Water Quality - Determination of Chromium (VI) - 1, 5 Diphenylcarbohydrazide Spectrophotometric Method
水质 六价铬的测定
二苯碳酰二肼分光光度法
1 Application Scope
1.1 This standard is applicable to determination of surface water and industrial waste water.
1.2 Determination scope
Volume of the test portion is 50mL. Cuvette with 30mm optical path is used, the minimum detectable amount of this method is 0.2μg Chromium (VI), and the minimum detectable concentration is 0.004mg/L; and the detectable upper concentration limit is 1.0mg/L.
1.3 Interference
When the iron content is greater than 1mg/L, it will show yellow. molybdenum (VI) and mercury (Hg) also react with color reagent to generate colored compound, however, under the color rendering acidity of this method, the reaction is insensitive, and the molybdenum and mercury (Hg) with concentration reaching 200mg/L will not interfere determination; while for vanadium, when its content is greater than 4mg/L, the color rendering will be interfered. 10min after reaction between vanadium and the color reagent, the color may fade automatically.
2 Principle
Chromium (VI) will react with 1, 5 diphenylcarbohydrazide to generate aubergine compound in acid solution, and the spectrophotometric determination will be conducted at 540nm wave length.
3 Reagent
Unless otherwise stated, analytical reagent conforming with national standards or professional standards and distilled water or water with equivalent purity shall be adopted during the determination, and moreover, no reagent shall contain chromium.
3.1 Acetone.
3.2 Sulfuric acid
3.2.1 1+1 sulfuric acid solution.
Sulfuric acid (H2SO4, ρ=1.84g/mL, guaranteed reagent) is added to water of the same volume slowly and mixed uniformly.
3.3 phosphoric acid: 1+1 phosphoric acid solution.
Phosphoric acid (H3PO4, ρ=1.69g/mL, guaranteed reagent) is mixed with water of the same volume.
3.4 Sodium hydroxide: 4g/L sodium hydroxide solution.
1g sodium hydroxide (NaOH) is dissolved into water and diluted to 250mL.
3.5 Zinc hydroxide coprecipitator
3.5.1 Zinc sulfate: 8% (m/V) zinc sulfate solution.
8g zinc sulfate(ZnSO4·7H2O) is weighed to dissolve in 100mL water.
3.5.2 Sodium hydroxide: 2% (m/V) solution
2.4g sodium hydroxide is weighed to dissolve in 120mL water.
The two kinds of solution in Articles 3.5.1 and 3.5.2 are mixed.
3.6 Potassium permanganate: 40g/L solution.
4g potassium permanganate (KMnO4) is weighed and dissolved in water while heated and stirred, and then it is diluted until 100mL.
3.7 Chromium standard stock solution.
0.2829±0.0001g potassium dichromate (K2Cr2O7, guaranteed reagent), dried for 2h at 110℃, is weighed, and it is dissolved with water before transferred into 1000mL volumetric flask, diluted with water to the mark line, and shaken well. 1mL this solution contains 0.10mg Chromium (VI).
3.8 Chromium standard solution.
5.00mL chromium standard stock solution (Section 3.7) is pipeted to 500mL volumetric flask, and is diluted with water to the mark line and shaken well. 1mL this solution contains 1.00μg Chromium (VI), and it is prepared on the using day.
3.9 Chromium standard solution.
25.00mL chromium (Cr) standard stock solution (Section 3.7) is pipeted and placed in a 500mL volumetric flask, and then diluted with water to the scale, and shaken well.1mL this solution contains 5.00μg Chromium (VI), and it is prepared on the using day.
3.10 Urea: 200g/L urea solution.
20g urea [(NH2)2CO] is dissolved into water and diluted until 100mL.
3.11 Sodium nitrite: 20g/L solution.
2g sodium nitrite (NaNO2) is dissolved into water and diluted until 100mL.
3.12 Color reagent (I).
0.2g 1, 5 diphenylcarbohydrazide (C13H14N4O) is weighed and dissolved into 50mL acetone (Section 3.1), and then diluted with water to 100mL and shaken well, later, it is stored in brown bottle and places in refrigerator. It cannot be used when color becomes deep.
3.13 Color reagent (II).
2g 1, 5 diphenylcarbohydrazide is weighed and dissolved into 50mL acetone (Section 3.1) before diluted with water to 100mL and shaken well. It is then stored in brown bottle and placed in refrigerator. It can not be used if its color gets deep.
Note: color reagent (I) may also be prepared according to the following method: 4.0g phthalate anhydride (C6H4O) is weighed and added into 80mL ethanol. It is stirred to dissolve (it may be slightly warmed by water bath where necessary), before 0.5g 1, 5 diphenylcarbohydrazide is added, then, it is diluted with ethanol until 100mL. This solution can be preserved for 6 months at dark place, and it shall be shaken well immediately after color reagent is added at use, so as to avoid reduction of Chromium (VI).
4 Apparatus
General laboratory apparatus and:
4.1 Spectrophotometer.
Note: inner wall of all glass ware must be smooth and clean, so as to avoid adsorption of chromium ion. Potassium dichromate washing liquor shall not be used for the washing, while nitric acid, sulfuric acid mixed solution or synthetic detergent can be used, however, it shall be rinsed clear after washing.
5 Sampling and Sample
Laboratory sample shall be collected with glass bottle, and sodium hydroxide is added to regulate its pH value close to 8 during collecting. The pH shall be determined as soon as possible after collection and in case of storage, it shall not be longer than 24h.
