60 RECOMMENDED METHODS FOR THE ANALYSIS OF TRADE EFFLUENTS [Vol. 83 Recommended Methods for the Analysis of Trade Effluents PREPARED BY THE JOINT A.E;.C.M. - S.A.C. COMMITTEE ON METHODS FOR THE ANALYSIS OF TRADE EFFLUENTS Methods for the Determhation of Phosphorus and Acid-soluble Sulphate PhosphLorus PRINCIPLE OF METHOD- Phosphorus may be present in effluents as phosphate (ortho-, meta-, pyro- or polyphosphate) and in organic combination. The phosphorus is first converted to orthophosphate, if not already present as such. This is then determined colorimetrically (by using Tschopps’s reagent) as the molybdenum blue complex formed by the reduction of molybdophosphoric acid. RANGE- For phosphorus contents of (a) up to 7Ei pg (instrumental method) ; or (b) up to 25 pg (visual colour-comparison method).APPLICABILITY- The method is of wide application. Ferric iron in concentrations several times that of the phosphorus does not interfere. The conditions of test may be modified1 to differentiate between total inorganic phosphate and total phosphorus present in the effluent. NOTE-It is possible that extraction procedures1S2 may be of assistance in eliminating inter- ferences. In these procedures the molybdophosphoric acid is extracted by a solvent such as n-butanol, and the reduction is subsequently carried out in this medium. REAGENTS- Ammonium mollybdate solution-Dissolve 10 g of ammonium molybdate, (NH,),Mo,O,~.~H,O, in 100ml of distilled water. Add this solution slowly, and with stirring, to 300 ml of diluted sulphuric acid (1 + 1).Store in a borosilicate- glass bottle in the dark. Standard phosphate solution A-Dissolve 0.439 g of potassium dihydrogen orthophosphate in distilled water, add 5 ml of diluted sulphuric acid (1 + 1) and dilute the solution to 1 litre. Standard phosphate solution B-Dilute 10.0 ml of solution A to 1 litre with distilled water. Prepare this solution freshly each day. 1 ml = 1 pg of phosphorus. Metol - sdphite solution (Tscho$es’s rmgent)-Dissolve 40 g of sodium met a- bisulphite and 1 g of sodium sulphite, Na2S0,.7H,O, in cold distilled water, add 0-2 g of Metol (p-methylaminophenol sulphat e) and stir well until solution is complete. Dilute to 100ml with distilled water and mix. PROCEDURE- (a) Total inorganic phosphate- Select a suitable volume of the efiluent sample (not exceeding 10 ml) to contain up to 75 pg of phosphorus if the determination is to be made instrumentally, or up to 25 pug if visual colour comparison is to be made.Add sufficient sulphuric acid to make the acidity 5 N and boil the solution for 16 minutes, to convert any condensed phosphates to orthophosphate, keeping the volume constant. Cool, filter, if necessary, and almost neutralise to phenolphthalein with sodium hydroxide so1,ution.January, 19581 RECOMMENDED METHODS FOR THE ANALYSIS OF TRADE EFFLUENTS 61 Add 5 ml of ammonium molybdate solution and 5 ml of Metol- sulphite solution. Heat the solution in a boiling-water bath for 30 minutes and then cool to room temperature. Transfer the solution to a 50-ml calibrated flask and dilute to the mark with distilled water. Proceed to determine the phosphorus content colorimetrically, either by the instrumental method or by visual colour comparison.Instrumental method-Measure the optical densities of the test and blank solutions in a spectrophotometer or in an absorptiometer, using 4-cm or 1-cm cells according to the depth of colour, and using a wavelength of 6 5 0 0 ~ in a spectrophotometer or a suitable red filter in an absorptiometer. Use distilled water in the comparison cell. Read the number of micrograms of phosphorus equivalent to the observed optical densities of the test and blank solutions from a previously prepared calibration graph, and so obtain the net measure of inorganic phosphate (as phosphorus) in the sample. Carry out a blank determination on all reagents used.Prepare the calibration graph as follows- Measure appropriate amounts of standard phosphate solution B into a series of conical flasks: for the 4-cm cell the standards should cover the range 0 to 1Opg and for the l-cm cell they should cover the range 10 to 75pg of phosphorus. To the contents of each flask add 5 ml of ammonium molybdate solution and 5 ml of Metol- sulphite solution and proceed as for the test sample. Measure the optical densities and construct a graph relating the optical densities to the number of micrograms of phosphorus. Visual colour-comparison method-Prepare a