{
  "url": "https://openlegislation.uk/fertilisers-sampling-and-analysis-amendment-regulations-1991/schedule-3",
  "json_url": "https://openlegislation.uk/fertilisers-sampling-and-analysis-amendment-regulations-1991/schedule-3.json",
  "legislation": "uksi/1991/2824",
  "legislation_title": "The Fertilisers (Sampling and Analysis) (Amendment) Regulations 1991",
  "legislation_url": "https://openlegislation.uk/fertilisers-sampling-and-analysis-amendment-regulations-1991",
  "path": "schedule/3",
  "kind": "schedule",
  "number": "3",
  "heading": "PROVISIONS TO BE ADDED TO PART I OF SCHEDULE 2 TO THE PRINCIPAL REGULATIONS",
  "text": "“17 EXTRACTION OF TOTAL CALCIUM, TOTAL MAGNESIUM, TOTAL SODIUM AND TOTAL SULPHUR IN THE FORM OF SULPHATES\nScope\n1 This method is for the extraction of total calcium, total magnesium, total sodium and total sulphur present in the form of sulphates.\nField of application\n2 This method applies to all fertilisers, for which a declaration of the total calcium, total magnesium, total sodium and total sulphur in the form of sulphates is required.\nPrinciple\n3 Dissolution by boiling in dilute hydrochloric acid.\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\nApparatus\n5 Electric hot plate with adjustable temperature.\nPreparation of the sample\n6 See method 1.\nProcedure\n7 7.1 Test sample.\nCalcium, magnesium, sodium and sulphur in the form of sulphates are extracted from a test sample of five grams weighed to within one milligram.\nHowever, when the fertiliser contains more than 15% of sulphur (S) i.e. 37.5% SO3, and more than 18.8% of calcium (Ca) i.e. 26.3% CaO, the extraction of calcium and sulphur is carried out on a test sample of one gram, weighed to within one milligram. Place the test sample in a 600 millilitre beaker.\n7.2 Preparation of the solution.\nAdd approximately 400 millilitres of water and, taking care when the sample contains a significant quantity of carbonates, 50 millilitres of dilute hydrochloric acid (4.1) a small amount at a time. Bring to the boil and maintain for 30 minutes. Allow to cool, stirring occasionally. Transfer quantitatively into a 500 millilitre graduated flask. Make up to volume with water, and mix. Pass through a dry filter into a dry container, discarding the initial portion. The extract must be completely clear. Stopper if the filtrate is not used immediately.\n18 EXTRACTION OF TOTAL SULPHUR\nScope\n1 This method is for the extraction of total sulphur contained in fertilisers in elemental form and/or in other chemical combinations.\nField of application\n2 This method applies to all fertilisers for which a declaration of the total sulphur present in various forms (elemental, thiosulphate, sulphite, sulphate) is required.\nPrinciple\n3 Elemental sulphur is converted in an alkaline medium into polysulphides and thiosulphate; these, together with any sulphites which may be present, are then oxidized with hydrogen peroxide. The various forms of sulphur are thus converted into sulphate which is determined by precipitation as barium sulphate (method 25).\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\n4.2 Sodium hydroxide solution, NaOH, 30% minimum (d = 1.33).\n4.3 Hydrogen peroxide solution, 30% w/w.\n4.4 Aqueous solution of barium chloride BaC122H20, 122 gram per litre.\nApparatus\n5 Electric hot plate with adjustable temperature.\nPreparation of the sample\n6 See method 1.\nProcedure\n7 7.1 Test sample.\nWeigh out to within one milligram a quantity of fertiliser containing between 80 and 350 milligrams of sulphur (S) or 200 and 875 milligrams SO3.\nAs a rule (Where S < 15%), weigh out 2.5 grams. Place the test sample in a 400 millilitre beaker.\n7.2 Oxidation.\nAdd 20 millilitres of sodium hydroxide solution (4.2) and 20 millilitres of water. Cover with a watch glass. Boil for five minutes on the hot plate (5). Remove from the hot plate. Using a jet of hot water, collect any material sticking to the sides of the beaker and boil for 20 minutes. Leave to cool.\nAdd 2 millilitre increments of hydrogen peroxide (4.3) until no reaction is observed. Six to eight millilitres of hydrogen peroxide will be necessary. Allow oxidation to continue for one hour, then bring to the boil for half an hour. Leave to cool.\n7.3 Preparation of the solution to be analysed.\nAdd approximately 50 millilitres of water and 50 millilitres of the hydrochloric acid solution (4.1).