1、BRITISH STANDARD BS5551-4.1.3: 1986 ISO5315:1984 Fertilizers Part4: Chemical analysis Section4.1 Determination of nitrogen Subsection4.1.3 Method for determination of total nitrogen content (titrimetric method after distillation) ISO title: Fertilizers Determination of total nitrogen content Titrime
2、tric method after distillation UDC 631.8:543.06:543.24:546.17BS5551-4.1.3:1986 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, waspublished under the authorityofthe Board of BSIandcomes intoeffect on 31July1986 BSI10-1999 The following BSI referen
3、ces relate to the work on this standard: Committee reference CIC/37 Draft for comment82/52594 DC ISBN 0 580 15219 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Committee (CIC/-) to Technical Committee CIC/37 upon
4、which the following bodies were represented: Association of Public Analysts Department of Trade and Industry (Laboratory of the Government Chemist) Fertiliser Manufacturers Association Ltd Institute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food Amendments issued sin
5、ce publication Amd. No. Date of issue CommentsBS5551-4.1.3:1986 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and field of application 1 2 Principle 1 3 Reagents 1 4 Apparatus 1 5 Procedure 2 6 Expression of results 3 7 Test report 4 Figure Typica
6、l distillation apparatus 5 Table 2 Publications referred to Inside back coverBS5551-4.1.3:1986 ii BSI 10-1999 National foreword This Subsection of BS5551 has been prepared under the direction of the Chemicals Standards Committee in order to standardize the determination of nitrogen in fertilizers. F
7、or some years the United Kingdom has participated in the standardization of methods of analysing fertilizers through Subcommittee4, Chemical analysis, of Technical Committee134, Fertilizers and soil conditioners, of the International Organization for Standardization (ISO). As international agreement
8、 is reached on the methods, it is proposed to publish them as Sections of BS5551. The standard is published in four Parts, each Part being subdivided into Sections and, where appropriate, Subsections. The four Parts are: Part1: Terminology and labelling; Part2: Sampling; Part3: Physical properties;
9、Part4: Chemical analysis. Part4 is to be divided into five Sections as follows. Section4.1: Determination of nitrogen; Section4.2: Determination of phosphorus; Section4.3: Determination of potassium; Section4.4: Determination of water; Section4.5: Determination of other constituents. This Subsection
10、 of Part4 is identical with ISO5315:1984 “Fertilizers Determination of total nitrogen content Titrimetric method after distillation”. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some termin
11、ology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Whereve
12、r the words “International Standard” or “ISO5315”, appear, referring to this standard, they should be read as “British Standard” or “BS5551-4.1.3” respectively. In British Standards it is current practice to use the symbol “L” for litre (and in its submultiples), rather than “l”, and to use the spel
13、ling “sulphur”, etc.,instead of “sulfur”, etc. Cross-reference. With reference to4.4, burettes of capacity50mL complying with the requirements for class A of BS846 “Specification for burettes” will be suitable. Additional information. 1) This British Standard describes a method of test only and shou
14、ld not be used as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance with BS5551-4.1.3.BS5551-4.1.3:1986 BSI 10-1999 iii 2) Until the International Standard, referred to in the note to5.1, on the sampling of fertilizers
15、is available, guidance can be found in Part1“Introduction and general principles”, and Part4 “Sampling of solids”, of BS5309 “Methods for sampling chemical products”. 3) With reference to clause3, water complying with BS3978 “Water for laboratory use” is suitable. A British Standard does not purport
16、 to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cove
17、r, pagesi toiv, pages1to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS5551-4.1.3:1986 BSI 10-1999 1 1 Scope and field of applica
18、tion This International Standard specifies a titrimetric method, after distillation, for the determination of the total nitrogen content of fertilizers in all forms, including those which have to be digested. The method is not recommended for fertilizers containing more than7% of organic matter. 2 P
19、rinciple Reduction of nitrate to ammonia by chromium powder in acid medium. Conversion of organic and urea nitrogen into ammonium sulfate by digestion with concentrated sulfuric acid in the presence of a catalyst. Distillation of the ammonia from an alkaline solution, absorption in an excess of stan