series of standards as for the instrumental method, covering the range 0 to 25 pg of phosphorus. Compare the colours visually in Nessler cylinders. Alternatively, proprietary coloured discs may be used in a comparator instead of solution standards, and the makers’ instructions should be followed.It should be noted that some proprietary coloured discs are calibrated in terms of P,O,; the conversion factor to phosphorus is 0.437. Whichever method of determination is used (instrumental or visual comparison), express the total inorganic phosphate content as milligrams of phosphorus per litre of sample. (b) Total phosphoms- Digest 5 to 10 ml of the effluent sample, over a micro-burner, with 0.3 to 0.5 ml of sulphuric acid, sp.gr. 1.84, in a micro-Kjeldahl flask or boiling-tube. Continue the digestion until the solution is colourless, avoiding loss by fuming. Cool and transfer the solution to a 50-ml calibrated flask, rinsing the digestion vessel with sufficient distilled water to bring the volume to about 20ml; filter if necessary.Almost neutralise the solution to phenolphthalein with sodium hydroxide solution. Finally, dilute the solution to the mark with distilled water. Measure a suitable aliquot of this solution and proceed as described under “Total Inorganic Phosphate,” commencing at “Add 5 ml of ammonium molybdate solution . . . ” in (a) above. Carry out a blank determination on all reagents used. Express the total phosphorus content as milligrams of phosphorus per litre of sample. REFERENCES 1. 2. Pons, W. A., and Guthrie, J. D., I n d . Eng. Chem., Anal. Ed., 1946, 18, 184. Martin, J. B., and Doty, D. M., Anal. Chem., 1949, 21, 965. Acid-soluble Sulphate PRINCIPLE OF METHOD- conditions1 and determined gravimetrically.The acid-soluble sulphates are precipitated as barium sulphate under controlled52 RECOMMENDED METHODS FOR THE ANALYSIS OF TRADE EFFLUEXTS RANGE- For sulphate contents between 8 anti 60mg, expressed as SO,". [Vol. 83 APPLICABILITY- If it is desired to include the sulphate ion of insoluble compounds, such as barium sulphate, an appropriate aliquot of the well-mixed sample must be neutralised, made slightly acid with hydrochloric acid, evaporated to dryness, ignited and the utjual methods of quantitative gravimetric analysis applied to the residue. REAGENTS- The method is generally applicable. Hydrochloric acid, sp.gr. 1.18. HydrochZoric acid, diluted (1 + 1). Hydrochloric acid, dilztte, approximately 0.5 N. Ammonium hydroxide, diluted (1 + 3)--Dilute 1 volume of ammonium hydroxide, Barium chloride solution, 10 per cent.w / v . Methyl orange indicator solution-A 0.04 per cent. w/v solution in 20 per cent. sp.gr. 0.880, with 3 volumes of distilled water. ethanol. PROCEDURE- Measure an aliquot of the effluent sample which is expected to contain between 8 and 60 mg of acid-soluble sulphate. Neutralise with 0.5 N hydrochloric acid, using methyl orange indicator solution; then add 1 ml of hydrochloric acid, sp.gr. 1.18, and boil the mixture. Adjust the volume to about 150ml by concentration or dilution with distilled water. Filter the solution and wash the residue on the filter-paper until the washings are free firom chloride. Neutralise the combined filtrate and washings with diluted ammonium hydroxide (1 + 3), adding more indicator solution if necessary.Adjust the volume to about 200 ml with distilled water, add 2 ml of diluted hydrochloric acid (1 + I) and heat to boiling. Boil the solution for ab0u.t 30 seconds, remove it from the hot-plate and add 10 ml of barium chloride solution (or 15 ml if less than 20 mg of sulphate are present) from a fast-flowing pipette to the centre of the solution, with thorough mixing. Allow the mixture to stand for '20 minutes; then filter off the precipitate on an ashless filter-paper pulp pad, using gravity filtration and washing with hot distilled water until the washings are free from chloride. Transfer the wet pad and precipitate to a previously ignited and weighedsilica capsule, wiping off with a piece of moist filter-paper any precipitate adhering to the funnel, insert the capsule on a 6-mm silica plate directly into a well-ventilated muffle furnace at 800" C, ignite, cool anti weigh the barium sulphate. Weight of BaSO, (in mg) x 0.41 16 = mg of sulphate (as SO,"). Express the result as milligrams of acid-soluble sulphate (as SO,") per litre of sample. REFERENCE 1. Mott, R. A., Ruell, D. A., and Wilkinson, H. C . , Fuel, 1955, 34, 78 and 87.