GB/T 15555.4-1995 Determination of hexavalent chromium in solid wastes - Diphenylcarbazide spectrophotometric method
Some standard content:
National Standard of the People's Republic of China
Determination of chromium( V )-1,5-Diphenylcarbohydrazide spectrophotometric method1 Subject content and scope of application
GB/T15555.4—1995
1. This standard specifies the determination of hexavalent chromium in solid waste leachate using diphenylcarbonyl dithiocyanate spectrophotometry. 1.2 This standard applies to the determination of hexavalent chromium in solid waste leachate. 1.2.1 Determination range
The sample is 50mL, using 30mm pathlength colorimetric III, the detection limit of the method is 0.004mg/L. Using 10mm pathlength colorimetric blood, the upper limit of determination is 1.0mg/L.
1.2.2 Interference
The test solution is colored, turbid, or contains oxidizing, reducing substances and Organic matter and the like interfere with the determination. Iron content greater than 1.0 mg/L also interferes with the determination. Molybdenum and mercury interfere with the determination by forming complexes with the color developer, but the reaction is not sensitive under the color development acidity of the method. Vanadium concentration greater than 4.0 mg/L interferes with the determination, but it can fade on its own after 10 minutes of color development. 2 Principle
In an acidic solution, hexavalent chromium reacts with diphenylcarbonyl to form a purple-red complex. Spectrophotometric determination is performed at a maximum absorption wavelength of 540 nm.
3 Reagents
Unless otherwise specified, the reagents used in this standard are analytically pure reagents and distilled water or water of equivalent purity that meet national standards or professional standards;
3.1 Acetone (C,HO).
3.2 Sulfuric acid (H,SO), p=1.84 g/mL.
3.3 Phosphoric acid (H.PO,), p=1.69 g/mL. 3.4 Potassium dichromate (K,Cr2O,, high purity). 3.5 Diphenylcarbohydrazide (CH4N,O).
3.6 Sulfuric acid solution, 1+1:
Slowly add sulfuric acid (3.2) to an equal volume of water, stirring while adding, and use after cooling. 3.7 Phosphoric acid solution, 1+1:
Mix phosphoric acid (3.3) with an equal volume of water. 3.8 Potassium permanganate (KMnO), 4%.
3.9 Urea Solution, 20%:
Approved by the State Environmental Protection Administration on March 28, 1995, and implemented on January 1, 1996
GB/T15555.4—1995bzxZ.net
Dissolve 20g of urea [(NH,), CO2 in water and dilute to 100mL. 3.10 Sodium nitrite, 2%:
Dissolve 2g of sodium nitrite (NaNO2) in water and dilute to 100mL. 3.11 Chromium standard stock solution, 0.1000mgCr6+/mL: Weigh 0.2829g of potassium dichromate (3.4) dried at 120℃ for 2h, dissolve it in a small amount of water, transfer it into a 1000mL volumetric flask, dilute to the mark with water, and shake well.
3.12 Chromium standard solution, 1.00μg/mL. Pipette 5.0 mL of chromium standard stock solution (3.11) into a 500 mL volumetric flask, dilute to the mark with water, and shake well. Prepare freshly when needed. 3.13 Chromium standard solution, 5.00 μg/mL: Pipette 25.00 mL of chromium standard stock solution (3.11) into a 500 mL volumetric flask, dilute to the mark with water, and shake well. 3.14 Color developer 1:
Weigh 0.2 g of diphenylcarbohydrazide (3.5), dissolve in 50 mL of acetone (3.1), dilute to 100 mL with water, shake well, store in a brown bottle at low temperature.
3.15 Color developer 2:
Weigh 2.0 g of diphenylcarbohydrazide (3.5), dissolve in 50 mL of acetone (3.1), dilute to 100 mL with water, shake well, store in a brown bottle at low temperature.
Note: If the color of the color developer turns darker, it cannot be used. 4 Instruments
General laboratory instruments and
4.1 Spectrophotometer.
5 Steps
5.1 Sample preservation
Adjust the pH value of the leaching solution to 8 with sodium hydroxide. Determine within 24 hours. 5.2 Sample pretreatment
5.2.1 When there is no interference from reducing substances, organic matter, color, etc., the sample can be directly taken for determination. 5.2.2 When there are interfering substances, it can be treated according to the following steps before determination. 5.2.2.1 If the color of the sample affects the determination, it can be corrected as follows: Take another sample and determine the absorbance of the sample according to step (5.3) (except taking 2.0mL acetone instead of the color developer) with water as the reference. Deduct this color and correct the absorbance value.
