EN 903-1993 pdf download.Water quality — Determination of anionic surfactants by measurement of the methylene blue index MBAS.
4.8 Neutral met hylene blue, solution.
NOTE The solid mcthylc’ne blue used should be the purest avail able.
Dissolve 0,350 g methylene blue in water and dilute to 1 000 ml.
Prepare the solution at least 24 h before use. This solution is stable for at least 2 weeks.
The absorbance of the chloroform phase of the blank tent (see 7.2) measured against chloroform shall not exceed 0,02 per 10 mm layer thickness at 650 nm. In the case of higher blank absorbances. use other batches of methylene blue andlor purify the mnethylene blue solution by extraction as follows.
Place the methylene blue solution in a suitably large separating funnel. For each 100 ml 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 methylene blue solution. Repeat the extraction and rinse as before. Discard the chloroform extracts; collect for reuse after treatment.
4.9 Acid rnethvlene blue, solution.
Dissolve 0,350 g methylene blue in 500 ml of water and add 6.50 ml of sulfuric acid, p = 1,84 gIml. 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 layer thickness at 650 nm. In the case of higher blank absorbances, either wash twice the methylene blue solution with chloroform for purification (see 4.8) or use other
batches of methylene blue.
4.10 Buffer solution, pH 10.
4.10.1 Dissolve 24 g sodium hydrogen carbonate
(NaHC’O) and 27 g anhydrous sodium carbonate
(Na2CO3) in water and dilute to 1 000 ml with
water.
4.10.2 Alternatively, especially for water with high hardness, the following buffer solution may be used.
4.10.2.1 Disodiurn telraborczte
(NaB1O7. 10H20), 0,05 molIl, solution.
Dissolve 19 g disodium tetraborate decahydrate in 1 000 ml of water.
This solution is stable for at least 2 weeks if stored in a glass stoppe red bottle.
4.10.2.2 Sodium hydroxide (NaOH), 0,1 mol/1.
Dissolve 4 g sodium hydroxide pellets in 1 litre of water.
This solution is stable for at least 2 weeks if stored in a polyethylene stoppered glass bottle.
4.10.2.3 Alkaline borate solution Mix equal volumes of sodium tetraborate solution (4.10.2.1) and sodium hydroxide solution (4.10.2.2).
This solution is stable for at least 1 week if stored in a polyethylene stoppered glass bottle.
4.11 Dodecyl benzene sulfonic acid methyl ester (tetra-propylene type) (C19H3203S), stock standard solution.
Weigh, preferably from a weighing pipette. 400 mg to 450 mg of dodecyl benzene sulfonic acid methyl ester to the nearest 0,1 ing into a round bottom flask, add 50 tnl of ethanolic sodium hydroxide solution (4.7) and some anti-bumping granules. Attach the reflux condenser and boil for 1 h. After cooling, rinse the condenser and the ground glass joint with about 30 ml of ethanol (4.4) and add the rinsings to the contents of the flask. Neutralize the solution with sulfuric acid (4.6) against J)henolphthalein (4.12) until it becomes colourless. Transfer the solution to a 1 000 ml one-mark volumetric flask, dilute to the mark with water and mix.
This standard solution is stable for at least 6 months.
NOTE Although the dodecvl bcnzenc sulfonic acid methyl ester is preferable as it is a guaranteed non.hvgroscopic standard, the calibration graph (see 7.3) may alternatively be established with the aid of the commercially available sodium salt of dodecane.1 sulfonic acid (l1..,NuOS). dodccane.I sulfuric acid (C1H3NaO4S) or dioctyl sulfosuccinic acid (CH37NuOS).
4.12 Phenolphthalein, indicator solution. Dissolve 1,0 g phenolphthalein in 50 ml of ethanol (4.4) and add, while stirring continuously, 50 ml of water. Filter off any precipitate that forms.
5 Apparatus
Ordinary laboratory equipment, and
5.1 pH-meter, with suitable electrodes made from glass.
5.2 Spectrometer, with selectors for discontinuous variation, capable of measurement at 650 nm, equipped cells of optical path length with 10 to 50 mm cells.
5.3 Gas-stripping apparatus (see the Figure; the apparatus is corn rnerdally available).
The diameter of the sintered disc shall be the same as the internal diameter of the cylinder.
NOTE To make cleaning easier, the apparatus should preferably be equipped with a spherical connection under the stripping funnel. The fixing member should also be divisible.EN 903-1993 pdf download.