BS/EN 17042-2018 pdf download.Fertiliizers-Determination of boron in concentrations 10 using acidimetric titration.
62 Methyl red indicator solution.
Dissolve 0,1 gof methyl red (C15H1SN3OZ) in 50 ml of ethanol (95%) in a 100 ml volumetric flask (7). Make up the volume to 100 ml with water (6..1). Mix thoroughly.
6.3 Diluted hydrochloric acid solution, with a concentration of about c 0,5 mol/l.
Mix 1 volume of hydrochloric acid llCl (p = 1,18 g/ml) with 20 volumes of water (j).
6.4 Sodium hydroxide solution, with a concentration of about c = 0,5 mol/l.
The solution shall be free from carbon dioxide. Dissolve 20 gof sodium hydroxide (NaOH) in pellet form in a 1 000 ml volumetric flask (2.6) containing about 800 ml of boiled water (Jj. After dissolution and cooling make up to 1 000 ml with boiled water (6.1) and mix thoroughly.
6.5 Standard sodium hydroxide solution, with a concentration of about c = 0,025 rnol/L
The solution shall be free from carbon dioxide. Dilute 0,5 mol/l sodium hydroxide solution () 20 times with boiled water and mix thoroughly. The value of the solution expressed as boron (B) is to be determined ().
6.6 Boron calibration solution, p = 100 mg/I.
Weigh to the nearest 0,1 mg 0,571 9 g of boric acid (H3B03), dissolve in water (J), transfer quantitatively into a 1 000 ml volumetric flask (2.6). make up to volume with water (.1) and mix thoroughly. Transfer to a plastic bottle for storage in a refrigerator at 4 °C to 8 °C.
Commercially available stock solution with adequate specification may be used. The solution is generally considered to he stable for one year, hut in reference to guaranteed stability, the recommendations of the manufacturer shall be considered.
6.7 D-mannitol, (C6H 1406) powder.
6$ Sodium chloride (NaCl),
7 Apparatus
7.1 pH meter, with glass electrode.
72 Magnetic stirrer.
8 Procedure
8.1 Test solution
Place an aliquot (a) of the extract containing 2 mg to 4 mg boron into a 400 ml beaker (7±). Add 150 ml of water (Jj. Add several drops of the methyl red indicator solution (2). If necessary acidify by adding hydrochloric acid solution () up to the point of change of the indicator. Then add 3 g of sodium chloride (), bring to boiling to drive off the carbon dioxide. Allow to cool.
Place the beaker on the magnetic stirrer (22) and mix by using a PTFE rod (Z4). Insert the precalibrated p11 meter electrodes (7.1) into the beaker and adjust the p11 first approximately up to 5 with the 0,5 mol/l sodium hydroxide solution (4), then to exactly pH = 6,3 with the 0,025 mol/l sodium hydroxide solution (). Add 20 g of D-mannitot (Z). dissolve completely and titrate with the 0,025 mol/l sodium hydroxide solution () to pH 6,3 (at least 1 mm stability). Let Xi be the volume of
0.025 mol/l sodium hydroxide solution () required.
82 Blank solution
Prepare a blank solution by repeating the whole procedure from the preparation of solution stage. omitting only the fertiliser. LetXo be the volume of 0,025 mol/l sodium hydroxide solution () required.
8.3 Boron (B) value of the sodium hydroxide solution ()
Pipette 20 ml of the calibration solution (), into a 400 ml beaker (7.3) and add several drops of methyl red indicator solution (2). The beaker contains 2,0 mg of boron. Add 3 g of sodium chloride () and the hydrochloric acid solution () up to the point of change of the indicator solution (62). Make up the volume with water (.1) to about 150 ml and bring gradually to the boil so as to eliminate carbon dioxide. Allow to cool.
Place the beaker (Z) on the magnetic stirrer (22) and mix by using a PTFE rod (Z14). Insert the precalibrated pH meter electrodes (71) into the beaker and adjust the pH first approximately up to 5 with the 0,5 mol/l sodium hydroxide solution (4J, then to exactly pH = 6,3 with the 0,025 mol/l sodium hydroxide solution ().
Add 20 g of D-mannitol (Z), dissolve completely and titrate with the 0,025 mol/I sodium hydroxide solution (5) to p11 6,3 (at least 1 mm stability). Let V be the volume of 0,025 mol/I sodium hydroxide solution () required.
Prepare a blank solution in the same way, substituting 20 ml of water for the calibration solution. Let Vo be the volume required.
Calculate the boron value (F) in mg/mi of the standard NaOFl solution () according to Formula (1).BS/EN 17042-2018 pdf download.