ISO-11261-1995.pdf

INTERNATIONAL STANDARD IS0 11261 First edition 1995-03-01 Soil quality - Determination of total nitrogen - Modified Kjeldahl method Qualit du sol - Dosage de I azote total - MBthode de Kjeldahl modifike Reference number IS0 11261 :I 995(E) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11261:1995(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 11261 was prepared by Technical Committee lSO/rC 190, Soil quality, Subcommittee SC 3, Chemical methods and soil characteristics. Annex A of this International Standard is for information only. 8 IS0 1995 All nghts reserved. Unless otherwise specified, no part of this publication may be reproduced or utlllzed in any form or by any means, electronic or mechanical, lncludlng photocopytng and microftlm, without permlssron in writing from the publisher. InternatIonal Organization for Standardlzatlon Case Postale 56 l CH-1211 Genhve 20 l Switzerland Pnnted in Switzerland ii Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD Q IS0 IS0 11261:1995(E) Soil quality - Determination of total nitrogen - Modified Kjeldahl method 1 Scope This International Standard specifies a method for the determination of the total nitrogen (ammonium-N, nitrate-N, nitrite-N and organic N) content of a soil. Nitrogen in N-N-linkages, N-O-linkages and some het- erocyclics (especially pyridine) is only partially deter- mined. This International Standard is applicable to all types of soils. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, 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 re- cent editions of the standards indicated below. Members of IEC and IS0 maintain registers of cur- rently valid International Standards. IS0 3696:1987, Water for analytical laboratory use - Specification and test methods. IS0 5725:1986, Precision of test methods - Deter- mination of repeatability and reproducibility for a standard test method by inter-laboratory tests. IS0 11464: 1994, Soil quality - Pretreatment of sam- ples for ph ysico-chemical analyses. IS0 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-digestion, but titanium dioxide (TiO,) is used as the catalyst instead of selenium. NOTE 1 Titanium dioxide is ecotoxicologically less harmfull than selenium. 4 Reagents All reagents shall be of recognized analytical grade. Use water of grade 2 complying with IS0 3696. 4.1 Salicylic acid/sulfuric acid. Dissolve 25 g of salicylic acid in 1 litre of concentrated sulfuric acid (e = I,84 g/cm3). 4.2 Potassium sulfate catalyst mixture. Grind and thoroughly mix 200 g of potassium sulfate, 6 g of copper sulfate pentahydrate and 6 g of titanium dioxide, with the crystal structure of anatase. 4.3 Sodium 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, p(H,BO,) = 20 g/l. 4.6 Mixed indicator. Dissolve 0,l g of bromocresol green and 0,02 g of methyl red in 100 ml of ethanol. 4.7 Sulfuric acid, c(H+) = 0,Ol mol/l. 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11261:1995(E) 63 IS0 5 Apparatus Usual laboratory equipment and 5.1 Digestion flasks or tubes, of nominal volume 50 ml, suitable for the digestion stand. 5.2 Digestion stand. NOTE 2 Glass tubes placed in holes drilled into an alu- minium block are also suitable. 5.3 Distillation apparatus, preferably of the Parnas-Wagner type. 5.4 Burette, graduated in intervals of 0,Ol ml or smaller. 6 Pretreatment of soil samples Samples shall be pretreated according to IS0 11464. NOTE 3 Losses of nitrogen can occur with samples of high ammonium-N and nitrate-N content. Therefore, ex- cessive 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 z 0,5 %) to 1 g (expected nitrogen content = 0,l %), in the di- gestion flask (5.1). Add 4 ml of salicylic/sulfuric acid (4.1) and swirl the flask until the acid is thoroughly mixed with the soil. Allow the mixture to stand for at least several hours (or overnight). Add 0,5 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) until frothing has ceased. Then cool the flask, add 1,l 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 l/3 of the way up to the neck of the flask. Ensure that the temperature of the solution does not exceed 400 “C. NOTE 4 In most cases a boiling period of 2 h is sufficient. 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 suspension and transfer the contents to the distillation apparatus (5.3). Rinse three times with water to complete the transfer. Add 5 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 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 de- pends on the dimensions of the apparatus), rinse the end of the condenser, add a few drops of indicator (4.6) to the distillate and titrate with sulfuric acid (4.7) to a violet endpoint. NOTE 5 A potentiometric titration is also possible. The endpoint of the titration should be pH = 5,0. NOTE 6 If steam distillation is used, a distillation rate of up to about 25 ml/min is applicable. Stop the distillation when about 100 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, (w,), in milligrams per gram, is calculated using the formula: w N = (v, -0) xc(H+) x”N x 1oo+wH20 m 100 where Vl is the volume, in millilitres, of the sulfuric acid (4.7) used in the titration of the sample indicator (4.6)1; VO is the volume, in acid (4.7) used in (4.6); millilitres, of the sulfuric the blank test indicator is the concentration of H+ in the sulfuric acid (4.71, in moles per litre e.g. if 0,Ol mol/l sulfuric acid is used, c(H+) = 0,02 mol/l; is the molar mass of nitrogen, in grams per mole (= 14); m is the mass, in grams, of the air-dried sample of soil; wH20 is the water content, expressed as a per- centage by mass, on the basis of oven- dried soil, determined according to IS0 11465. Round the result to two significant figures. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 11261:1995(E) 9 Precision The precision data according to IS0 5725 were de- termined from an experiment conducted in 1992 in- volving 14 laboratories and 4 soil samples. The results obtained are given in table 1. 10 Test report The test report shall contain the following information: a) a reference to this International Standard; 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 nitro- gen 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. 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 factor which may have affected the results. Table 1 - General average of nitrogen content, s, r, sR and R calculated after elimination of outliers Nitrogen content, w, Repeatability conditions of soil Reproducibility conditions Sample No. wig mglg mclg -% r SR R 1 0.98 0.06 0.17 0.27 0.76 2 3,l 1 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, is the repeatability standard deviation S, is the reproducibility standard deviation r is the repeatability value R is the reproducibility value 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11261:1995(EI Annex A (informative) Bibliography l THUN, HERRMANN and KNICKMANN, Die Untersuchung von Bidden (19551, 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. 33 WILLIAMS, P.C. J. Sci. Fd. Agric. 24 (1973, P. 343. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11261:1995(E) Q IS0 ICS 13.080 Descriptors: SDIIS, quaky, so11 testing, chemical analysis. determlnatlon of content, nttrogen. volumetnc analys, Kjeldahl method. Pnce based on 4 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 03:24:13 MDTNo reproduction or networking permitted without license from IHS -,-,-