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Method for analysis of calcium metal - The determination of chlorine content by chloride - Selective electrode
1 Subject content and applicable scope
This standard describes the determination theory of chlorine in calcium metal, and specifies the analytical procedure, result calculation and method precision.
It is applicable to the chlorine in calcium metal with determination range of 300 to 5 000μg/g. The determination will not be interfered if the impurity elements of chromium, iron, aluminum, nickel, manganese and silicon are 1mg each, copper 4mg and magnesium 6mg.
2 Method summary
After hydrolysis, the specimen is converted into nitrate, sodium nitrate solution is used as ionic strength agent, then the chlorine content is directly determined by chloride-selective electrode under the conditions of pH 2~7.
3 Reagents
Unless otherwise specified, analytical reagents complying with the national or professional standards shall be used during analysis. The water used is deionized water or distilled water whose potential is less than 270mV.
3.1 Sodium nitrate solution: 5mol/L.
3.2 Nitric acid: guaranteed reagent with density of 1.42g/cm3.
3.3 Nitric acid solution(1+1): prepared with nitric acid (3.2).
3.4 Nitric acid solution 5%(V/V) : prepared with nitric acid (3.2).
3.5 Sodium hydroxide: guaranteed reagent.
3.6 Sodium hydroxide solution 20% (m/V): prepared with sodium hydroxide (3.5).
3.7 Sodium hydroxide solution 5% (m/V): prepared with sodium hydroxide (3.5).
3.8 Potassium nitrate solution: 1mol/L.
3.9 Phenolphthalein ethanol solution: 0.1% (mV).
3.10 Saturated potassium chloride solution
3.11 Matrix calcium solution
Weigh out 125.0g calcium carbonate of guaranteed reagent into a 300mL beaker, moisten it with water, slowly add nitric acid (3.2) to dissolve it, cool it, transfer it to a 500mL volumetric flask, dilute to the scale with water, and shake well. The calcium content in the solution is 1.000g/10mL.
3.12 Chlorine standard solution
3.12.1 Weigh out 1.648 4g guaranteed reagent of sodium chloride which has been burned at 500~600℃ for 40-50min in advance into a 100mL breaker, add water to dissolve it and transfer to a 1 000mL volumetric flask, dilute to the scale with water, and shake well. The chlorine content in the solution is 1.0g/mL.
3.12.2 Pipette 50.0mL of chlorine standard solution (3.12.1) to a 500mL volumetric flask and dilute to the scale with water, then shake well. The chlorine content in the solution is 100.0μg/mL.
4 Instrument
4.1 Acidometer or digital ionometer with accuracy no more than 1mV.
4.2 Chloride-selective electrode with linear determination range from 10-1~5×10-5mol/L.
4.3 Calomel reference electrode (double salt bridge) with 1mol/L of potassium nitrate solution that is replaced daily added to the outer sleeve.
4.4 Magnetic stirrer
4.5 The stirrer is about 20mm in length and 2mm in diameter. The iron core stirrer is sealed with polyethylene.
5 Analytical procedure
5.1 Electrode preparation
Before the test, soak the electrode in the water and wash it until the potential is less than -270mV, then put it into the specimen solution with chlorine content of 500μg/50mL, activate for 10~15min, and clean for later use.
5.2 Plotting of working curve
In a series of 50mL volumetric flasks, add 10.0mL matrix calcium solution (3.11) respectively, 0μg, 300μg, 500μg, 1 000μg, 3 000μg and 5 000μg of chlorine standard solutions (3.12.1 or 3.12.2), and then 20mL sodium nitrate solution (3.1) and 1 drop of phenolphthalein solution (3.9); use sodium hydroxide solution (3.6 and 3.7) to adjust the specimen solution to red, and then add nitric acid solution (3.4) dropwise upon the red just disappears. Dilute to the scale with water and shake well. Take part of the specimen solution into 50mL beakers separately, insert chlorine electrode (4.2) and saturated calomel reference electrode (4.3), add stirrer (4.5) to stir for 30s, let stand for 2min, read the equilibrium potential value (E) on acidimeter or ionmeter (4.1), and plot E-logCCl- working curve on semilog coordinate paper.
5.3 Sample analysis
5.3.1 Preparation for specimen solution
Weigh out 5.000g of calcium metal sample, accurate to 0.001g, place it in a 200mL tall beaker, cover it with watch glass, slowly add about 15mL of water to convert the solution into calcium hydroxide, drop 35mL of nitric acid solution (3.3), and stir to dissolve the precipitate completely (if the sample is insoluble, it can be dissolved by heating at low temperature on an electric furnace). After cooling, transfer the solution to a 50mL volumetric flask, dilute to the scale with water and shake well.
1 Subject content and applicable scope
2 Method summary
3 Reagents
4 Instrument
5 Analytical procedure
6 Calculation of analysis result
7 Method precision