\nIf the level of sulphur (S) is less than 5%:\nfilter into a 600 millilitre beaker. Wash the residue on the filter several times with cold water. After washing, check for the absence of sulphate in the last drops of the filtrate using the barium chloride solution (4.4). The filtrate must be perfectly clear. Sulphate is determined on the whole of the filtrate in accordance with method 25.\nIf the level of sulphur (S) is at/above 5%:\ntransfer quantitatively into a 250 millilitre volumetric flask, make up to volume with water and mix. Filter through a dry filter into a dry container; the filtrate must be completely clear. Stopper if the solution is not to be used immediately. Determine sulphates on an aliquot of this solution by precipitation in the form of barium sulphate (method 25).\nEXTRACTION OF WATER-SOLUBLE CALCIUM, MAGNESIUM, SODIUM AND SULPHUR (IN THE FORM OF SULPHATES)\n19\nScope\n1 This method is for the extraction of water-soluble calcium, magnesium, sodium and sulphur (in the form of sulphates), so that the same extract can be used to determine each nutrient required.\nField of application\n2 This method applies solely to fertilisers for which a declaration of the water-soluble calcium, magnesium, sodium and sulphur (in the form of sulphates) is required.\nPrinciple\n3 The nutrients are dissolved in boiling water.\nReagents\n4 Distilled or demineralized water of equivalent quality.\nApparatus\n5 Electric hot plate with adjustable temperature.\nPreparation of the sample\n6 See method 1.\nProcedure\n7 7.1 Test sample.\n(a) Where fertilisers contain no sulphur or where they contain, at the same time, no more than 3% of sulphur (S) i.e. 7.5% SO3, and no more than 4% of calcium (Ca) i.e. 5.6% CaO, weigh out five grams of fertiliser to within one milligram.\n(b) Where fertilisers contain more than 3% of sulphur (S) and more than 4% of calcium (Ca), weigh out one gram of fertiliser to within one milligram.Place the test sample in a 600 millilitre beaker.\n7.2 Preparation of the solution.\nAdd approximately 400 millilitres of water and boil for 30 minutes. Allow to cool, stirring occasionally, and transfer quantitatively into a 500 millilitre graduated flask. Make up to volume with water and mix.\nFilter through a dry filter into a dry container: Discard the initial portion of the filtrate. The filtrate must be completely clear.\nStopper if the solution is not to be used immediately.\nEXTRACTION OF WATER-SOLUBLE SULPHUR\n20\nScope\n1 This method is for the extraction of water-soluble sulphur contained in fertilisers, in various forms.\nField of application\n2 This method applies to all fertilisers for which a declaration of the water-soluble sulphur trioxide is required.\nPrinciple\n3 Soluble forms of sulphur are dissolved in cold water and converted into sulphate by oxidation with hydrogen peroxide in an alkaline medium.\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\n4.2 Sodium hydroxide solution containing at least 30% NaOH (d = 1.33g/ml).\n4.3 Hydrogen peroxide solution, 30% w/w.\nApparatus\n5 5.1 500 millilitre graduated Stohmann flask.\n5.2 Rotary shaker, 30 to 40 turns per minute.\n5.3 Electric hot plate with adjustable temperature.\nPreparation of the sample\n6 See method 1.\nProcedure\n7 7.1 Test sample.\n(a) Where fertilisers contain a maximum of 3% of sulphur (S) i.e. 7.5% SO3, together with a maximum of 4% of calcium (Ca) i.e. 5.6% CaO, weigh out 5 grams of fertiliser to within one milligram.\n(b) Where fertilisers contain more than 3% of sulphur (S) together with more than 4% of calcium (Ca), weigh out one gram of fertiliser to within one milligram.\nPlace the test sample in a 500 millilitre flask (5.1).\n7.2 Preparation of the solution.\nAdd approximately 400 millilitres of water. Stopper. Shake (5.2) for 30 minutes. Make up to volume with water and mix. Pass through a dry filter into a dry container. Reject the first portion of the filtrate. Stopper if the solution is not to be used immediately.\n7.3 Oxidation of the aliquot portion to be analysed.\nTake an aliquot of the extraction solution not exceeding 50 millilitres and, if possible, containing between 20 and 100 milligrams of sulphur (S).\nMake up the volume to 50 millilitres with water, if necessary. Add three millilitres of sodium hydroxide solution (4.2) and two millilitres of hydrogen peroxide solution (4.3). Cover with a watch glass and boil gently for one hour on the hot plate (5.3). Keep adding one millilitre increments of hydrogen peroxide solution for as long as the reaction continues (maximum quantity five millilitres).