Some standard content:
1 Scope of application
National Standard of the People's Republic of China
Natural rubber latex -Determination of copper content
UDC 678.031
: 678.012
GB 8295—87
This standard adopts the international standard ISO1654-1971 "Raw rubber and latex - Determination of copper". This standard specifies the method for determining a small amount of copper in natural latex. This method is only applicable to natural latex from Hevea brasiliensis, not to compound latex or vulcanized latex.
2 Reference standards
GB8290—87 "Sampling of natural concentrated latex". GB8298—87 "Determination of total solid content of natural concentrated latex". 3 Sampling
Sampling shall be carried out in accordance with the method specified in GB8290. 4 Method Summary
The latex is dried to form a total solid, then ashed in a high-temperature furnace, dissolved with acid, and the copper element in it is converted into an inorganic salt form in the solution, so that the copper ion reacts with sodium diethyldithiocarbamate to form a complex, and then extracted with butyl acetate for colorimetric determination. 5 Instruments
General instruments for analysis and testing, as well as
5.1 High-temperature furnace can maintain 500~700±20℃. 5.272-1 type spectrophotometer, colorimetric trough optical path length 10~20mm. 6 Reagents
Purity requirements are all above analytical grade, and water quality requires the use of twice distilled water. 6.1 Nitric acid and hydrochloric acid mixed acid solution, the volume ratio is as follows, and the solution should be clear and colorless after preparation. Nitric acid: hydrochloric acid: water = 1:2:3.
6.21:20 sulfuric acid solution.
6.31:1 ammonium hydroxide solution.
6.40.1% cresol red indicator solution: Dissolve 0.1g cresol red in 50mL ethanol (95%) and dilute to 100mL with water. 6.510% disodium EDTA solution: Dissolve 10g disodium ethylenediaminetetraacetic acid in 100mL water. 6.620% ammonium citrate solution: Dissolve 40g citric acid in 160mL water, add 4 drops of cresol red indicator solution, neutralize with ammonium hydroxide solution, and continue to add 1:1 ammonium hydroxide solution to adjust the pH to about 9 (i.e., just purple-red, yellow when below 9), add water to 200mL, transfer the solution to a 250mL separatory funnel, add 4mL of ethyl: sodium thiocarbamate solution and 10ml of butyl acetate, shake vigorously for 3min, and let stand to separate. Open the piston and put the lower ammonium citrate phase into another 250mL separatory funnel. The Ministry of Agriculture, Animal Husbandry and Fisheries of the People's Republic of China approved on July 10, 1987 92
Implementation on June 1, 1988
GB 8295-87
Discard the butyl acetate phase, add 10mL of butyl acetate to the ammonium citrate phase, shake vigorously for 3 minutes, let stand to separate, then separate the ammonium citrate phase, filter with dry filter paper, and remove the residual drops of butyl acetate left in the ammonium citrate phase. 6.7 Copper standard solution: Weigh 0.393g of copper sulfate containing five crystal waters, put it into a 150mL beaker, add 100mL of water to dissolve, and add 3mL of concentrated sulfuric acid. Transfer the solution to a 1000mL volumetric flask, dilute to the mark with water, shake well, and the original solution is obtained. Use a pipette to draw 10mL of the original solution, put it into a 100mL volumetric flask, and dilute to the mark with water. This solution contains 10 μg/mL of copper and should be prepared as is.
7 Preparation of standard working curve
Use a microburette to take 1mL of copper standard solution containing 10ug copper respectively, and put 0, 0, 25, 0.50, 0.75, 1.00, 1.25, and 1.50mL into 7 60mL separatory funnels respectively, and add one drop of 0.1% cresol red indicator, 5mL of 20% ammonium citrate solution, and 2mL of 10% disodium EDTA solution in turn, adjust the pH value to slightly purple with 1:1 ammonia water, and adjust the solution volume to about 20mL with water, add 2mL of 0.1% sodium diethyldithiocarbamate solution, and then dilute the solution with water to 25mL, shake well, add 10mL of butyl acetate, shake vigorously for 3min, let stand for stratification, discard the aqueous phase, add 5mL of 1:20 sulfuric acid solution, shake vigorously for 1min, discard the aqueous solution, and filter into a 10mL brown volumetric flask with filter paper. Use a 10mm colorimetric cell and a wavelength of 435nm to measure its transmittance, convert it into optical density, subtract the blank optical density, use the optical density as the ordinate and the milliliters of the copper standard solution as the abscissa, and draw a straight line. This straight line is the standard working curve. 8 Operation steps
Cut about 10g of uniform total solid sample strips (about 1-2mm in diameter), store in a desiccator with silica gel for 24 hours, take out and weigh (accurate to 1mg), wrap the sample with a quantitative filter paper with a diameter of 150mm and place it in a 50mL crucible, cover it and move it into a high-temperature furnace, slowly increase the temperature for ashing, initially adjust the control temperature to 220-250℃, then increase the temperature by 20℃ every half an hour, and then increase the temperature by 50℃ every half an hour after 450℃, until 550-600℃ is maintained for 4-8 hours, until the ash content is colored without black spots. Turn off the high-temperature furnace and wait until it cools to below 200℃ and then take out the crucible. After cooling, add 10 mL of mixed acid solution (6.1), heat it on a steam bath or electric sand bath until it boils slightly (be careful not to splash it), until the solution turns from yellow to clear, add 15 mL of distilled water, continue heating for 15 minutes, remove it and cool it slightly, pour the solution into a 50 mL volumetric flask, and dilute it to the scale for use. Take 10 mL of the test solution and perform colorimetric determination according to the same procedure as making the standard working curve. Make 3 parallel determinations for each sample and make a blank control.
9 Calculation of copper content
According to the measured transmittance, convert it into optical density, subtract the optical density of the blank, and calculate the milliliter number V equivalent to the copper standard solution from the standard working curve. Calculate the copper content in the sample according to the following formula, in mg/kg total solids. Copper content, mg/kg total solids = -5·V.rm
Where: V—milliliter number of copper standard solution equivalent to the sample; copper content of the copper standard solution, μg/mL, total solid mass of the sample, g.
Each sample is measured three times, and the difference between the result and the average value should be less than 0.4 units, and then the average value is taken. Note: In order to obtain sufficient accuracy, the transmittance should be between 30% and 80%. If the copper content is particularly high or low, the colorimetric cell with different light path lengths and corresponding conditions should be replaced. 93
Additional notes:
This standard is under the jurisdiction of the Agricultural Reclamation Bureau of the Ministry of Agriculture, Animal Husbandry and Fisheries, GB8295—87bzxZ.net
This standard was drafted by the South China Tropical Crop Products Processing and Design Institute. The main drafter of this standard is Zhou Hongqing
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