First, the reagent
Iodine starch absorption solution, 0.05%, 0.5 g starch, add a little water in a beaker to make a paste, add 100 ml of boiling water, stir, and cool. Add 900 ml of water and add the iodine standard solution until it is ready to be blue (should be freshly prepared).
Arsenic trioxide standard solution, weighed reference trioxide 0.5000 g, dissolved in 10 ml of 1N sodium hydroxide solution. Add 1 drop of phenolphthalein indicator and neutralize with 1N hydrochloric acid. Transfer the solution to a 500 ml volumetric flask, dilute to the mark with water, and shake well. 1 ml of this solution contains 1 g of arsenic trioxide.
Iodine standard solution, 0.01 N, weigh 2.5 g of iodine and 20 g of potassium iodide, add a small amount of water and stir until completely dissolved, dilute to 2000 ml, and store in a brown bottle.
After calibrating the iodine standard solution, 10 ml of the arsenic trioxide standard solution was taken and placed in a 125 ml Erlenmeyer flask. Add 50 ml of 6% sodium bicarbonate solution, 1 ml of 0.5% starch solution, titrate to blue with iodine standard solution, and make a blank test.
N=W/(V×0.04946)
T=N×0.01603
The equivalent concentration of the N-iodine standard solution;
Weight of W-arsenic trioxide (g);
V-titration consumes the number of milliliters of iodine standard solution;
Titration of sulfur to T-iodine standard solution (g/ml);
0.04946 - milliequivalents of arsenic trioxide;
0.01603 - milliequivalents of sulfur.
Second, the analysis procedures
Weigh 0.5 g of the sample and place it in a porcelain boat pre-plated with 0.5 g of silica sand. Stir well and cover the upper part with a layer of silica sand.
40-50 ml of the absorption liquid was added to the absorption tube, and the porcelain boat containing the sample was pushed into a porcelain tube which had been heated to 1250°, and quickly stoppered. Pass air (or carbon dioxide) to make 2-3 bubbles per second. Due to the action of sulfur dioxide, the blue color of the absorption liquid begins to decrease, and the iodine standard solution should be added dropwise at any time to keep the solution blue. When the fading speed of the solution is slowed down, the gas flow can be appropriately increased, and the sulfur dioxide in the porcelain tube is completely discharged, and the titration is continued, and the blue color is unchanged within 1 minute, which is the end point. This method applies to the determination of <1% sulfur.
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