\nThen leave to cool. Remove the watch glass and wash the underside into the beaker. Add approximately 20 millilitres of dilute hydrochloric acid (4.1). Make up to approximately 300 millilitres with water.\nDetermine the content of sulphates on the whole of the oxidised solution in accordance with method 25.\nEXTRACTION AND DETERMINATION OF ELEMENTAL SULPHUR\n21 WARNING\nThis method of analysis involves the use of carbon disulphide (CS2). Special safety measures must therefore be taken, in particular with regard to:\nthe storage of CS2,\nprotective equipment for staff,\noccupational hygiene,\nprevention of fires and explosions,\ndisposal of the reagent.\nThis method requires highly skilled staff and a suitably equipped laboratory.\nScope\n1 This method is for the extraction and determination of the elemental sulphur content of fertilisers.\nField of application\n2 This method applies to all fertilisers for which a declaration of the total sulphur in elemental form is required.\nPrinciple\n3 After the removal of soluble compounds, elemental sulphur is extracted by using carbon disulphide, followed by gravimetric determination of the sulphur extracted.\nReagents\n4 Carbon disulphide.\nApparatus\n5 5.1 100 millilitre extraction flask with ground glass stopper.\n5.2 Soxhlet apparatus, with the appropriate filter elements.\n5.3 Vacuum rotary evaporator.\n5.4 Electric oven, fan assisted, set at 90 ± 2°C.\n5.5 Petri dishes, five to seven centimetres in diameter, not exceeding five centimetres in height.\n5.6 Electric hot plate with adjustable temperature.\nPreparation of the sample\n6 See method 1.\nProcedure\n7 7.1 Test sample.\nWeigh out five to ten grams of the sample to an accuracy of one milligram and place in the thimble of the Soxhlet apparatus (5.2).\n7.2 Extraction of the sulphur.\nWash thoroughly the contents of the thimble with hot water to remove all soluble compounds. Dry in the oven at 90°C (5.4) for at least one hour. Place the thimble in the Soxhlet apparatus (5.2).\nPlace a few glass beads in the flask of the apparatus (5.1) and weigh (P0), then add 50 millilitres of carbon disulphide (4.1).\nConnect the apparatus, switch on and leave the elemental sulphur to be extracted for six hours. Switch off the heat and, after cooling, disconnect the flask. Connect the flask to the rotary evaporator (5.3) and evaporate until the contents of the flask have solidified in a spongy mass.\nExpression of results\n8 The percentage elemental sulphur (S) content of the fertiliser is as follows:\nImpure S (%) of the fertiliser=P1-P0m×100 Purity of sulphur extracted (%)=P2-P3n×100 Pure S (%) of the fertiliser=(P1-P0)(P2-P3)m×n×100 Where:\nm = the mass of the test sample of fertiliser in grams,\nP0 = the mass of the Soxhlet flask in grams,\nP1 = the mass of the Soxhlet flask and the impure sulphur after drying,\nn = the mass of the impure sulphur to be purified in grams,\nP2 = the mass of the Petri dish and the sample,\nP3 = the mass of the Petri dish after sublimation of the sulphur.\nMANGANIMETRIC DETERMINATION OF EXTRACTED CALCIUM FOLLOW-ING PRECIPITATION IN THE FORM OF OXALATE\n22\nScope\n1 This method is for the determination of calcium in fertiliser extracts.\nField of application\n2 This method applies to all fertilisers for which a declaration of the total and/or water-soluble calcium is required.\nPrinciple\n3 Precipitation of the calcium contained in an aliquot of the extraction solution in the form of an oxalate, which is determined by titration using potassium permanganate.\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\n4.2 1:10 dilute sulphuric acid:\nOne volume of sulphuric acid (d = 1.84 g/ml) in ten volumes of water.\n4.3 1:1 dilute ammonia solution:\nOne volume of ammonia (d = 0.88 g/ml) and one volume of water.\n4.4 Saturated solution of ammonium oxalate [(NH4)2 C2O4 H2O] at ambient temperature (approximately 40 grams per litre).\n4.5 Citric acid solution, 30% (m/v).\n4.6 Ammonium chloride solution, 5% (m/v).\n4.7 Solution of bromothymol blue in 95% ethanol, 0.1% (m/v).\n4.8 Solution of bromocresol green in 95% ethanol 0.04% (m/v).\n4.9 Standard solution of potassium permanganate, 0.02 M.\nApparatus\n5 5.1 Filter crucible with 5 to 20 μ porosity sintered glass.\n5.2 Hot water bath.\nPreparation of the aliquot to be analysed\n6 Using a pipette, take an aliquot portion of the extraction solution obtained by method 17 or 19, containing between 15 and 50 milligrams of Ca (= 21 to 70 milligrams of CaO). Let the volume of this aliquot be v2. Pour into a 400 millilitre beaker. If necessary, neutralise (change of indicator (4.7) from green to blue) with a few drops of the ammonia solution (4.3).