5.2.2.2 Elimination of reducing substances
Take an appropriate amount of sample in a 50mL colorimetric tube as a test material, dilute with water to the mark after neutralization, add 4.0mL of color developer (3.15), shake well, let stand for 5 minutes, add 1.0mL of sulfuric acid (3.6), shake well, let stand for 10 minutes, and determine according to the steps (5.3.3). This can eliminate the interference of reducing substances such as Fe2-, SO, -2S, O3-2. It is also possible to separate trivalent chromium, oxidize the reducing substances with ammonium persulfate, and then determine. 5.2.2.3 Elimination of organic matter
First, separate the trivalent chromium with zinc hydroxide precipitation, and then use acidic potassium permanganate to oxidize and decompose the organic matter. Take 50.0mL of sample (hexavalent chromium not exceeding 10μg) in a 150mL conical flask, neutralize, put a few glass beads, add 0.5mL of sulfuric acid (3.6), 0.5mL of phosphoric acid (3.7), shake well, add 2 drops of potassium permanganate solution (3.8), if the purple-red color fades, add more potassium permanganate solution to keep the red color, heat and boil until the solution is about 20mL, cool and filter with medium-speed quantitative filter paper, and place in 50mL Wash the colorimetric tube with water several times, combine the washing liquid and the filtrate, add 1.0 mL of urea solution (3.9) to the colorimetric tube, shake, add one drop of sodium nitrite solution (3.10), shake well, and wait until the red color of the solution just fades. Wait for a while until all the bubbles in the solution are exhausted, transfer to a 50 mL colorimetric tube, dilute with water to the mark, add 2.0 mL of color developer (3.14), shake well, and measure according to step (5.3.3) after leaving for 10 minutes.
GB/T15555.4—1995
5.2.2.4 Elimination of oxidizing substances of hypochlorite Take an appropriate amount of sample in a 50mL colorimetric tube as the test material, dilute to the mark with water after neutralization, add 0.5mL of sulfuric acid (3.6), 0.5mL of phosphoric acid (3.7), 1.0mL of urea (3.9) and shake well, add sodium nitrite solution (3.10) drop by drop, shake while adding, and add 2.0mL of color developer (3.14) to completely eliminate the gas in the solution, and then measure according to the steps of (5.3.3). 5.3 Measurement
5.3.1 Take the sample of (5.2.1) or (5.2.2) in a 50mL colorimetric tube (the hexavalent chromium should not exceed 10μg), dilute to the mark with water after neutralization.
5.3.2 Add 0.5 mL of sulfuric acid (3.6) and 0.5 mL of phosphoric acid (3.7), shake well, add 2.0 mL of color developer (3.14), shake well, and let stand for 10 minutes. 5.3.3 Use a 10 or 30 mm pathlength cuvette to measure the absorbance at 540 nm with water as reference, subtract the absorbance of the blank test (5.4), and find the amount of hexavalent chromium from the calibration curve (5.5). 5.4 Blank test
Replace the sample with 50 mL of water and perform a blank test according to the determination steps (5.3). 5.5 Drawing of calibration curve
Add 0.00, 0.20, 0.50, 1.00, 2.00, 4.00, 6.00, 8.00, 10.00 mL of chromium standard solution (3.12) to 9 50 mL stoppered colorimetric tubes respectively, add water to the mark, develop color and measure absorbance according to steps (5.3.2) and (5.3.3), and draw a calibration curve with the absorbance minus the blank as the ordinate and the amount of hexavalent chromium (μg) as the abscissa. 6 Expression of results
The concentration c (mg/L) of hexavalent chromium in the leaching solution is calculated as follows: c=V
Where: m——the amount of hexavalent chromium in the sample obtained from the calibration curve, ug; V—the volume of the sample, mL.
7 Precision and accuracy
7.1 Please refer to GB7467-87 "Determination of hexavalent chromium in water - diphenylcarbonyl spectrophotometry". 7.2 The relative standard deviation of the average determination of 6 times of chromium slag leaching solution with a hexavalent chromium concentration of 185.8 mg/L in the room is 0.14%. For the double samples of the leaching solution with a hexavalent chromium content of 3.176 μg, 4.00 μg of standard sample was added to each sample, and the spiked recovery rates were 99.4% and 103.7%. 541
GB/T15555.4—1995
Appendix A
Notes
(reference)
When the concentration of hexavalent chromium in the sample is high, a chromium standard solution (3.15) can be used and measured with a 10mm optical path colorimetric III. The color developing acidity should be between 0.05 and 0.3 mol/L (1/2H, SO), and 0.2 mol/L is the best. The sample must be neutralized before measurement.
The glassware used should not be washed with potassium dichromate solution. The amount of color developer is generally controlled to be 1 mol of hexavalent chromium, and 1.5 to 2.0 mol of color developer is added. If phthalic anhydride is added when preparing the color developer, it can be stored in the dark for 30 to 40 days. The color developer turns orange and cannot be used.
Note: For the preparation method of the leaching solution, please refer to Appendix B of GB/T15555.1-1995 "Determination of Total Mercury in Solid Wastes by Cold Atomic Absorption Spectrophotometry". Additional Notes:
This standard was proposed by the Science and Technology Standards Department of the State Environmental Protection Administration. This standard was drafted by the China National Environmental Monitoring Center. The main drafters of this standard were Rui Kuisheng and Xing Shucai. This standard was entrusted to the China National Environmental Monitoring Center for interpretation. 542
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