No. 2991: WRITING IN COLORS

by Richard Willson

Click here for audio of Episode 2991

Today, we write in colors. The University of Houston’s college of engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Green leaves turn red and orange in the fall. Those colors were already there, hidden by the green of chlorophyll, which fades in the fall. Molecules called anthocyanins give red-purple colors to leaves, strawberries, and red apples. Orange-yellow carotenoids color carrots, bananas, and canaries.

We know all this largely from the work of Mikhail Tswett, who figured out how to separate the colored pigments from each other.

Mikhail Tsvet
Mikhail Tsvet. Photo Credit: Wikimedia Commons

Tswett was born in Italy in 1872 to a Russian father and an Italian mother. His mother died when he was a baby, and his father left him to be educated in Switzerland. Mikhail Tswett became a Professor of Botany in Warsaw, which was then controlled by the Russian Czar. He was very cosmopolitan; he published his work in French, Russian and German.

The work that made him famous came from studying photosynthesis. Tswett made extracts of leaves, and added chalk powder to neutralize natural acids that degraded the pigments. He found that most pigments stuck to the chalk. So he poured his extracts through a tube packed with a column of powdered chalk. The various pigments stuck to the chalk, and formed separate differently colored bands in the tube. Tswett could isolate pure compounds by cutting the bands out of the chalk column — now we know he could have washed them out one at a time by flowing stronger solvents through the column.

As he put it: “Like light rays in a spectrum, so the different components of a mixture of pigments are dispersed in the chalk following a set pattern, and [they] can be determined from there. I call such a preparation a "chromatogram"” (which means “color-writing”). Some think Tswett chose this name because his name means both “color” and “flower” in Russian.

Chromatography Tank
A Diagram of a Chromatography Case. Photo Credit: Wikimedia Commons/Theresa Knott

Tswett’s new method went largely unnoticed for 30 years. He originally published it in Russian, so his work wasn’t read by a very wide audience. The great chemist Willstatter couldn’t reproduce Tswett’s results, and disputed his claims. And Europe was in chaos in the early 1900s.

Though, sadly, Tswett did not live to see it, chromatography eventually became very popular. He had predicted it could be used on other substances, and had tested over 100 adsorbents for packing into columns. There are now thousands of adsorbents, used in many new forms of chromatography, and we run things out the end of the column into detectors and collectors.

Chromatography of gases is a standard tool for analyzing water and petroleum as vapors. A special form of chromatography even serves as the basis of the home pregnancy test.

And chromatography is now used to make things, not just analyze them. Giant columns separate tons of sugars which are collected as they emerge from the column. And most modern pharmaceuticals, including insulin and cancer drugs, are purified by chromatography.

All this, from looking at the colors of the fall leaves.

I’m Richard Willson at the University of Houston, where we’re interested in the way inventive minds work.

(Theme music)

A popular article on Tswett from Chemistry World http://www.rsc.org/chemistryworld/2014/01/mikhail-tsvett-column-chromatography-separation

Encyclopedia.com entry on Tswett http://www.encyclopedia.com/doc/1G2-2830904382.html

An article on the 100th anniversary of Tswett’s presentation of chromatography in Warsaw http://www.sciencedirect.com/science/article/pii/S1570023203008183

Translations of Tswett’s original work https://web.lemoyne.edu/giunta/tswett.html

Instructions for doing paper chromatography at home http://www.scienceprojectlab.com/paper-chromatography-experiment.html

One of many good online videos describing a home demonstration of paper chromatography https://www.youtube.com/watch?v=_S17nMwZwe4

This episode first aired on February 13 , 2015.