mixture which is to be separated. The Erlenmeyer flask is closedwith a cork (see Fig. 2). The developer should rise to X of the chalk-length to achieve a good separation. Separation on a Preparative Scale
For preparative experiments, t h e procedure mentioned in (2) should he chosen. After the development t h e chalk is c u t u p with a knife. T h e pieces with t h e zones of pure suhstance a r e crushed in a mortar a n d t h e substances a r e extracted from t h e chalk with a suitable solvent. T h e chalk is removed by filtering the solution a n d t h e solvent is distilled.
Specific Separations of Coloring Substances Water Soluble Felt-Tip Markers A continuous or dotted line is drawn directly onto the piece of chalk about 1cm above the end (see Fig. Ic). All four sides of the chalk can be used for the separation of a different mixture with the same developer. When using old or dried-out markers, one simply takes out the refill, cuts off a piece about 5 mrn long, puts it into a clockglass and adds either 0.5 ml water or ethanol, depending on the solubility of the dyes. Water or ethanol is used as developer according to the polarity of the mixture of substances to be separated. A good separation is demonstrated especially well with brown felt-tip markers. hks The ink is applied directly onto the chalk. The upper phase3 of butanal-llacetic aeidlwater mixture 4 1 5 is used as developer. Good separation was achieved, for example, with red ink Pelikan Brilliant Red 4001. 1 Sen,
B. N., Z. Anorg. Allg. Chern., 268.99 (1952). Schricker, H., Praxis der PhysiklChernie, 13, CH 10 (1954). Pfeil, E., Chemie in Unserer Zeit, 2,58 (1969).
Figure 2. Placement of chalk into developer.
Ball Point Pen Colors Take a regular refill and write on a piece of paper first to make sure it works; then paint an area of 1im2 in the middle of a small porcelain dish (gently-do not press too hard!). The color substance is dissolved in a few drops of chloroform (or ethanol). Aecording to brand name products chloroform, ethanol, or butanoll ethanollwaterlacetic acid (60:20:20:0.5) are used as developer. Azo-Compounds A 5% solution of the substance mixture in petrolether is applied to the chslk. The azo-compoundsare developed with petrolether. RP umlues Am-compounds 1O . 0.7 Ambenzene 4-Dimethylaminaazobenzene 0.1 0.05 Scarlet R (2 isomers) Plant Coloring Substances From Grass
Five grams of grass are cut up with a psir of scissors and ground in a mortar, together with 10 g fine sand and 5 ml of acetone. The ground grass is put onto a filter and 5 ml acetone and 10 ml petrolether (40-60% bp) are poured over it. The filtered liquid is gathered in a test tube, the upper phase is pipetted off, and the solvent is then distilled from it. The residue is dissolved in a few drops of petrolether and the tip of the chalk is dipped into this solution. In this ease benzene is used as developer. Volume 52, Number 12, December 1975 / 809
Substances carotines xanthonhvll rhlc~rodh~l b chlorophylt n
Color Zones yellow vellow vellowish rreen hluiih green
RF Values 1.0 0.1 0.3 0.2
Yellow Components in Flower Petals Two grams of flower petals are crushed in a mortar with 5 g of
810 / Journal of Chemical Education
fine sand and 5 ml of acetone. The procedure is the same as in the preceding experiment, the only difference heing that petrolether is used as developer. Acknowledgment I am indebted to Mr. Reiner Ruckelshausen for experimental help.
