BS ISO 788:2021 pdf download – Ultramarine pigments
7.2Reagents and materials
Use only reagents of recognized analytical grade and water of at least grade 3 as specified in ISO 3696.
7.2.1Sodium sulfite, anhydrous,CAS-No 7757-83-7.
7.2.2 Formaldehyde solution. Dissolve 8 ml formaldehyde solution [37,0 % to40,0 %(mass fraction).CAS-No 50-00-0] and dilute to 100 ml.
7.2.3 Acetic acid solution, 30 % (volume fraction). Dissolve 30 ml acetic acid [99,5 %(mass fraction).p=1,42 g/ml , CAS-No 64-19-7] in water and dilute to 100 ml.
7.2.4 lodine solution. Weigh 0,13 g iodine (CAS-No 7553-56-2) and 0,35 g potassium iodide (CAs-No7681-11-0) and dissolve in 100 ml water, transfer into a brown bottle and dilute to 1 000 ml.
7.2.5Sodium thiosulfate standard titration solution, c (NazS203)= 0,1 mol/1.
7.2.6Soluble starch solution,5 g/l.
7.2.7 Sodium thiosulfate standard titration solution, c(NagS203)=0,002 mol/l.Dilute the sodiumthiosulfate standard titration solution (7.2.5) with water.
Use ordinary laboratory apparatus and burettes, pipettes and one-mark volumetric flasks in accordancewith the requirements of ISO 385, ISO 648 and ISO 1042, respectively, together with the following.
7.3.1 Conical flask, 250 ml with a narrow neck and equipped with a ground-glass stopper.7.3.2Volumetric flask, 250 ml.
7.3.3Pipette, 20 ml, 25 ml, 50 ml.7.3.4Electric heating board.
7.3.5 Burette, 50 ml, graduated in 0,1 ml divisions.7.3.6 Balance, with an accuracy of o,1 mg.
7.4 Procedure
7.4.1 Preparation and determination of the test solutionCarry out the determination in duplicate.
Weigh about 7 g to 10 g (to the nearest 0,1 mg) of the sample into a 250 ml conical flask (7.3.1) and add 5 g of anhydrous sodium sulfite (7.2.1) and 70 ml water. Boil under reflux for about 15 min, then cool down to room temperature and transfer the mixture into a 250 ml volumetric flask (7.3.2). Dilute the solution to scale with water and mix well. Store the mixture for about 60 min or separate it using a centrifuge. Remove 25 ml of the supernatant fluid using a single-line pipette and pour it into a 250 ml conical flask.
This is the test solution. Add 50 ml formaldehyde solution (7.2.2) to the test solution, shake it for 5 min. Add 5 ml acetic acid solution (7.2.3), stir the mixture evenly and add a known volume of iodine solution (7.2.4) (usually 50 ml) to ensure the presence of excessive iodine. Gently shake the solution mix it completely, add soluble starch solution (7.2.6) and titrate the excess iodine with sodium thiosulfate standard titration solution (7.2.7). Record the volume of sodium thiosulfate standard titration solution as V 1 .
7.4.2 Determination of a blank test solution Except for adding samples, carry out a blank test exactly the same way as the sample test, using the same amount of reagent, by identical analysis procedures. Record the volume of sodium thiosulfate standard titration solution as V 2
7.5 Calculation and expression of results
Calculate the free sulfur content ω, as mass fraction in per cent, according to Formula (1):
V 2 is the volume, in millilitres, of sodium thiosulfate standard titration solution in the blank test;
V 1 is the volume, in millilitres, of sodium thiosulfate standard titration solution, which is consumed by the titration sample;
c is the exact value of the concentration, in moles per litre, of sodium thiosulfate standard titration solution;
m is the numerical value of the sample mass, in grams;
0,032 0 is the mass of sulfur equivalent to 1,00 ml iodine solution c(1/2 I 2 ) = 1 000 mol/l.
8 Determination of the elements content
8.1 Reagents and materials
8.2.1 Analytical instrument with an appropriate detection limit, for example, atomic absorptionspectroscopy(AAS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), etc.
8.2.2 Balance, with the accuracy of 0,1 mg.
8.2.3 Microwave digestion instrument, can be closed digestion, with temperature control device.
8.2.4Volumetric flask, hydrofluoric acid resistant, 50 ml, 100 ml.
8.2.5 Filter membrane, with the aperture size of 0,45 um.
8.2.6 Nitric acid solution, water and nitric acid (8.1.1) with a volume ratio of 1 to 1.
All glass containers should be soaked in nitric acid solution (8.2.6) for 24 h, then washed with waterand dried before using.
8.3 Procedure
8.3.1 Preparation and determination of the test solution
Weigh about 0,1 g to 0,2 g (to the nearest 0,1 mg) of the sample into a microwave digestion tank andadd 9 ml nitric acid (8.1.1), 1 ml hydrofluoric acid (8.1.2) dropwise, respectively. When no bubbles areproduced in the solution, close the digestion tank and place it into the microwave digestion instrument(8.2.3). Set the appropriate digestion conditions. After the microwave digestion is completed, cooldown the digestion tank to room temperature and then open it. Wash the inner wall and inner coverof the digestion tank with a small amount of water.Quantitatively transfer the digestion solution intoa one-mark volumetric flask(8.2.4).Make up to the mark with water, stopper it and mix well.Filter thesolution with a filter membrane(8.2.5).Test the solution within 24 h.
Select the analytical instrument with an appropriate detection limit to determine the content ofelements in the test solution and the reagent blank solution.
Refer to the instrument’s operation manual before the determination, and include the information ofanalytical instruments in the test report.