Recent developments in polarography of vitamins are reviewed. Polarographic data of some compounds related to thiamine are summarized in Table I. Thiol type thiamine shows anodic waves accompanied with adsorption waves. Thiols react with Hg⁺, Ag⁺, p-chloromercuribenzoate, etc, and are oxidized to disulfides at platinium electrode. Disulfides are reduced to form two thiols at DME and hydro lysed to produce thiol and sulfinic acid. Ammonium type thiamine reacts with Hg⁺, BiJ₄^-, Reineckate, etc. Pyrimidine and thiazole rings of thiamine and its homologues are reduced at DME and the reduction products, amines, show a catalytic hydrogen wave. Thiamine and thiazolium salts show maximum waves in a buffer solution containing a cobalt salt. Riboflavin, FMN, FAD and other isoalloxazines give reversible a 2-electron reduction wave accompanied with an adsorption wave. (Table II) Folic acid and its homologues give 3 steps of 2-electron reduction wave in acid and the first step in alkali. (Table III). Their final reduction products are 6-methyl-5, 6, 7, 8-tetrahydropteridine derivatives and p-aminobenzoylglutamic acid. Pteridine de rivatives are reduced to dihydropteridines at DME and some of them are reduced to tetrahydropteridines. (Table IV) The polarographic behaviour is modified by adsorption, dissociation, hydration and tautomerism. Leucovorin is determined by an anodic wave of 10-formyltetrahydropteroyl-glutamic acid produced by acid and alkali treatment of leucovorin. Pyridoxine, pyridoxamine and pyridoxal give a reduction wave in an unbuffer solution. Pyridoxal is reduced to pyridoxine in alkali at DME, but its hydrated form in acid is not. Vitamin B₁₂ homologues give a catalytic hydrogen wave and reduction waves of cobalt complex. (B₁₂ : Co^III→Co^IT, B_12a : Co^III→Co^II→Co^I, B_12r : Co^II→Co^I, Co^II→Co^II). Niacin gives a catalytic hydrogen wave and reduction waves in pH>9. Niacin amide gives reduction waves even in alkali. Ascorbic acid is oxidized to dehydroascorbic acid which is inactivated by hydration. Second oxidation wave of ascorbic acid in alkali is assumed to be due to the oxidation of enol type 2, 3-diketogulonic acid to 2, 3, 4-triketo-gulonic acid. Flavones and flavanones give a reduction wave caused by 2-electron reduction of carbonyl. Chalcones give two reduction waves. (Table V). α-Lipoic acid is reduced to dihydrolipoic acid (dithiol) by 2-electron reduction at DME. Q-Lipoic acid gives a 4-electron reduction wave and is easily decomposed by alkali. Adsorption phenomena of the Lipoic acid are observed in their polarograms. Carotene and vitamine A are determined by the anodic wave of their iodinated derivatives. Tocopherol gives an anodic wave in positive potential, and its oxidation product, tocopherol quinone, gives a reduction wave. Naphthoquinone derivatives in cluding vitamin K give a reversible 2-electron reduction wave. Decomposition of menadione and its NaHSO₃ adduct, and hydrolysis of hydroquinone esters are studied polarographically.

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A marked tendency to treat electrochemical problems in non-aqueous media has reappeared lately, as the more essential and available developments are expected with the use of another material in exchange for water as solvent . The employment of the polarographic method is also of great advantage to those investigations. In the present description, the polarographic method in organic solvents is arranged on the fundamental procedure and the referable reports in recent years are introduced. The contents are summarized as follows. 1. Preface 2. Favourable Solvents (1) Acetonitrile (2) Acetic acid (3) Formic acid (4) Acidamides (5) Other solvents (6) Mixed solvents 3. Refinement of Solvents 4. Electrolytic Solution (1) Supporting electrolyte and Cell resistance (2) Preparation of electrolyticsolution (3) Removal of dissolved oxygen 5. Troubles on Electrode (1) Dropping mercury electrode and Polarographic maxima ; Rotating platinum electrode (2) Reference electrode (3) Disproporn tionation of mercurous salts 6. Reference Electrodes with Organic Solvent (1) Calomel electrode (2) Silver-silver chloride electrode (3) Other reference electrodes (4) Quality test of reference electrode 7. Electrode Potential in Non-aqueous Solution 8. Liquid Junction Potential ; Method of Junction 9. Polarography with Organic Solvents (1) Limiting diffusion current (2) Half-wave potential and others 10. Conclusion

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The polarographic determination of amino acids as copper complex has alreadybeen introduced by Jones, Martin and others : This method is based on the factthat soluble copper-amino acid complex is formed by the addition of the copper phos phate suspension into amino acid solution. However, considerable errors are en countered in this method. The reason for this may be attributed to a relatively high solubility of copper phosphate and for lack of reproducibility, because they utilize such reaction as between liquid and solid. Such reaction process as mentioned above, there fore, should be avoided in order to reduce the errors. By thorough investigation the authors found a superior method which is employed a liquid-liquid reactoin. This method is used the solution of copper instead of the copper phosphate suspension, and then the pH of the solution is adjusted to 9.0, the precipitate is filtered off and the concentration of copper ion in the filtrate is determined polarographically.

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