Testing Method of Fe Element in Sodium Tungstate 1/2

(Note: the water referred following is single-distilled water, the reagent is secondary purity.)
1.Be ready with:
(1)Hydrochloric acid 1:1
(2)Ammonia hydroxide 1:1
(3)50% Citric acid aqueous solution
(4)10% Ethylene Diamine Tetraacetic Acid(EDTA) solution
(5)10% Hydroxylamine hydrochloride solution
(6)Buffer solution(PH:7-8): Mix 25ml 0.2M KH2PO4(13.61g soluble in 500ml water) and 46.1ml 0.1M NaOH, dilute to 100ml, adjust PH value by PH meter.
(7)0.2% Phenanthroline monohydrate solution: Dissolve 1.0g phenanthroline monohydrate in 500ml water(PH:7-8)
(8)Sodium tungstate solution: Adding 14.23g Na2WO4 into beaker with 50ml water, drop in 6N NaoH, after Na2WO4 dissolved completely, move the solution into 100ml volumetric flask, shake it up, WO3 concentration of solution is 100mg/ml.
(9)Fe standard solution: Put 1.0g pure ferric wire into 250ml beaker, add 50ml 1:1 hydrochloric acid, heat it until it dissolve completely, move to 100 ml volumetric flask. Dilute with water to 100ml. The current Fe=1mg/ml. Then dilute the solution into Fe=10ug/ml.
(10)PHs—2 acidimeter; 721 ultraviolet spectrophotometer.

2.Analytical procedure:
(1)Absorb a few ml of sodium tungstate solution(WO3 content is near 100mg) and Fe standard solution(Fe content is 5-20ug) into 100ml beaker, adding 8ml of 50% citric acid aqueous solution, adding water to clean the beaker wall until the volume of solution reaches 25ml, shake it up, heat it for 1-2min on the electric furnace.
(2)Adding 2ml of 10% EDTA solution, 2ml of 10% hydroxylamine hydrochloride solution, adjust PH value to 7 by NH3H2O (firstly coarse tuning by test paper, then adjust by PH meter).
(3)Add 5ml buffer solution. Put beaker in 60℃ water, then adding 2ml of 0.2% phenanthroline monohydrate solution. Keep it warm for 15min. Then pour into 50ml beaker and dilute with water to 50ml.
(4)When the wave length is 510nm, use 2cm cuvette to test its absorbance on 721 ultraviolet spectrophotometer.

3.Working curve：
(1)Absorb 5, 10, 15, 20, 30ug of 10ug/ml Fe standard solution in different 100ml beakers, adding 8ml of 50% citric acid aqueous solution and sodium tungstate solution(WO3 content is 100mg), the following steps is the same as analytical procedure. Then test its absorbance.
(2)Fe content is calculated by :Fe(mg/L)=γ/V x 10^-3
Among which:
γ——quantity of Fe(ug) from the tested solution which is obtained from working curve.
V——quantity of sample(L)

4. Note:
(1)When adding citric acid aqueous solution, the obtained solution must reach 25ml or more, the boiling time must be 1-2min, temperature of electric furnace should within a certain limit in case the solution will turn yellow and affect the testing result.
(2)When adding phenanthroline monohydrate solution, shake the beaker at the same time, control the adding speed, if it is too fast, there would be participants. If there is participants, adding ammonium solution to dissolve it and adjust PH value to 8 by 1:1 hydrochloric acid until the participants disappear. If the participants happens again, the sample needs to be modulated again.

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