20、dard volumetric sulfuric acid solution and back-titration with standard volumetric sodium hydroxide solution in the presence of methyl red or screened methyl red as indicator. 3 Reagents During the analysis, use only reagents of recognized analytical grade having, in particular, low nitrogen content
21、s (see5.3), and only distilled water or water of equivalent purity. 3.1 Chromium metal, powder, of particle size less than or equal to250 4m. 3.2 Aluminium oxide, fused. Pumice is suitable. 3.3 Anti-foaming agent, for example paraffin wax of melting point not lower than100 C, or a silicone. 3.4 Ammo
22、nium nitrate, dried at100 C to constant mass. 3.5 Digestion catalyst mixture, finely ground, comprising potassium sulfate (K 2 SO 4 ):1000g; copper(II) sulfate pentahydrate (CuSO 4 .5H 2 O):50g. 3.6 Sulfuric acid, concentrated, approximately1,84g/ml. 3.7 Hydrochloric acid, concentrated, approximatel
23、y1,18g/ml. 3.8 Sodium hydroxide, approximately400g/l solution. 3.9 Sodium hydroxide, standard volumetric solution, c(NaOH)=0,10mol/l. 1) 3.10 Sulfuric acid, standard volumetric solution, c(H 2 SO 4 )=0,25mol/l. 2) 3.11 Sulfuric acid, standard volumetric solution, c(H 2 SO 4 )=0,10mol/l. 3) 3.12 Sulf
24、uric acid, standard volumetric solution, c(H 2 SO 4 )=0,05mol/l. 1) 3.13 Indicator, solution. Use either the screened methyl red solution(3.13.1) or the methyl red solution(3.13.2). 3.13.1 Screened methyl red, ethanolic indicator solution. Mix50ml of a2g/l ethanolic solution of methyl red with50ml o
25、f a1g/l ethanolic solution of methylene blue. 3.13.2 Methyl red, ethanolic indicator solution. Dissolve0,1g of methyl red in50ml of95% (V/V) ethanol. 3.14 pH indicator paper, wide range. 4 Apparatus Usual laboratory equipment, and 4.1 Digestion apparatus, comprising an800ml Kjeldahl flask and a pear
26、-shaped hollow glass stopper. 4.2 Distillation apparatus The components of the distillation apparatus may be connected by means of rubber bungs and tubing or by the use of spherical ground glass joints. Spherical ground glass joints should be held by spring clamps to ensure that they are leak-tight.
27、 Rubber bungs and tubing shall be replaced when they begin to perish or show signs of wear. A suitable apparatus is illustrated in the Figure and comprises the following components. 4.2.1 Flask Either the Kjeldahl flask(4.1) or1000ml round-bottomed flask may be used. 4.2.2 Single-bulb splash head an
28、d separate open-top dropping funnel, of capacity100ml, followed by a delivery tube at the outlet. 4.2.3 Allihn condenser, seven bulb (or other suitable condenser), with an expansion bulb, of approximate capacity100ml, followed by a delivery tube at the outlet. 4.2.4 Receiver: conical flask or beaker
29、, of capacity500ml. 4.3 Anti-bumping granules or an anti-bumping device consisting of a100mm 5mm glass rod connected to a25mm length of polyethylene tubing. 4.4 Two burettes, of capacity50ml, complying with the requirements of ISO385-1, class A. 4.5 Glass beads, of diameter2 to3mm. 1) Hitherto expre
30、ssed as“0,10N standard volumetric solution”. 2) Hitherto expressed as“0,50N standard volumetric solution”. 3) Hitherto expressed as“0,20N standard volumetric solution”.BS5551-4.1.3:1986 2 BSI 10-1999 5 Procedure 5.1 Test portion Weigh, to the nearest0,001g, between0,5 and2,0g of the test sample, con
31、taining not more than60mg of nitrate nitrogen and235mg of total nitrogen. NOTEThe preparation of test samples of fertilizers will form the subject of a future International Standard. 5.2 Determination 5.2.1 Reduction (this step is not required if nitrate nitrogen is known to be absent) Transfer the
32、test portion(5.1) to the flask(4.1) and add sufficient water to make up the total volume to35ml. Allow the flask to stand for10min with occasional gentle swirling to ensure dissolution of all nitrate salts. Add1,2g of the chromium powder(3.1) and7ml of the hydrochloric acid solution(3.7). Allow the
33、flask to stand for at least5min, but not more than10min, at ambient temperature. Place the flask on a heating device in a fume cupboard with the heat input regulated to pass a7 to7,5min boil test 4) and heat the flask for4,5min. Remove from the heat and allow to cool. 5.2.2 Hydrolysis this step can
34、be used instead of the digestion(5.2.3) if it is known that the only forms of organic nitrogen present are urea and cyanamide forms Stand the flask in a fume cupboard and add1,5g of the fused aluminium oxide(3.2). Carefully add25ml of the sulfuric acid(3.6) to the flask. Insert the pear-shaped hollo
