1、BRITISH STANDARD BS 7755-3.7: 1995 ISO 11261: 1995 Soil quality Part 3: Chemical methods Section 3.7 Determination of total nitrogen Modified Kjeldahl methodBS7755-3.7:1995 This British Standard, having been prepared under the directionof the Health and Environment Sector Board, was published under
2、the authority ofthe Standards Board and comesinto effect on 15 October 1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference EH/4/3 Draft for comment 93/502663 DC ISBN 0 580 24691 4 Committees responsible for this British Standard The preparation of t
3、his British Standard was entrusted by Technical Committee EH/4, Soil quality, to Subcommittee EH/4/3, Chemical methods, upon which the following bodies were represented: Association of Consulting Scientists Association of Public Analysts British Ceramic Research Ltd. British Gas plc British Society
4、of Soil Science Department of the Environment (Drinking Water Inspectorate) Department of Trade and Industry (Laboratory of the Government Chemist) National Rivers Authority Royal Society of Chemistry Society of Chemical Industry Soil Survey and Land Research Centre Water Research Centre Water Servi
5、ces Association of England and Wales Amendments issued since publication Amd. No. Date CommentsBS7755-3.7:1995 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Pretreatment of soil
6、 samples 1 7 Procedure 1 8 Calculation of the result 2 9 Precision 2 10 Test report 2 Annex A(informative) Bibliography 4 Table 1 General average of nitrogen content, s r , r, s Rand R calculatedafterelimination of outliers 3 List of references Inside back coverBS7755-3.7:1995 ii BSI 10-1999 Nationa
7、l foreword This British Standard has been prepared by Subcommittee EH/4/3 and is identical with ISO 11261:1995 Soil quality Determination of total nitrogen Modified Kjeldahl method, published by the International Organization for Standardization (ISO). ISO 11263 was prepared by Subcommittee 3, Chemi
8、cal methods, of Technical Committee ISO/TC 190, Soil quality, with the active participation and approval of the UK. BS 7755 is being published in a series of Parts subdivided into Sections and Subsections that will generally correspond to particular International Standards. Other Parts of BS 7755 ar
9、e, or will be, as follows. Part 1: Terminology and classification; Part 2: Sampling; Part 3: Chemical methods; Part 4: Biological methods; Part 5: Physical methods. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible f
10、or their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 3696:1987 BS 3978:1987 Specification for water for laboratory use (Identical) ISO 5725:1986 BS 5497 P
11、recision of test methods Part1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (Identical) BS 7755 Soil quality ISO 11464:1994 Section 3.5:1995 Pretreatment of samples for physico-chemical analyses (Identical) ISO 11465:1993
12、Section 3.1:1994 Determination of dry matter and water content on a mass basis by a gravimetric method (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, an inside back cover and a back cover. This standard has been updated (see copyr
13、ight date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7755-3.7:1995 BSI 10-1999 1 1 Scope This International Standard specifies a method for the determination of the total nitrogen (ammonium-N, nitrate-N, nitrite-N and organic
14、N) content of a soil. Nitrogen in N-N-linkages, N-O-linkages and some heterocyclics (especially pyridine) is only partially determined. ThisInternational Standard is applicable to all types of soils. 2 Normative references The following standards contain provisions which, through reference in this t
15、ext, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent ed
16、itions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 3696:1987, Water for analytical laboratory use Specification and test methods. ISO 5725:1986, Precision of test methods Determination of repeatability and reproducibilit
17、y for a standard test method by inter-laboratory tests. ISO 11464:1994, Soil quality Pretreatment of samples for physico-chemical analyses. ISO 11465:1993, Soil quality Determination of dry matter and water content on a mass basis Gravimetric method. 3 Principle The method is based on the Kjeldahl-d
18、igestion, but titanium dioxide (TiO 2 ) is used as the catalyst instead of selenium. NOTE 1Titanium dioxide is ecotoxicologically less harmfull than selenium. 4 Reagents All reagents shall be of recognized analytical grade. Use water of grade 2 complying with ISO 3696. 4.1 Salicylic acid/sulfuric ac
19、id Dissolve 25 g of salicylic acid in 1 litre of concentrated sulfuric acid ( = 1,84 g/cm 3 ). 4.2 Potassium sulfate catalyst mixture Grind and thoroughly mix 200 g of potassium sulfate, 6 g of copper(II) sulfate pentahydrate and6g of titanium dioxide, with the crystal structure of anatase. 4.3 Sodi
20、um thiosulfate pentahydrate Crush the crystals to form a powder that passes through a sieve with an aperture of 0,25 mm. 4.4 Sodium hydroxide, c(NaOH) = 10 mol/l. 4.5 Boric acid solution, (H 3 BO 3 ) = 20 g/l. 4.6 Mixed indicator Dissolve 0,1 g of bromocresol green and 0,02 g of methyl red in 100 ml
21、 of ethanol. 4.7 Sulfuric acid, c(H + ) = 0,01 mol/l. 5 Apparatus Usual laboratory equipment and 5.1 Digestion flasks or tubes, of nominal volume50ml, suitable for the digestion stand. 5.2 Digestion stand NOTE 2Glass tubes placed in holes drilled into an aluminium block are also suitable. 5.3 Distil
