BS ISO 17322:2015 pdf download – Fertilizers and soil conditioners — Analytical methods for Sulfur Coated Urea (SCU)
7Determination of the mass fraction of sulfur7.1 Principle
Use water and sulfur-saturatedacetone solution to extract water-soluble and acetone-soluble substances,accordingto the sulfur’s behaviour of solubility.Then, extract all the sulfur by carbon disulfide.Calculatethe content of sulfur by the subtraction method.
7.2.3 Carbon disulfide.
7.2.4Sulfur-saturated acetone solution.
Add a certain amount of sulfur into acetone, and stir continuously. Some more sulfur should be addedin the acetone as long as the former can be dissolved thoroughly,until sulfur precipitate from acetone.
7.3.1Ordinary laboratory apparatus.
7.3.2 Balance, capable of weighing to the nearest 0,000 1g
7.3.3 Glass crucible filter, No. 4, volume of 30 ml.
7.3.4Drying oven, capable of being controlled at (100 ± 2) ℃.7.4Procedure
7.4.1Determination of the sulfur content
Warning —This method of analysis involves the use of carbon disulfide (CS2). Special safetymeasures shall therefore be taken, in particular with regard to the following:
the storage of CSz;
protective equipment for staff;occupational hygiene;
prevention of fire and explosions;-disposal of the reagent.
Warning —This method requires a highly skilled staff and a suitable equipped laboratory.The replication experiments shall be done for the determination.
Weigh a certain amount of (with 200 mg to 300 mg sulfur contained) as-prepared test sample (crushed)into a 125 ml Erlenmeyer flask with a plug.Add 50 ml of water into the flask precisely before the flasksealed with the plug.Shake the flask vigorously to dissolve the urea content thoroughly.Remove all contents from the triangular flask into a glass crucible filter(7.3.2) which has been dried to a constantweight at (100 ± 2) °C, and then wash the flask five to six times with water.
Wash the glass crucible filter and its contents with 10 ml sulfur-saturated acetone solution(7.2.4), thecontent should be dried up by a vacuum pump, repeat this operation four times. Then, dehydrate thesample in the drying oven at (100 ± 2) C for i h; after drying, remove the sample from the dryer andcool it down to room temperature and weigh.
Pipette another 10 ml carbon disulfide to wash the test portion, then the content should be dried up bya vacuum pump, repeat this operation 3 to 5 times,until all the sulfur content within the test portionhas been rinsed out.
Then, dehydrate the test portion in the drying oven at (100 ± 2) °C for 1 h; after drying, remove thesample from the dryer and cool it down to room temperature and weigh.
The mass difference between the above two weights should be the mass of sulfur content.
Replace the test portion with other inert material free of sulfur (ordinary urea, for example), and carryout the blank test in parallel with the determination using the same procedure and the same quantitiesof all reagents.
Calculate the sulfur content (represented by the fraction ofSelement),wa,expressed in the mass fraction(%), according to Formula (7):
m 6 is the mass of the test portion, in the unit of gram (g);
m 7 is the mass of the test portion after washing by sulfur-saturated acetone, in the unit of gram (g);
m 8 is the mass of the test portion after washing by carbon disulfide, in the unit of gram (g);
m 9 is the mass of sulfur in the blank test, in the unit of gram (g).
Express the result to within two decimal places. The average value of the results of parallel experiments shall be defined as the result of the test.
8 Determination of the mass fraction of biuret
Under alkaline conditions in the presence of potassium sodium tartrate, biuret forms a purple complex with copper salts. The absorbance of the solution is measured at a wavelength of 550 nm.
8.2.1 Alkaline solution of potassium sodium tartrate.
In a 1 L volumetric flask, dissolve 40 g of sodium hydroxide in 500 ml water and leave it to cool. Add 50 g of potassium sodium tartrate (NaKC 4 H 4 O 6 4H 2 O). Make the flask up to the mark with water and leave to stand for 24 h before use.