Volumetric micro- and submicro-determination of thiosulphate with 24-fold amplification

Abstract

* Present address: 995 Cranbrook Court No. 206, Davis, CA95616, USA Optimum working conditions have been studied in detail and resulted in the following instruction: Introduce 0 . 5 2 ml of 0.0005 N thiosulphate solution (28 112 lag of $20~ -) into a 50 ml conical flask, add ca. 5 ml of water, I ml of potassium periodate solution (1 g in 300 ml H20), and 5 drops (ca. 0.2ml) of 0.05M borax solution, heat on a small flame and keep at boiling temperature for 5 min. Cool, add 1 ml of 25 % ammonium molybdate tetrahydrate solution, 3 ml of buffer solution (pH 3; 110 ml of glacial acetic acid + 40 ml of 0.2 M sodium acetate solution) and 1 ml of 10 % freshly prepared potassium iodide solution, stopper the flask and leave aside for 1 rain. Titrate the iodine liberated with 0.005 N thiosulphate titrant using starch as usual. Carry out a blank experiment and calculate the content. I ml of thiosulphate titrant is equivalent to 23.361ag of thiosulphate analysed. For SaO32amounts between 0.56 and 2.24mg use 20 ml of periodate and 1.5 ml of borax solutions. After boiling for 5 min, cool, add 20 ml of molybdate, 7 ml of buffer and 10 ml of iodide solution. Use 0.1 N thiosulphate solution as titrant. 1 ml corresponds to 0.467 mg of $20~-.