22、lation apparatus, preferably of the Parnas-Wagner type. 5.4 Burette, graduated in intervals of 0,01 ml or smaller. 6 Pretreatment of soil samples Samples shall be pretreated according to ISO 11464. NOTE 3Losses of nitrogen can occur with samples of high ammonium-N and nitrate-N content. Therefore, e
23、xcessive drying(105 C) should be avoided. 7 Procedure Place a test portion of the air-dried soil sample, of about 0,2 g (expected nitrogen content . 0,5 %) to1g (expected nitrogen content . 0,1 %), in the digestion flask (5.1). Add 4 ml of salicylic/sulfuric acid (4.1) and swirl the flask until the
24、acid is thoroughly mixed with the soil. Allow the mixture to stand for at least several hours (or overnight). Add0,5 g of sodium thiosulfate (4.3) through a dry funnel with a long stem that reaches down into the bulb of the digestion flask, and heat the mixture cautiously on the digestion stand (5.2
25、) until frothing has ceased. Then cool the flask, add 1,1 g of the catalyst mixture(4.2) and heat until the digestion mixture becomes clear. Boil the mixture gently for up to 5 h so that the sulfuric acid condenses about 1/3 of the way up to the neck of the flask. Ensure that the temperature of the
26、solution does not exceed 400 C. NOTE 4In most cases a boiling period of 2 h is sufficient.BS7755-3.7:1995 2 BSI 10-1999 After completion of the digestion step, allow the flask to cool and add about 20 ml of water slowly while shaking. Then swirl the flask to bring any insoluble material into suspens
27、ion and transfer the contents to the distillation apparatus (5.3). Rinse three times with water to complete the transfer. Add5 ml of boric acid (4.5) to a 100 ml conical flask and place the flask under the condenser of the distillation apparatus in such a way that the end of the condenser dips into
28、the solution. Add 20 ml of sodium hydroxide (4.4) to the funnel of the apparatus and run the alkali slowly into the distillation chamber. Distil about 40 ml of condensate (the amount for quantitative results depends on the dimensions of the apparatus), rinse the end of the condenser, add a few drops
29、 of indicator (4.6) to the distillate and titrate with sulfuric acid (4.7) to a violet endpoint. NOTE 5A potentiometric titration is also possible. The endpoint of the titration should be pH = 5,0. NOTE 6If steam distillation is used, a distillation rate of up to about 25 ml/min is applicable. Stop
30、the distillation when about100 ml of distillate have been collected. Carry out a blank test in which the same procedure is performed without soil. Notify the consumption of sulfuric acid in the blank test and in the tests of the soil samples. 8 Calculation of the result The total content of nitrogen
31、, (w N ), in milligrams per gram, is calculated using the formula: Round the result to two significant figures. 9 Precision The precision data according to ISO 5725 were determined from an experiment conducted in 1992 involving 14 laboratories and 4 soil samples. The results obtained are given in Ta
32、ble 1. From the data in Table 1, it can be concluded that the difference between two separate determinations should not exceed 15 % of the measured total nitrogen content when the content is less than 2 mg/g, and 10 % of the measured total nitrogen content when the content is greater than 2 mg/g. 10
33、 Test report The test report shall contain the following information: a) a reference to this International Standard; b) a complete identification of the sample; c) the results of the determination; d) any details not specified in this International Standard or which are optional, as well as any fact
34、or which may have affected the results. where V 1 is the volume, in millilitres, of the sulfuric acid (4.7) used in the titration of the sample indicator (4.6); V 0 is the volume, in millilitres, of the sulfuric acid (4.7) used in the blank test indicator(4.6); c(H + ) is the concentration of H +in
35、the sulfuric acid (4.7), in moles per litre e.g. if 0,01 mol/l sulfuric acid is used, c(H + ) = 0,02 mol/l; M N is the molar mass of nitrogen, in grams per mole (= 14); m is the mass, in grams, of the air-dried sample of soil; is the water content, expressed as a percentage by mass, on the basis of
36、oven-dried soil, determined according to ISO 11465. w H 2 OBS7755-3.7:1995 BSI 10-1999 3 Table 1 General average of nitrogen content, s r , r, s Rand R calculated after elimination of outliers Sample No. Nitrogen content, w N mg/g Repeatability conditions of soil mg/g Reproducibility conditions mg/g
37、 s r r s r R 1 0,98 0,06 0,17 0,27 0,76 2 3,11 0,12 0,33 0,58 1,62 3 6,70 0,19 0,54 1,07 3,00 4 10,88 0,26 0,74 0,89 2,50 s ris the repeatability standard deviation r is the repeatability value s Ris the reproducibility standard deviation R is the reproducibility valueBS7755-3.7:1995 4 BSI 10-1999 A
38、nnex A (informative) Bibliography 1 THUN, HERRMANN and KNICKMANN, Die Untersuchung von Bden (1955), Neumann Verlag, Radebeul und Berlin. 2 PAGE, A.L. et al., Methods of soil analysis, Part 2 (1982). American Society of Agronomy and Soil Science of America, Madison, WI. 3 WILLIAMS, P.C. J. Sci. Fd. A
39、gric. 24 (1973), p. 343.BS7755-3.7:1995 BSI 10-1999 List of references See national foreword.BS 7755-3.7: 1995 ISO 11261: 1995 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK v
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