INTERNATIONAL ISO

STANDARD 11261
First edition
1995-03-01

Soil quality - Determination of total

nitrogen - Modified Kjeldahl method

iTeh STANDARD PREVIEW

Quake du so/ - Dosage de Iazo te total - Methode de Kjeldahl modifiee
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ISO 11261:1995
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26445243a323/iso-11261-1995

Reference number
ISO 7 1261: 1995(E)
 Foreword
ISO (the International Organization for Standardization) is a worldwide
federation sf national Standards bodies (ISO member bodies). The work
of preparing International Standards is normally carried out through ISO
technical committees. Esch 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. ISO
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
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Standard requires approval by at least 75 % of the member bodies casting
a vote.

International Standard ISO

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11261 was prepared by Technical Committee
lSO/TC 190, Seil quality, Subcommittee SC 3, Chemical methods and seil
charac teris tics. ISO 11261:1995
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Annex A of this International Standard is for information only.
26445243a323/iso-11261-1995

0 ISO 1995
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronrc or mechanical, rncluding photocopyrng and
microfilm, without Permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-l 211 Geneve 20 l Switzerland
Printed in Switzerland

ii
INTERNATIONAL STANDARD 0 ISO ISO 11261:1995(E)

Soil quality - Determination of total nitrogen -

Modified Kjeldahl method

1 Scope 3 Principle

This International Standard specifies a method for the The method is based on the Kjeldahl-digestion, but
determination of the total nitrogen (ammonium-N, titanium dioxide (TiO,) is used as the catalyst instead
nitrate-N, nitrite-N and organic N) content of a soil. of selenium.
Nitrogen in N-N-linkages, N-0-linkages and some het-
NOTE 1 Titanium dioxide is ecotoxicologically less
erocyclics (especially pyridine) is only partially deter-
harmfull than selenium.
mined. This International Standard is applicable to all
types of soils. iTeh STANDARD PREVIEW
4 Reagents
(standards.iteh.ai)
All reagents shall be of recognized analytical grade.
ISO 11261:1995Use water of grade 2 complying with ISO 3696.
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26445243a323/iso-11261-1995
4.1 Salicylic acid/sulfuric acid.
2 Normative references
Dissolve 25 g of salicylic acid in 1 litre of concentrated
sulfuric acid Q = 1,84 g/cm3).
The following Standards contain provisions which, (
through reference in this text, constitute provisions
of this International Standard. At the time of publi- 4.2 Potassium sulfate catalyst mixture.
cation, the editions indicated were valid. All Standards
are subject to revision, and Parties to agreements Grind and thoroughly mix 200 g of potassium sulfate,
based on this International Standard are encouraged 6 g of copper(ll) sulfate pentahydrate and 6 g of
titanium dioxide, with the crystal structure of anatase.
to investigate the possibility of applying the most re-
cent editions of the Standards indicated below.
Members of IEC and ISO maintain registers of cur- 4.3 Sodium thiosulfate pentahydrate.
rently valid International Standards.
Crush the crystals to form a powder that Passes
ISO 3696: 1987, Water for analytical laboratory use - through a sieve with an aperture of 0,25 mm.
Specifica tion and tes t me thods.
4.4 Sodium hydroxide, c(NaOH) = 10 mol/l.
ISO 5725:1986, Precision of test methods - Deter-
mina tion of repeatability and reproducibility for a
4.5 Boric acid Solution, p(H,BO,) = 20 g/l.
Standard test method by inter-laboratory tests.

ISO 11464: 1994, Soil quality - Pretreatmen t of sam- 4.6 Mixed indicator.
ples for physico-Chemical analyses.
Dissolve 0,l g of bromocresol green and 0,02 g of
ISO 11465: 1993, Soil quality - Determination of dry methyl red in 100 ml of ethanol.
matter and water content on a mass basis -
Gravimetric method. 4.7 Sulfuric acid, c(H+) = 0,Ol mol/l.

7
ISO 11261:1995(E) 0 ISO

5 Apparatus under the condenser of the distillation apparatus in

such a way that the end of the condenser dips into
Usual laboratory equipment and 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
5.1 Digestion flasks or tubes, of nominal volume
condensate (the amount for quantitative results de-
50 ml, suitable for the digestion stand.
pends on the dimensions of the apparatus), rinse the
end of the condenser, add a few drops of indicator
5.2 Digestion stand. (4.6) to the distillate and titrate with sulfuric acid (4.7)
to a violet endpoint.
NOTE 2 Glass tubes placed in holes drilled into an alu-
minium block are also suitable. NOTE 5 A potentiometric titration is also possible. The
endpoint of the titration should be pH = 5,0.
5.3 Distillation apparatus, preferably of the
Parnas-Wagner type. 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.
5.4 Burette, graduated in intervals of 0,Ol ml or
smaller. Carry out a blank test in which the same procedure is
performed without soil. Notify the consumption of
6 Pretreatment of soil samples sulfuric acid in the blank test and in the tests of the
soil samples.
Samples shall be pretreated according to ISO 11464.

