Mikhail Tswett Biography

Although recognized only belatedly, Mikhail Tswett (sometimes spelled Tsvet) was the first to lay out in detail the methods of the separation technique called chromatography. Tswett himself regarded chromatography only as a tool in his chemical and biological studies; his purpose was to separate and identify the many different pigments in leaves and other plant parts, and he considered it merely an improvement on existing techniques such acid-extraction, base-extraction, and fractional crystallization. Since he first described this process, many kinds of chromatography have been developed, and no laboratory is considered complete without a number of chromatographic instruments.

Mikhail Semyonovich Tswett was born May 14, 1872, in Asti, in the northwest part of Italy about seventy miles from the Swiss border. His parents were Semyon Nikolaevich and Maria de Dorozza Tswett. His father was a Russian civil servant and his mother, who was very young, died soon after his birth. His father returned to Russia after her death, and left his son with a nurse in Lausanne. Tswett was educated in Lausanne and Geneva, becoming multilingual in the process. He received his secondary education at the Collège Gaillard in Lausanne and the Collège de St. Antoine in Geneva; he entered the University of Geneva in 1891, studying chemistry, botany, and physics. His baccalaureate in both physical and natural sciences was awarded in 1892. He began plant research during his undergraduate years, earning the Davy Prize while a doctoral student with a paper on plant physiology that was subsequently published. In 1896 he defended his thesis, "Études de physiologie cellulaire," and received his doctoral degree.

Thereafter he moved to Russia, and in 1897 he began working at the laboratory of plant anatomy and physiology at the Academy of Sciences and the St. Petersburg Biological Laboratory. His academic horizon was limited by the fact that foreign degrees were not recognized in tsarist Russia, and he set to work earning another master's degree in botany at Kazan University. He finished in 1901, with a thesis in Russian whose title is translated "The Physicochemical Structure of the Chlorophyll Grain." In 1902 Tswett became an assistant in the laboratory of plant anatomy and physiology at the University of Warsaw, which was under Russian control at that time, where he became a full professor in 1903. In 1907 he took on the additional task of teaching botany and microbiology at the Warsaw Veterinary Institute; a year later he was also teaching at the Warsaw Technical University. He resigned his teaching post at the University of Warsaw but took a second doctorate there in 1910 with a dissertation on plant and animal chromophils. This apparently led to his only book, published in the same year, whose title is translated as "The Chromophils in the Animal and Vegetable Kingdoms." The book itself has never been translated. By 1914 Tswett's brief, brilliant research career was essentially at an end. The German invasion of Poland in 1915 forced the Technical University to move to Moscow, and then to Nizhni Novgorod in 1916. Tswett's time was largely consumed with organizing the work of the botanical laboratories after each of these moves. In 1917 he accepted a position at the University at Yuryev in Estonia, but that too was overrun by the German army a year later. The university moved to Voronezh in 1918, but Tswett's health, never robust, failed quickly, and he died of a heart ailment at age forty-seven, on June 26, 1919.

Tswett's strength as a scientist lay in how well he understood both chemistry and botany. He had always been interested in the internal molecular structures of plants, often inquiring what their purpose might be, and the work he did on chlorophyll was one of his most important research efforts. He had long doubted the contention, which was widely accepted at the time, that chlorophyll was a compound that actually existed in plants. He decided this belief was the result of a misunderstanding; he hypothesized that chemists had been confused either because chlorophyll was combined nearly inseparably with other molecules within the leaf or because a compound recovered by a particular separation technique might in fact be an artifact of the technique. He was able to demonstrate all of these misunderstandings in the work of others, both by his deployment of the chemical separation methods of the time (fractional solution and precipitation, diffusion, differential solution) and by the adsorption methods he developed, culminating in chromatography.

"Adsorbent" means holding molecules on the surface of the material, not in the body, and chromatography is a process which employs substances which have this property. It is a separation technique in which a very finely powdered adsorbent material is held in a vertical tube or "column." The mixture to be separated is placed on the top of the column, dissolved in as small an amount of solvent as possible, so that it forms a narrow band of adsorbed mixture; then more solvent is allowed to flow through the column, top to bottom. The molecules in the mixture are more or less strongly held by the adsorbent; those weakly held are washed down the column most rapidly, and those strongly held move less rapidly. After a suitable development time, the components of the mixture separate into a series of bands spaced along the column. The plug of wet adsorbent is blown out of the column onto a plate, where the bands can be cut apart and the components recovered separately. As the mixtures separated in these early experiments were colored, and the bands absorbed light in the visible spectrum, Tswett named the process chromatography ("color-writing"), and the developed separation he called a chromatogram. Even though most mixtures are not colored, this terminology is retained; the components must be detected by some means other than the eye. Many sophisticated varieties of chromatography are in use today: paper, thin-layer, gas-liquid, and ion exchange, to name but a few. Still, Tswett's column method has not been totally displaced.

Tswett used this technique to demonstrate that chlorophyll indeed does not exist in the plant as a free molecule but is complexed with albumin. He named this complex "chloroglobin ," by analogy with the heme complex of the blood, hemoglobin. There was, however, widespread skepticism of his research methods, and this finding was sharply criticized. Tswett next analyzed the plant pigments themselves, which were understood at the time to be only two: green chlorophyll and yellow xanthophyll. Using not chromatography but the standard chemical methods of the time, he demonstrated that there are two chlorophylls: xanthophyll and carotene. This finding was hotly disputed, partly because chlorophyll passed the test of a single pure compound: it could be crystallized. Tswett was able to show that the "crystallizable chlorophyll" formed by lengthy extraction with hot ethanol was in fact another compound; it is known today as an ethyl ester formed by transesterification of one of chlorophyll's ester groups.

During the course of his pigment work Tswett had found that when he ground the plant leaves with powdered calcium carbonate to neutralize acids, all but carotene were adsorbed on the solid carbonate. He used this as a method to separate carotene. It is not clear that this led to his devising column chromatography, but once he had developed this technique he found that in addition to two chlorophylls there were four xanthophylls and, of course, carotene. These findings came to be accepted later, but mainly through the work of the German chemist Richard Willstätter.

The technique of column chromatography was not widely used in Tswett's lifetime, being regarded by his most vocal opponent, L. Marchlewski, as no more than a "filtration experiment." It was only later in the century that his work was reevaluated and his status as one of the originators, though probably not the sole inventor, of chromatography, was confirmed. This is his legacy today, although some would consider the plant pigment work to be at least as important.