Antimony chemical analysis method - Determination of arsenic by molybdenum blue spectrophotometry
This standard complies with GB467-78 "General Principles and General Provisions of Chemical Analysis Methods for Metallurgical Products". This standard is applicable to the determination of arsenic in antimony. Determination range: 0.01%-0.6%
Method Summary: The sample is dissolved with sulfuric acid. In not less than 9N hydrochloric acid solution, arsenic trichloride is separated from the matrix and other coexisting impurities by benzene extraction. Then, arsenic is back-extracted with water and oxidized to pentavalent arsenic. Ammonium molybdate and hydrazine sulfate are added to generate arsenic molybdenum blue, and its absorbance is measured at 660nm with a spectrophotometer.
The determination is not interfered with by the presence of 1 mg each of iron, copper, and lead in the aliquot of test solution, and the selenium content in the sample is not more than 0.1%.
Analysis Steps
1. Weigh 0.2 g of the sample into a 150 ml conical flask, and perform a blank test along with the sample.
2. Moisten the sample with a small amount of water, add 8 ml of concentrated sulfuric acid, and heat on a hot plate. Dissolve the sample to clarity while keeping the solution near boiling. Remove and cool, add 5 ml of water, and cool to room temperature. (Note: Cool the solution to room temperature to avoid volatilization loss of arsenic trichloride due to high temperature when adding hydrochloric acid.)
3. Add 30 ml of concentrated hydrochloric acid, transfer the solution to the first 125 ml separatory funnel, add 30 ml of benzene, shake and extract for 1 minute, and let it stand for layering.
4. Transfer the aqueous phase to a second separatory funnel containing 15 ml of benzene, shake and extract for 1 minute, let it stand for layering, and discard the aqueous phase.
5. Combine the benzene layers in the first separatory funnel. Rinse the neck and ground glass stopper of the first separatory funnel with 5 ml of (3:1) hydrochloric acid, shake for half a minute, let it stand for layering, and discard the aqueous phase. Rinse again with 5 ml of (3:1) hydrochloric acid, let it stand for 2 minutes, and separate the aqueous phase as completely as possible.
6. Add 20 ml of water to the separatory funnel for back-extraction, shake for half a minute, let it stand for layering, and transfer the aqueous phase to a 50 ml volumetric flask. Add 15 ml of water, shake for half a minute, let it stand for layering, and combine the aqueous phase in the volumetric flask.
7. Add 1 drop of phenolphthalein solution (0.1%), neutralize with sodium hydroxide solution (30%) to red, then add sulfuric acid (1:20) until the red color just disappears. Add iodine solution (0.5%) until the solution is yellow and 0.1 ml excess, and let it stand for 3 minutes.
8. Add sulfite (1:2) to decolorize the yellow, add 2 ml of ammonium molybdate solution (1.5%), and mix well. Then add 2 ml of hydrazine sulfate solution (0.05%), mix well. Heat in a boiling water bath for 7 minutes, remove and cool to room temperature, dilute with water to the mark, and mix well.
9. Transfer a portion of the solution to a 3 cm cuvette, use the sample blank as a reference, measure the absorbance at 660 nm with a spectrophotometer, and find the corresponding arsenic content from the working curve.
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