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Vitamin C appears in your NCERT table as one line: ascorbic acid, citrus fruits and amla, scurvy. The person who first isolated it was not looking for a vitamin at all. He was trying to understand why some fruits turn brown. This post covers how Albert Szent-Györgyi found the substance, how it was proved to be vitamin C, why paprika mattered, and how you can measure vitamin C yourself with a titration.
Who was Albert Szent-Györgyi?
His Nobel facts page records that he was born in Budapest on 16 September 1893 and died at Woods Hole, Massachusetts, on 22 October 1986. His Nobel biography says he was wounded in the First World War, worked in Groningen from 1922 to 1926, went to Cambridge in 1927 as a Rockefeller Fellow under F. G. Hopkins, and took the chair of medical chemistry at Szeged in 1930. Later he discovered the muscle proteins actin and myosin.
He received the 1937 Nobel Prize in Physiology or Medicine "for his discoveries in connection with the biological combustion processes, with special reference to vitamin C and the catalysis of fumaric acid".
How did browning fruit lead to vitamin C?
His Nobel lecture tells the story. He was interested in the adrenal cortex, because in Addison's disease, when it fails, the skin turns brown, a little like a bruised apple. About half of all plants brown when damaged. He turned to the plants that do not, which contain an enzyme called peroxidase.
Peroxidase plus hydrogen peroxide turns benzidine blue at once. But with juice squeezed from these plants, the blue appeared after a delay of about a second. He traced the delay to a powerful reducing substance that kept reducing the oxidised dye until it was used up. Then, in his "little basement room in Groningen", he found the adrenal cortex contained a similar substance in large amounts.
At Cambridge he isolated it from adrenal glands and plants and showed its formula was C6H8O6. His 1928 paper in the Biochemical Journal reported this work on peroxidase systems and the adrenal cortex. A year's work with adrenals from American slaughterhouses gave him 25 g of crystals, which he called hexuronic acid. He gave half to Walter Haworth in Birmingham to work out its structure.
How was it proved to be vitamin C?
He had suspected the link from the start, but had no experience of vitamin tests. At Szeged a young American, J. L. Svirbely, joined him, convinced at first that hexuronic acid was not vitamin C. Their experiments, finished in the autumn of 1931, showed it was strongly antiscorbutic and that the anti-scurvy activity of plant juices matched their hexuronic acid content. They repeated the work before publishing in 1932 as Hexuronic acid as the antiscorbutic factor in Nature.
Then came the supply problem. Szeged was the centre of the Hungarian paprika industry. One evening he tested paprika and found it an extremely rich source. Before that season ended he produced more than half a kilogram of crystalline acid, and more than three kilograms the next year. With Haworth he renamed it ascorbic acid. He shared it with anyone who wanted to work on it, including his fellow 1937 laureates Haworth and Paul Karrer. Haworth's own Nobel lecture confirms the visit, the paprika and the new name. Our post on Walter Haworth and the ring structures of sugars covers the structure.
Worked example: measuring vitamin C with iodine
Haworth's lecture notes that ascorbic acid is oxidised reversibly by iodine, losing two hydrogen atoms in the first stage. That gives a 1:1 reaction you can use in a titration:
C6H8O6 + I2 → C6H6O6 + 2HI
These are sample numbers for illustration. A 25.0 mL sample of juice needs 12.0 mL of 0.0050 mol L⁻¹ iodine solution to reach the starch end point.
Moles of iodine: 0.0120 L × 0.0050 mol L⁻¹ = 6.0 × 10⁻⁵ mol.
Moles of ascorbic acid: also 6.0 × 10⁻⁵ mol, because the ratio is 1:1.
Mass: 6.0 × 10⁻⁵ mol × 176.12 g mol⁻¹ = 0.0106 g = 10.6 mg in 25.0 mL.
Per 100 mL: 10.6 × 4 = 42 mg.
Common mistakes to avoid:
Leaving volume in millilitres. Convert to litres before multiplying by concentration.
Using the wrong molar mass. Ascorbic acid, C6H8O6, is 176.12 g mol⁻¹, not 180 like glucose.
Testing old juice. Haworth noted that air with traces of copper destroys ascorbic acid, so juice left standing in air can read low.
Forgetting it is water soluble. The NCERT Biomolecules unit explains that water-soluble vitamins like C are excreted in urine and must be eaten regularly. Our post on vitamin classification and deficiency diseases covers the rest of that table.
To see the stoichiometry behind titrations worked through, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
What can a student learn from Szent-Györgyi?
Follow the odd detail. The delay before the blue colour was the clue.
Look at what is around you. Paprika was in the market outside his laboratory.
Share your material. By handing out ascorbic acid freely, he let others finish the structure and the synthesis.
Collaborate with sceptics. Svirbely arrived doubting the idea, which made the test more convincing.
Try it now: if 20.0 mL of lemon juice needs 15.0 mL of 0.0050 mol L⁻¹ iodine, how many milligrams of vitamin C are in 100 mL?