\nAnd one millilitre of the citric acid solution (4.5) and five millilitres of ammonium chloride solution (4.6).\nPrecipitation of the calcium oxalate\n7 Add approximately 100 millilitres of water. Bring to boil, add 8 to 10 drops of indicator solution (4.8) and, slowly, 50 millilitres of a hot ammonium oxalate solution (4.4), stirring constantly. If a precipitate forms, dissolve by adding a few drops of hydrochloric acid (4.1). Neutralise very slowly with ammonia solution (4.3) while stirring continuously to a pH of 4.4 to 4.6 (change of indicator (4.8) from green to blue). Place the beaker in a boiling hot water bath (5.2) for approximately 30 minutes.\nRemove the beaker from the bath, leave standing for an hour and filter through the crucible (5.1).\nTitration of the oxalate precipitate\n8 Wash the beaker and crucible until the excess ammonium oxalate has been completely removed (this can be checked by the absence of chloride in the washing water). Place the crucible in the 400 millilitre beaker and dissolve the precipitate with 50 millilitres of hot sulphuric acid (4.2). Add water to the beaker in order to obtain a volume of approximately 100 millilitres. Bring to a temperature of 70 to 80°C and titrate drop by drop with the permanganate solution (4.9) until the pink colour lasts for a minute. Let this volume be n.\nExpression of results\n9 The calcium (Ca) content of the fertiliser is as follows:\nCa (%)=n×0.2004×t0.02×v1v2×m Where:\nn = the volume of 0.2M permanganate used, in millilitres,\nm = the mass of the test sample in grams,\nv2 = the aliquot volume in millilitres,\nv1 = the volume of the extraction solution in millilitres,\nt = the molarity of the permanganate solution in moles per litre.\nCaO (%)=Ca (%)×1.400.\nDETERMINATION OF MAGNESIUM BY ATOMIC ABSORPTION SPEC-TROPHOTOMETRY\n23\nScope\n1 This method is for the determination of magnesium in fertiliser extracts.\nField of application\n2 This method applies to all fertiliser extracts obtained by methods 17 and 19, for which a declaration of the total magnesium and/or water-soluble magnesium is required, with the exception of kieserite, magnesium sulphate, magnesium chloride solution and kieserite with potassium sulphate to which method 24 applies.\nThe method set out below applies to all fertiliser extracts containing elements in quantities that might interfere with the complexometric determination of magnesium.\nPrinciple\n3 Determination of magnesium by atomic absorption spectrophotometry after appropriate dilution of the extract.\nReagents\n4 4.1 Hydrochloric acid, 1M solution.\n4.2 Hydrochloric acid, 0.5M solution.\n4.3 Standard solution of magnesium, 1.00 milligrams per millilitre.\n4.3.1 Dissolve 1.013 grams of magnesium sulphate (MgSO4,7H2O) in 0.5M hydrochloric acid solution (4.2).or:\n4.3.2 weigh out 1.658 grams of magnesium oxide (MgO), previously calcined to remove all traces of carbonation. Place in a beaker with 100 millilitres of water and 120 millilitres of 1M hydrochloric acid (4.1). When it has dissolved, transfer quantitatively into a 1000 millilitre graduated flask. Make up to the volume and mix.\nor:\n4.3.3 Commercial standard solution.\nThe laboratory is responsible for testing such solutions.\n4.4 Strontium chloride solution.\nDissolve 75 grams of strontium chloride (SrCL2 6H2O) in the hydrochloric acid solution (4.2) and make up to 500 millilitres with the same acid solution.\nApparatus\n5 5.1 Spectrophotometer fitted for atomic absorption, with a magnesium lamp, set at 285.2 nm.\n5.2 Air-acetylene flame.\nPreparation of the solution to be analysed\n6 See methods 17 and 19.\nProcedure\n7 7.1 If the fertiliser has a declared magnesium (Mg) content of more than 6&7percnt; (i.e. 10% as MgO), take 25 millilitres (V1) of the extraction solution (6). Transfer into a 100 millilitre graduated flask, and make up to volume with water and mix. The solution factor is D1 = 100/V1.\n7.2 Using a pipette, take 10 millilitres of the extraction solution (6) or the solution (7.1). Transfer into a 200 millilitre graduated flask. Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix. The dilution factor is 200/10.\n7.3 Dilute this solution (7.2) with the 0.5M hydrochloric acid solution (4.2) so as to obtain a concentration in the optimum working field of the spectrophotometer (5.1). V2 is the volume of the sample in 100 millilitres. The dilution factor is D2 = 100/V2.\nThe final solution should contain 10% v/v of the strontium chloride solution (4.4).