ISO 7875-1 pdf download – Water quality – Determination of surfactantsPart 1: Determination of anionic surfactants by measurement of the methylene blue index (MBAS).
The absorbence of the chloroform phase of the blank test (see 7.2), measured against chloroform, shall not exceed 0.2 per 10 mm of optical path length at 650 nm In the case of higher absorbances during the blank test, use other batches of methylene blue anWor purify the methylene blue solution by extraction as follows.
Place the methylene blue solution in a suitably large separating funnel. For each 100 ml of methylene blue solution, add 200 ml of buffer solution (4.10) and 200 ml of chloroform (4,3), Shake for 30 s and allow to separate Run off the chloroform layer as completely as possible and rinse the aqueous layer without shaking with 60 ml of chloroform for each 100 ml of methylene blue solution. Repeat the extraction and rinse as before. Discard the chloroform extracts; collect for reuse after treatment.
4.9 Methylene blue, acidic solution.
Dissolve 0.350 g of methylene blue in 500 ml of water and add 650 ml of sulfuric acid (p 1.84 g/ml). Dilute with water to 1 000 ml after mixing.
Prepare the solution at least 24 h before use.
The absorbance of the chloroform phase of the blank test (see 7.2, measured against chloroform, shall not exceed 0,02 per 10 mm of optical path length at 650 nm. In the case of higher blank absorbarices. either wash the methylene blue solubon twice with chloroform for purification (see 4.8) or use other batches of methylene blue.
4.10 Buffer solution, of pH 10.
4.10.1 Dissolve 24 g of sodium hydrogencarbonate (NaCO3), and 27 g of anhydrous sodium carbonate (Na2CO3) in water and dilute to 1 000 ml.
4.10.2 Alternatively, especially for very hard water, the buffer solution prepared in 4.10.2.3 may be used.
4.10.2.1 Disodium tetraborate (Na2B4O7 10H20), 0.05 maul solution.
Dissolve 199 of disodium tetraborate decahydrate in 1 000 ml of water.
This solution is stable f or at least 2 weeks if stored in a stoppered glass bottle.
4.10.2.2 Sodium hydroxide (NaQH), 0.1 mol/t solution.
Dissolve 4 g of sodium hydroxide pellets in 1 000 ml of water.
This solution is stable for at least 2 weeks if stored in a glass bottle with a polyethylene stopper.
Ii necessary, add water to bring the sample surface up to the level of the upper stopcock Isee figure 1). Add 100 ml of ethyl acetate (42) Fill the wash bottle in the gas line (nitrogen or air) two-thirds full with ethyl acetate. Pass a gas stream of 20 I/b to 50 I/h through the gas-stripping apparatus. Use of a flowmeter with variable area is recommended. Adjust the gas flow in such a way that the phases remain separate and no turbulence is produced at the interface. The significant mixing of the phases and consequent solution of ethyl acetate in the water is avoided. Stop the gas flow after 5 mm.
If a loss of more than 20 % (V/V) of the organic phase has occurred due to solution in the water phase, discard the test sample,
Run off the organic phase completely into a separating funnel. Return any water in the separating funnel (there should only be a few millilitres) to the gas-stripping apparatus.
Filter the ethyl acetate solution through a dry qualitative gas-f ilter paper into a 250 ml flask. Add a further 100 ml of ethyl acetate to the gas-stripping apparatus and again pass nitrogen or air through it for 5 mm, Separate the organic layer as described above, using the same separating funnel, filter, and add it to the first portion. Rinse the filter paper and funnel with 25 ml of ethyl acetate. Remove all the ethyl acetate solution on a water-bath under a hood. To speed up the process, direct a gentle air stream over the surface of the solution.
Dissolve the residue in about 5 ml of methanol (4.5) and 50 ml of water. Transfer the solution quantitatively to a 100 ml one-mark volumetric flask and dilute to the mark with water.
7.2 Blank test
With each series of test samples, carry Out a blank test in parallel with the determination, using the zero member of the set of calibration solutions (see 7.3).
Subtract the interpolated absorbance, A0. from the absorbence. A1 of the test sample. Under the given conditions the absorbance, A0. of the blank test shall not exceed 0,02 per 10 mm optical path length, otherwise the equipment and the reagent shall be checked carefully for any contamination.
ISO 7875-1 pdf download – Water quality – Determination of surfactantsPart 1: Determination of anionic surfactants by measurement of the methylene blue index (MBAS)
