Changes from adopted text to adopted text

Removedwhere: V = ml volume of the sample used.

RemovedExpress the results as sodium dodecylbenzene sulphonate (MW 348).

Removed2.6. Expression of results

RemovedExpress the results as MBAS mg/l to the nearest 0,1.

Removed3. Determination of non-ionic surfactants in biodegradation test liquors

Removed3.1. Principle

RemovedSurface active agents are concentrated and isolated by gas stripping. In the sample used, the quantity of non-ionic surfactant should be in the range 250-800 g.

RemovedThe stripped surfactant is dissolved in ethyl acetate.

RemovedAfter phase separation and evaporation of the solvent, the non-ionic surfactant is precipitated in aqueous solution with modified Dragendorff reagent (KBiI4 + BaCl2 + glacial acetic acid).

RemovedThe precipitate is filtered, washed with glacial acetic acid and dissolved in ammonium tartrate solution. The bismuth in the solution is titrated potentiometrically with pyrrolidinedithiocarbamate solution at pH 4-5 using a bright platinum indicator electrode and a calomel or silver/silver chloride reference electrode. The method is applicable to non-ionic surfactants containing 6-30 alkylene oxide groups.

RemovedThe titration result is multiplied by the empirical factor of 54 for conversion to the reference substance nonylphenol condensed with 10 mols ethylene oxide (NP 10).

Removed3.2. Reagents and Equipment

RemovedReagents are to be made up in deionised water.

Removed3.2.1. Pure ethyl acetate, freshly distilled.

Removed3.2.2. Sodium bicarbonate, NaHCO3 AR.

Removed3.2.3. Dilute hydrochloric acid [20 ml concentrated acid (HCl) diluted to 1000 ml with water]

Removed3.2.4. Methanol AR, freshly distilled, stored in a glass bottle.

Removed3.2.5. Bromocresol purple, 0,1 g in 100 ml methanol.

Removed3.2.6. Precipitating agent: the precipitating agent is a mixture of two volumes of solution A and one volume of solution B. The mixture is stored in a brown bottle and can be used for up to one week after mixing.

Removed3.2.6.1. Solution A

RemovedDissolve 1,7 g bismuth nitrate, BiONO3.H2O AR, in 20 ml glacial acetic acid, and make up to 100 ml with water. Then dissolve 65 g potassium iodide AR in 200 ml water. Mix these two solutions in a 1000 ml measuring flask, add 200 ml glacial acetic acid (point 3.2.7) and make up to 1000 ml with water.

Removed3.2.6.2. Solution B

RemovedDissolve 290 g barium chloride, BaCl2.2H2O AR, in 1000 ml of water.

Removed3.2.7. Glacial acetic acid 99-100 % (lower concentrations are unsuitable).

Removed3.2.8. Ammonium tartrate solution: mix 12,4 g tartaric acid AR and 12,4 ml of ammonia solution AR (d = 0,910 g/ml) and make up to 1000 ml with water (or use the equivalent amount of ammonium tartrate AR).

Removed3.2.9. Dilute ammonia solution: 40 ml ammonia solution AR (d = 0,910 g/ml) diluted to 1000 ml with water.

Removed3.2.10. Standard acetate buffer: dissolve 40 g solid sodium hydroxide AR, in 500 ml water in a beaker and allow to cool. Add 120 ml glacial acetic acid (point 3.2.7). Mix thoroughly, cool and transfer to a 1000 ml volumetric flask. Make up to the mark with water.

Removed3.2.11. Pyrrolidinedithiocarbamate solution (known as ‘carbate solution’): dissolve 103 mg sodium pyrrolidinedithiocarbamate, C5H8NNaS2.2H2O, in about 500 ml water, add 10 ml of n-amyl alcohol AR and 0,5 g NaHCO3 AR, and make up to 1000 ml with water.

Removed3.2.12. Copper sulphate solution (for standardisation of point 3.2.11).

RemovedSTOCK SOLUTION

RemovedMix 1,249 g copper sulphate, CuSO4.5H2O AR, with 50 ml 0,5 M sulphuric acid and make up to 1000 ml with water.