\n7.4 Preparation of blank solution.\nPrepare a blank solution by repeating the whole procedure from the extraction (method 17 or 19), omitting only the test sample of fertiliser.\n7.5 Preparation of calibration solutions.\nBy diluting the standard solution (4.3) with 0.5M hydrochloric acid, prepare at least five calibration solutions of increasing concentration within the optimum measuring range of the apparatus (5.1).\nThese solutions should contain 10% v/v of the strontium chloride solution (4.4).\n7.6 Measurement.\nSet up the spectrophotometer (5.1) at a wavelength of 285.2 nm.\nSpray, successively, the calibration solutions (7.5), the sample solution (7.3) and the blank solution (7.4), washing the instrument through with the solution to be measured next. Repeat this operation three times. Plot the calibration curve using the mean absorbances of each of the calibration solutions (7.5) as the ordinates and the corresponding concentration of magnesium in μg/ml as the abscissae. Determine the conentration of magnesium in the sample (7.3), Xs and blank (7.4), Xb, by reference to the calibration curve.\nExpression of results\n8 Calculate the amount of magnesium (Mg) or magnesium oxide (MgO) in the sample by reference to the calibration solutions and taking into consideration the blank.\nThe percentage of magnesium (Mg) in the fertiliser is equal to:\nMg (%)(Xs-Xb).D1.(200/10).D2.500.1001000.1000M Where:\nXs = the concentration of the solution as calculated from the calibration curve, in μg/ml.\nXb = the concentration of the blank solution as calculated from the calibration curve, in μg/ml.\nD1 = the dilution factor if the solution is diluted (7.1).\nIt is equal to four if 25 millilitres are taken.\nIt is equal to one when the solution is not diluted.\nD2 = the dilution factor in 7.3.\nM = the mass of the test sample taken for the extraction.\nMgO (%)=Mg (%)/0.6\nDETERMINATION OF MAGNESIUM BY COMPLEXOMETRY\n24\nScope\n1 This method is for the determination of magnesium in fertiliser extracts.\nField of application\n2 This method applies to the determination of total magnesium and/or water-soluble magnesium in the following fertilisers:\nstraight nitrogenous fertilisers (calcium magnesium nitrate, magnesium sulphoni-trate, nitrogenous fertilisers with magnesium) and straight potassic fertilisers (enriched kainite, potassium chloride containing magnesium, potassium sulphate containing magnesium salt), kieserite, magnesium sulphate, magnesium chloride solution, and kieserite with potassium sulphate.\nPrinciple\n3 The magnesium is extracted by methods 17 and/or 19. First titration: with EDTA and Ca and Mg in the presence of Eriochrome black T. Second titration: with EDTA of Ca in the presence of calcein or of calcon carbonic acid. Determination of magnesium by difference.\nReagents\n4 4.1 Standard 0.05M solution of magnesium:\n4.1.1 Dissolve 1.232 grams of magnesium sulphate (MgSO4 7H20) in the 0.5 M hydrochloric acid solution (4.11) and make up to 100 millilitres with the same acid.\nor:\n4.1.2 Weigh out 2.016 grams of magnesium oxide, previously ashed to remove all traces of carbonates. Place it in a beaker with 100 millilitres of water.\nStir in approximately 120 millilitres of approximately 1M hydrochloric acid (4.12).\nAfter dissolution, transfer quantitatively into a graduated 1000 millilitre flask. Make up to volume and mix.\nOne millilitre of these solutions should contain 1.216 milligrams of Mg (= 2.016 milligrams of MgO).\nThe laboratory is responsible for testing the strength of this standard solution.\n4.2 0.05M solution of EDTA.\nWeigh out 18.61 grams of the dihydrated disodium salt of ethylenediaminetet-raacetic (C1and0H1and4N2Na2O82H2O), place it in a 1000 millilitre beaker and dissolve in 600 to 800 millilitres of water. Transfer the solution quantitatively into a graduated 1000 millilitre flask. Make up the volume and mix. Check this solution with the standard solution (4.1) by taking a sample of 20 millilitres of the latter and by titration according to the analytical procedure described at 7.2.\nOne millilitre of the EDTA solution should correspond to 1.216 milligrams of Mg (= 2.016 milligrams of MgO) and to 2.004 milligrams of Ca (= 2.804 milligrams Ca2) (see remarks 10.1 and 10.6).\n4.3 0.05 molar standard solution of calcium.\nWeigh out 5.004 grams of dry calcium carbonate. Place it in a beaker with 100 millilitres of water. Progressively stir in 120 millilitres of approximately 1M hydrochloric acid (4.12).