NOTE 3 Losses of nitrogen tan occur with samples of

high ammonium-N iTeh STANDARD
and nitrate-N content. Therefore, ex- PREVIEW
8 Calculation of the result
cessive drying (105 “C) should be avoided.
(standards.iteh.ai)
The total content of nitrogen, (wr,,), in milligrams per
gram, is calculated using the formula:
7 Procedure ISO 11261:1995
(VI - vo) x c(H+) x MN
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Place a test Portion of the air-dried soil Sample, of WN = X
26445243a323/iso-11261-1995 m 100
about 0,2 g (expected nitrogen content N 0,5 %) to
1 g (expected nitrogen content N 0,l %), in the di- where
gestion flask (5.1). Add 4 ml of salicylic/sulfuric acid
(4.1) and swirl the flask until the acid is thoroughly is the volume, in millilitres, of the sulfuric
mixed with the soil. Allow the mixture to stand for at acid (4.7) used in the titration of the
least several hours (or overnight). Add 0,5 g of sodium Sample [indicator (4.6)];
thiosulfate (4.3) through a dry funnel with a long stem
that reaches down into the bulb of the digestion flask, VO is the volume, in millilitres, of the sulfuric
and heat the mixture cautiously on the digestion stand acid (4.7) used in the blank test [indicator
(5.2) until frothing has ceased. (4.WJ;

Then cool the flask, add 1,l g of the catalyst mixture c(H+) is the concentration of H+ in the sulfuric
(4.2) and heat until the digestion mixture becomes acid (4.7) in moles per litre [e.g. if
clear. Boil the mixture gently for up to 5 h so that the 0,Ol mol/1 sulfuric acid is used,
sulfuric acid condenses about 1/3 of the way up to the c(H+) = 0,02 mol/l];
neck of the flask. Ensure that the temperature of the is the molar mass of nitrogen, in grams per
MN
Solution does not exceed 400 “C. mole (= 14);
NOTE 4 In most cases a boiling period of 2 h is sufficient. m is the mass, in grams, of the air-dried
Sample of soil;
After completion of the digestion Step, allow the flask
to cool and add about 20 ml of water slowly while wH,O is the water content, expressed as a per-
shaking. Then swirl the flask to bring any insoluble centage by mass, on the basis of oven-
material into Suspension and transfer the contents to dried soll, determined according to
the distillation apparatus (5.3). Rinse three times with ISO 11465.
water to complete the transfer. Add 5 ml of boric acid
(4.5) to a 100 m I conical flask and place the flask Round the result to two significant figures.

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0 ISO ISO 11261:1995(E)

9 Precision 10 Test report

The precision data according to ISO 5725 were de- The test report shall contain the following information:
termined from an experiment conducted in 1992 in-
volving 14 laboratories and 4 soil samples. The results a) a reference to this International Standard;
obtained are given in table 1.
b) a complete identification of the Sample;
From the data in table 1, it tan be concluded that the
differente between two separate determinations c) the results of the determination;
should not exceed 15 % of the measured total nitro-
gen content when the content is less than 2 mg/g, d) any details not specified in this International
and IO % of the measured total nitrogen content Standard or which are optional, as well as any
when the content is greater than 2 mg/g. factor which may have affected the results.

Table 1 - General average of nitrogen content, s,, Y, SR and R calculated after elimination of outliers

Nitrogen content, wN Repeatability conditions of soil Reproducibility conditions

Sample No.
w/g mag wlg
Sf r % R

1 0,98 0,06 0,17 0,27 0,76

0,12 0,33 0,58 1,62

2
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3,ll
STANDARD PREVIEW
3 6,70 0,19 0,54 1,07 3,00
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0,74
4 10,88 0,26 0,89 2,50

S, is the repeatability Standard deviation

ISO 11261:1995
sR is the reproducibility Standard deviation
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r is the repeatability value R is the reproducibility value
26445243a323/iso-11261-1995
ISO 11261:1995(E)

Annex A
(informative)

Bibliography

[1] THUN, HERRMANN and KNICKMANN, Die Untersuchung von Böden (1955), Neumann Verlag, Radebeul und
Berlin.

[2] PAGE, A.L. et al., Methods of soil analysis, Part 2 (1982). American Society of Agronomy and So;/ Science
of America, Madison, WI.

[3] WILLIAMS, P.C. J. SC;. Fd. Agric. 24 (1973), p. 343.

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ISO 11261:1995(E)

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ISO 11261:1995
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26445243a323/iso-11261-1995

ICS 13.080
Descriptors: soils, quality, soil testing, Chemical analysis, determlnatlon of content, nitrogen, volumetric analysis, Kjeldahl method.

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