RemovedSTANDARD SOLUTION

RemovedMix 50 ml stock solution with 10 ml 0,5 M H2SO4 and make up to 1000 ml with water.

Removed3.2.13. Sodium chloride AR.

Removed3.2.14. Gas-stripping apparatus (see Figure 5). The diameter of the sintered disc must be the same as the internal diameter of the cylinder.

Removed3.2.15. Separating funnel, 250 ml.

Removed3.2.16. Magnetic stirrer with magnet 25-30 mm.

Removed3.2.17. Gooch crucible, diameter of the perforated base = 25 mm, Type G4.

Removed3.2.18. Circular glass-fibre filter papers, 27 mm diameter with fibre diameter 0,3-1,5 m.

Removed3.2.19. Two filter flasks with adapters and rubber collars, 500 and 250 ml respectively.

Removed3.2.20. Recording potentiometer fitted with a bright platinum indicator electrode and a calomel or silver/silver chloride reference electrode with a 250 mV range, with automatic burette of 20-25 ml capacity, or alternative manual equipment.

Removed3.3. Method

Removed3.3.1. Concentration and separation of the surfactant

RemovedFilter the aqueous sample through a qualitative filter paper. Discard the first 100 ml of the filtrate.

RemovedInto the stripping apparatus, previously rinsed with ethyl acetate, place a measured quantity of the sample, such that it contains between 250-800 g non-ionic surfactant.

RemovedTo improve the separation add 100 g sodium chloride and 5 g sodium bicarbonate.

RemovedIf the volume of the sample exceeds 500 ml, add these salts to the stripping apparatus in solid form, and dissolve by passing nitrogen or air through.

RemovedIf a smaller-sized sample is used, dissolve the salts in 400 ml water and then add to the stripping apparatus.

RemovedAdd water to bring the level to the upper stopcock.

RemovedCautiously add 100 ml ethyl acetate on top of the water.

RemovedFill the wash-bottle in the gas-line (nitrogen or air) two-thirds full with ethyl acetate.

RemovedPass a gas stream of 30-60 l/h through the apparatus; the use of a flowmeter is recommended. The rate of aeration must be increased gradually at the beginning. The gas rate must be so adjusted that the phases remain noticeably separate to minimise the mixing of the phases and the solution of the ethyl acetate in the water. Stop the gas flow after five minutes.

RemovedIf there is a reduction of more than 20 % in the volume of the organic phase through solution in water, the sublation must be repeated paying special attention to the rate of gas flow.

RemovedRun off the organic phase into a separating funnel. Return any water in the separating funnel from the aqueous phase — it should only be a few ml — to the stripping apparatus. Filter the ethyl acetate phase through a dry qualitative filter paper into a 250 ml beaker.

RemovedPut a further 100 ml ethyl acetate into the stripping apparatus and again pass nitrogen or air through for five minutes. Draw off the organic phase into the separating funnel used for the first separation, reject the aqueous phase and run the organic phase through the same filter as the first ethyl acetate portion. Rinse both the separating funnel and the filter with about 20 ml ethyl acetate.

RemovedEvaporate the ethyl acetate extract to dryness using a water-bath (fume cupboard). Direct a gentle stream of air over the surface of the solution to accelerate the evaporation.

Removed3.3.2. Precipitation and filtration

RemovedDissolve the dry residue from 3.3.1 in 5 ml methanol, add 40 ml water and 0,5 ml dilute HCl (point 3.2.3) and stir the mixture with a magnetic stirrer.

RemovedTo this solution add 30 ml of precipitating agent (point 3.2.6) from a measuring cylinder. The precipitate forms after repeated stirring. After stirring for ten minutes leave the mixture to stand for at least five minutes.

RemovedFilter the mixture through a Gooch crucible, the base of which is covered with a glass-fibre filter paper. First wash the filter under suction with about 2 ml glacial acetic acid. Then thoroughly wash the beaker, magnet, and crucible with glacial acetic acid, of which about 40-50 ml is necessary. It is not necessary to quantitatively transfer the precipitate adhering to the sides of the beaker, to the filter, because the solution of the precipitate for the titration is returned to the precipitating beaker, and the remaining precipitate will then be dissolved.