\nBring to the boil in order to drive off the carbon dioxide, cool, transfer quantitatively into a graduated one-litre flask, make up the volume with water and mix. Check this solution against the EDTA solution (4.2) following analytical procedure (8.3). One millilitre of this solution should contain 2.004 milligrams of Ca (= 2.804 milligrams of CaO) and should correspond to one millilitre of the 0.05M EDTA solution (4.2).\n4.4 Calcein indicator.\nCarefully mix in a mortar one gram of calcein with 100 grams of sodium chloride. Use 10 milligrams of this mixture. The indicator changes colour from green to orange. Titration must be carried out until an orange colour free from green tinges is obtained.\n4.5 Calcon carbonic acid indicator.\nDissolve 400 milligrams of calcon carbonic acid in 100 millilitres of methanol. This solution may only be kept for approximately four weeks. Use three drops of this solution. The indicator changes colour from red to blue. Titration must be carried out until a blue colour free from red tinges is obtained.\n4.6 Eriochrome black-T indicator.\nDissolve 300 milligrams of Eriochrome black-T in a mixture of 25 millilitres of propan-1-ol and 15 millilitres of triethanolamine. This solution may only be kept for approximately four weeks. Use three drops of this solution. This indicator changes colour from red to blue and titration must be carried out until a blue colour free from red tinges is obtained. It changes colour only when magnesium is present. If necessary add one millilitre of the standard solution (4.1).\nWhen both calcium and magnesium are present the EDTA first forms a complex with the calcium and then with the magnesium. In that case the two elements are determined concurrently.\n4.7 Potassium cyanide solution.\nAqueous solution of KCN at 2%. (Do not pipette by mouth and see 10.7.)\n4.8 Solution of potassium hydroxide and potassium cyanide.\nDissolve 280 grams of KOH and 66 grams of KCN in water, make up the volume to one litre and mix.\n4.9 pH 10.5 buffer solution.\nIn a 500 millilitre graduated flask, dissolve 33 grams of ammonium chloride in 200 millilitres of water, add 250 millilitres of ammonia (d = 0.91) make up the volume with water and mix. Check the pH of the solution regularly.\n4.10 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\n4.11 Hydrochloric acid solution approximately 0.5M.\n4.12 Hydrochloric acid solution approximately 1M.\n4.13 Sodium hydroxide solution 5 M.\nApparatus\n5 5.1 Magnetic or mechanical stirrer.\n5.2 pH meter.\nControl test\n6 Carry out a determination on aliquots of solutions (4.1 and 4.3) such that the Ca/Mg ratio is approximately equal to that of the solutions to be analysed. To this end take (a) of standard solution (4.3) and (b-a) of standard solution (4.1). (a) and (b) are the volumes of EDTA solution in millilitres used in the two titrations performed on the solution to be analysed. This procedure is correct only if the solutions of EDTA, calcium and magnesium are exactly equivalent. If this is not the case, it is necessary to make corrections.\nPreparation of the solution to be analysed\n7 See methods 17 and 19.\nDetermination\n8 8.1 Aliquot samples to be taken.\nThis aliquot will as far as possible contain between 9 and 18 milligrams of magnesium (= 15 to 30 milligrams of MgO).\n8.2 Titration in the presence of Eriochrome black-T.\nPipette an aliquot (8.1) of the solution to be analysed into a 400 millilitre beaker. Neutralize the excess acid with the 5M sodium hydroxide solution (4.12) and check the pH. Dilute with water to approximately 100 millilitres. Add 5 millilitres of the buffer solution (4.9). The pH measured by the meter must be 10.5 ± 0.1. Add 2 millilitres of the potassium cyanide solution (4.7) and three drops of the Eriochrome black-T indicator (4.6). Titrate with the EDTA solution (4.2). Stirring gently with the stirrer (5.1) (see 10.2, 10.3 and 10.4). Let “b” be the volume in millilitres of 0.05 molar EDTA solution used.\n8.3 Titration in the presence of calcein or of calcon carbonic acid.\nPipette an aliquot of the solution to be analysed equal to that taken for the above titration and place it in a 400 millilitre beaker. Neutralise the excess acid with the 5M sodium hydroxide solution (4.13) using the pH meter. Dilute with water to about 100 millilitres. Add 10 millilitres of the KOH/KCN solution (4.8) and three drops of the indicator (4.4 or 4.5). Stirring gently with the stirrer (5.1) titrate with the EDTA solution (4.2) (see 10.2, 10.3 and 10.4). Let “a” be the volume in millilitres of 0.05M EDTA solution.