35、w glass stopper into the neck of the flask and place on a heating device and initially heat until gently boiling. Then adjust the heat input to pass a7 to7,5min boil test. 4) Continue to heat the flask and contents until dense white fumes of sulfuric acid have been evolving for at least15min. Allow
36、the flask to cool to room temperature and carefully add250ml of water. Allow the flask to cool. 5.2.3 Digestion this step is necessary only if organic forms of nitrogen other than urea or cyanamide forms are present (see5.2.2) or in the case of fertilizers of unknown composition Place the flask in a
37、 fume cupboard and add22g of the digestion catalyst mixture(3.5) and1,5g of the fused aluminium oxide(3.2). Carefully add30ml of the sulfuric acid(3.6) to the flask and add0,5g of the anti-foaming agent(3.3) to reduce foaming. Insert the pear-shaped hollow glass stopper into the neck of the flask an
38、d place on a heating device with the heat input adjusted to pass a7 to7,5min boil test. 4) If considerable foaming occurs, reduce the heat input until this phase is over. Continue to heat the flask and contents until dense white fumes are cleared from the bulb of the flask. Gently swirl the flask an
39、d continue digestion for a further60min or until the solution is clear, whichever is the longer. Allow the flask to cool to room temperature and carefully add250ml of water. Allow the flask to cool. 5.2.4 Distillation If distillation from the round-bottomed flask is preferred, transfer the test port
40、ion(5.1) or the hydrolysed(5.2.2) or digested(5.2.3) solution to it quantitatively. Otherwise, place the test portion, or retain the solution, in the Kjeldahl flask. Place the anti-bumping granules or anti-bumping device(4.3), in the latter case with the polyethylene in contact with the bottom of th
41、e flask, in the flask, and add a few of the glass beads(4.5). Assemble the apparatus as shown in the Figure. Measure into the receiver(4.2.4), according to the expected mass of nitrogen in the test portion, the appropriate volume shown in the Table of one of the sulfuric acid solutions(3.10, 3.11 or
42、3.12). Table Add4 or5drops of the indicator solution(3.13) and place the receiver so that the end of the delivery tube is below the surface of the acid, adding water to the receiver if necessary. 4) The heat input is that required to bring250ml of water at25 C to a “rolling” boil in7 to7,5min. Expec
43、ted mass of nitrogen in the test portion Concentration of sulfuric acid solution Volume of sulfuric acid solution mg mol/l ml 0 to 30 30 to 50 50 to 65 0,5 (solution 3.12) 25,0 40,0 50,0 65 to 80 80 to100 100 to125 0,10 (solution3.11) 35,0 40,0 50,0 125 to170 170 to200 200 to235 0,25 (solution3.10)
44、25,0 30,0 35,0BS5551-4.1.3:1986 BSI 10-1999 3 Pour at least120ml of the sodium hydroxide solution(3.8), or20ml if there was neither hydrolysis(5.2.2) nor digestion(5.2.3), into the dropping funnel and carefully run all but about2ml of this solution into the distillation flask. Close the stop-cock, l
45、eaving the remaining2ml in the dropping funnel. Bring the contents of the flask to the boil, increasing the rate of heating progressively until, finally, the contents of the flask are boiling briskly. The contents of the flask shall remain alkaline during the distillation period. When at least150ml
46、of distillate have been collected, partially withdraw the receiver so that the delivery tube rests on the rim of the receiver. Test the subsequent distillate with the pH indicator paper(3.14) to ensure that all the ammonia is completely distilled. Remove the source of heat. Detach the splash head fr
47、om the condenser and wash the insides of the condenser and expansion bulb with water, collecting the rinsings in the receiver. Also rinse the outside of the delivery tube and collect the rinsings in the receiver. 5.2.5 Titration Back-titrate the excess of acid with the standard volumetric sodium hyd
48、roxide solution(3.9) to the neutral colour of the indicator. 5.3 Blank test Carry out a blank test, at the same time as the determination, using the same procedure, using the same reagents, but omitting the test portion, and using the0,05mol/l standard volumetric sulfuric acid solution(3.12). The re
49、sult of the blank test should not exceed1,0ml of standard volumetric solution. If the result is greater than1,0ml, check the reagents, especially the chromium powder(3.1). 5.4 Check test Carry out a periodic check on the efficiency of the apparatus and the accuracy of the method using an aliquot portion of a solution of freshly prepared ammonium nitrate(3.4) containing100mg of nitrogen. The check shall be made using the same conditions as for the determination and the blank test and using the same indicator. 6 Expression of res