1 Application Scope
2 Principle
3 Reagent
4 Apparatus
5 Sampling and Sample
6 Procedures
7 Result Expression
Additional Explanation
Water Quality - Determination of Chromium (VI) - 1, 5 Diphenylcarbohydrazide Spectrophotometric Method
水质 六价铬的测定
二苯碳酰二肼分光光度法
1 Application Scope
1.1 This standard is applicable to determination of surface water and industrial waste water.
1.2 Determination scope
Volume of the test portion is 50mL. Cuvette with 30mm optical path is used, the minimum detectable amount of this method is 0.2μg Chromium (VI), and the minimum detectable concentration is 0.004mg/L; and the detectable upper concentration limit is 1.0mg/L.
1.3 Interference
When the iron content is greater than 1mg/L, it will show yellow. molybdenum (VI) and mercury (Hg) also react with color reagent to generate colored compound, however, under the color rendering acidity of this method, the reaction is insensitive, and the molybdenum and mercury (Hg) with concentration reaching 200mg/L will not interfere determination; while for vanadium, when its content is greater than 4mg/L, the color rendering will be interfered. 10min after reaction between vanadium and the color reagent, the color may fade automatically.
2 Principle
Chromium (VI) will react with 1, 5 diphenylcarbohydrazide to generate aubergine compound in acid solution, and the spectrophotometric determination will be conducted at 540nm wave length.
3 Reagent
Unless otherwise stated, analytical reagent conforming with national standards or professional standards and distilled water or water with equivalent purity shall be adopted during the determination, and moreover, no reagent shall contain chromium.
3.1 Acetone.
3.2 Sulfuric acid
3.2.1 1+1 sulfuric acid solution.
Sulfuric acid (H2SO4, ρ=1.84g/mL, guaranteed reagent) is added to water of the same volume slowly and mixed uniformly.
3.3 phosphoric acid: 1+1 phosphoric acid solution.
Phosphoric acid (H3PO4, ρ=1.69g/mL, guaranteed reagent) is mixed with water of the same volume.
3.4 Sodium hydroxide: 4g/L sodium hydroxide solution.
1g sodium hydroxide (NaOH) is dissolved into water and diluted to 250mL.
3.5 Zinc hydroxide coprecipitator
3.5.1 Zinc sulfate: 8% (m/V) zinc sulfate solution.
8g zinc sulfate(ZnSO4·7H2O) is weighed to dissolve in 100mL water.
3.5.2 Sodium hydroxide: 2% (m/V) solution
2.4g sodium hydroxide is weighed to dissolve in 120mL water.
The two kinds of solution in Articles 3.5.1 and 3.5.2 are mixed.
3.6 Potassium permanganate: 40g/L solution.
4g potassium permanganate (KMnO4) is weighed and dissolved in water while heated and stirred, and then it is diluted until 100mL.
3.7 Chromium standard stock solution.
0.2829±0.0001g potassium dichromate (K2Cr2O7, guaranteed reagent), dried for 2h at 110℃, is weighed, and it is dissolved with water before transferred into 1000mL volumetric flask, diluted with water to the mark line, and shaken well. 1mL this solution contains 0.10mg Chromium (VI).
3.8 Chromium standard solution.
5.00mL chromium standard stock solution (Section 3.7) is pipeted to 500mL volumetric flask, and is diluted with water to the mark line and shaken well. 1mL this solution contains 1.00μg Chromium (VI), and it is prepared on the using day.
3.9 Chromium standard solution.
25.00mL chromium (Cr) standard stock solution (Section 3.7) is pipeted and placed in a 500mL volumetric flask, and then diluted with water to the scale, and shaken well.1mL this solution contains 5.00μg Chromium (VI), and it is prepared on the using day.
3.10 Urea: 200g/L urea solution.
20g urea [(NH2)2CO] is dissolved into water and diluted until 100mL.
3.11 Sodium nitrite: 20g/L solution.
2g sodium nitrite (NaNO2) is dissolved into water and diluted until 100mL.
3.12 Color reagent (I).
0.2g 1, 5 diphenylcarbohydrazide (C13H14N4O) is weighed and dissolved into 50mL acetone (Section 3.1), and then diluted with water to 100mL and shaken well, later, it is stored in brown bottle and places in refrigerator. It cannot be used when color becomes deep.
3.13 Color reagent (II).
2g 1, 5 diphenylcarbohydrazide is weighed and dissolved into 50mL acetone (Section 3.1) before diluted with water to 100mL and shaken well. It is then stored in brown bottle and placed in refrigerator. It can not be used if its color gets deep.
Note: color reagent (I) may also be prepared according to the following method: 4.0g phthalate anhydride (C6H4O) is weighed and added into 80mL ethanol. It is stirred to dissolve (it may be slightly warmed by water bath where necessary), before 0.5g 1, 5 diphenylcarbohydrazide is added, then, it is diluted with ethanol until 100mL. This solution can be preserved for 6 months at dark place, and it shall be shaken well immediately after color reagent is added at use, so as to avoid reduction of Chromium (VI).
4 Apparatus
General laboratory apparatus and:
4.1 Spectrophotometer.
Note: inner wall of all glass ware must be smooth and clean, so as to avoid adsorption of chromium ion. Potassium dichromate washing liquor shall not be used for the washing, while nitric acid, sulfuric acid mixed solution or synthetic detergent can be used, however, it shall be rinsed clear after washing.
5 Sampling and Sample
Laboratory sample shall be collected with glass bottle, and sodium hydroxide is added to regulate its pH value close to 8 during collecting. The pH shall be determined as soon as possible after collection and in case of storage, it shall not be longer than 24h.
Contents of GB 7467-1987
1 Application Scope
2 Principle
3 Reagent
4 Apparatus
5 Sampling and Sample
6 Procedures
7 Result Expression
Additional Explanation