\nExpression of results\n9 For the EEC fertilisers to which the method is applicable (5 grams of fertiliser in 500 millilitres of extract), the percentage content of the fertiliser is:\nMgO (%) in the fertiliser=(b-a)×TM Mg (%) in the fertiliser=(b-a)×T1M Where:\na = the volume in millilitres of 0.05M EDTA solution used for the titration in the presence of calcein or calcon carbonic acid.\nb = the volume in millilitres of 0.05M EDTA solution used for the titration in the presence of Eriochrome black-T.\nM = the mass of the sample present in the aliquot taken (in grams).\nT = 0.2016 × molarity of the EDTA solution/0.05 (see 4.2).\nT1 = 0.1216 × molarity of the EDTA solution/0.05 (see 4.2).\nRemarks\n10 10.1 The stoichiometric EDTA-metal ratio in the complexometric analyses is always 1:1 whatever the valency of the metal and in spite of the fact that EDTA is quadrivalent. The EDTA titration solution and the standard solutions will therefore be molar and not normal.\n10.2 Complexometric indicators are often sensitive to air. The solution may lose colour during titration. In this case, one or two additional drops of indicator must be added. This is true particularly in the case of Eriochrome black-T and calcon carbonic acid.\n10.3 The metal-indicator complexes are often relatively stable and it may take some time for the colour to change. The last drops of EDTA must therefore be added slowly and a drop of 0.05 molar solution of magnesium (4.1) or calcium (4.3) added to ensure that the colour change has not already taken place. This is particularly true in the case of the eriochrome-magnesium complex.\n10.4 The colour change of the indicator must not be observed vertically, but horizontally across the solution and the beaker must be placed against a white background in a well-lit position. The colour change of the indicator may also be observed easily by placing the beaker on frosted glass lit moderately from below (25 watt lamp).\n10.5 This analysis requires a certain amount of experience. The task will involve, among other things, observing the colour changes of standard solutions 4.1 and 4.3. It is recommended that the determinations be carried out by the same laboratory chemist.\n10.6 If an EDTA solution of guaranteed strength is used (Titrisol, Normex, for example) this may simplify the control of the equivalence of standard solutions 4.1, 4.2 and 4.3.\n10.7 The solutions containing potassium cyanide must not be poured down the sink until the cyanide has been converted into a harmless compound, for example, by oxidation with sodium hypochlorite after having been made alkaline.\nDETERMINATION OF SULPHATES\n25\nScope\n1 This method is for the determination of sulphur present in fertiliser extracts in the form of sulphates.\nField of application\n2 This method applies to the determination of sulphates present in the extractions performed in methods 17, 18, 19 and 20.\nPrinciple\n3 Gravimetric determination as barium sulphate.\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) and one volume of water.\n4.2 Barium chloride solution BaC12. 2H2O:122 grams per litre.\n4.3 Silver nitrate solution: 5 grams per litre.\nApparatus\n5 5.1 Crucibles.\n5.2 Hot water bath.\n5.3 Drying oven set at 105°C ± 1°C.\n5.4 Electric furnace set at 800°C ± 50°C.\nProcedure\n6 6.1 Sampling of the solution.\nPipette an aliquot of one of the extraction solutions indicated at 2 containing between 20 and 100 milligrams of S or 50 and 250 milligrams of SO3.\nPlace this aliquot in a beaker of suitable capacity. Add 20 millilitres of dilute hydrochloric acid (4.1). Make up to about 300 millilitres with water.\n6.2 Preparation of the precipitate.\nBring the solution to the boil. Add, drop by drop, about 20 millilitres of the hot barium chloride solution (4.2) while stirring the solution vigorously. Boil for a few minutes.\nPlace the beaker, covered with a watch glass, in a boiling water bath (5.2) for an hour. Then leave standing hot (~60°C) until the supernatant liquor is clear. Decant the clear solution through a slow filtration ash-free filter. Wash the precipitate several times with hot water. Continue to wash the precipitate on the filter until the filtrate is chloride free. This can be checked by using silver nitrate solution (4.3).\n6.3 Incineration and weighing of the precipitate.\nPlace the filter paper and precipitate in a crucible (5.1) previously weighed to the nearest 0.1 milligrams. Dry in the oven (5.3) and ash at approximately 800°C for half an hour (5.4). Allow to cool in a desiccator and weigh to within 0.1 milligrams.\nExpression of results\n7 One milligram of barium sulphate corresponds to 0.137 milligrams of S or to 0.343 milligrams of SO3.\nThe percentage S content of the fertiliser is obtained as follows:\nS(%)=w×0.0137×v1v2×m SO3(%)=S(%)×2.5 Where:\nw = the mass of the barium sulphate precipitate in milligrams,\nv1 = the volume of the extraction solution in millilitres,\nv2 = the aliquot volume in millilitres,\nm = the mass of the test sample in grams.\nDETERMINATION OF THE SODIUM EXTRACTED\n26\nScope\n1 This method is for the determination of sodium in fertiliser extracts.\nField of application\n2 This method applies to fertilisers for which a declaration of sodium is required.\nPrinciple\n3 Following suitable dilution of the extract obtained via method 17 and/or 19 the sodium content of the solution is determined by flame-emission spectrophotometry.\nReagents\n4 4.1 Diluted hydrochloric acid:\nOne volume of hydrochloric acid (d = 1.18 g/ml) plus one volume of water.\n4.2 Aluminium nitrate Al(NO3)3,9H2O.\n4.3 Caesium chloride, CsCl.\n4.4 Anhydrous sodium chloride, NaCl.\n4.5 Caesium chloride and aluminium nitrate solution.\nDissolve in water 50 grams of caesium chloride (4.3) and 250 grams of aluminium nitrate (4.2) in a 1000 millilitre graduated flask. Make up to volume with water and mix.\n4.6 Standard sodium solution of one milligram/millilitre of Na.\nDissolve in water 2.542 grams of sodium chloride (4.4) in a 1000 millilitre graduated flask. Add 10 millilitres of hydrochloric acid (4.1). Make up to volume with water and mix.\nApparatus\n5 Spectrophotometer equipped for flame emission, set at 589.3 nm.\nCalibration solutions\n6 6.1 Pipette 10 millilitres of standard solution (4.6) into a 250 millilitre graduated flask. Make up to volume and mix. Concentration of solution: 40 μg/ml of Na.\n6.2 Using a burette place 0, 5, 10, 15, 20, 25 millilitres of the intermediate solution (6.1) in 100 milliltres graduated flasks. Add 10 millilitres of the solution (4.5). Make up to volume and mix. Concentration of solutions: 0, 2, 4, 6, 8, 10 μg/ml of Na.\nPreparation of solutions to be measured\n7 Depending upon the expected sodium content of the extraction solution as in method 17 or 19 (five grams of fertiliser in 500 millilitres), carry out the dilutions in accordance with the following table:\nNa2O (%)\nNa (%)\nIntermediate dilution\nSample (ml) (v2)\nDilution to ml (v3)\nFinal dilution\nSample (ml) (v4)\nDilution to ml\nDegree of dilution\n3–5\n2.2–3.7\n10\n50\n10\n100\n50\n5–10\n3.7–7.4\n10\n100\n10\n100\n100\n10–20\n7.4–15\n10\n100\n5\n100\n200\n20–38\n15–28\n5\n100\n5\n100\n400\nMake up the intermediate dilution with water. For the final dilution add ten millilitres of the solution (4.5) to the 100 millilitre graduated flask.\nFor a test sample of one gram multiply the volume of the final dilution (V4) by five.\nDetermination\n8 Prepare the spectrophotometer (5) for the measurements at 589.3 nm. Calibrate the instrument by measuring the response of the calibration solutions (6.2). Then adjust the sensitivity of the instrument to use its entire scale when the most concentrated calibration solution is used. Then measure the response of the sample solution to be analysed (7). Repeat this operation twice.\nCalculation of results\n9 Draw a calibration curve by plotting the average response for each calibration solution along the ordinate and the corresponding concentrations, expressed in μg per millilitre on the abscissa. Determine from this the sodium concentration of the test solution. Calculate the quantity of sodium from the standard solutions taking account of the levels of dilution. Express the results as a percentage of the sample.\nThe percentage sodium (Na) content of the fertiliser is as follows:\nNa(%)=xv3v4v1v210-2m Na2O(%)=Na(%)×1.348 Where:\nx = the concentration of the solution introduced into the spectrophotometer in μg/ml,\nv1 = the volume of the extraction solution in millilitres,\nv2 = the aliquot volume in the intermediate dilution in millilitres,\nv3 = the volume of intermediate dilution in millilitres,\nv4 = the aliquot volume in ml of the final dilution (in 100 millilitres),\nm = the mass of the test sample in grams.”",
  "extent": null,
  "status": null,
  "version": "current",
  "annotations": [],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/uksi/1991/2824/schedule/3",
    "retrieved_at": "2026-10-29T14:32:33.653567+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}