ISO 20279:2005

INTERNATIONAL ISO
STANDARD 20279
First edition
2005-07-01

Soil quality — Extraction of thallium and
determination by electrothermal atomic
absorption spectrometry
Qualité du sol — Extraction du thallium et dosage par spectrométrie
d'absorption atomique électrothermale




Reference number
ISO 20279:2005(E)
©
ISO 2005

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ISO 20279:2005(E)
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ISO 20279:2005(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Principle. 1
4 Reagents. 2
5 Apparatus . 3
6 Procedure . 4
6.1 Test portion . 4
6.2 Blank test solution. 4
6.3 Preparation of calibration solutions for thallium . 4
6.4 Calibration and determination, electrothermal atomic absorption spectrometry (ETAAS). 4
6.5 Direct measurement of calibration and test solutions, ETAAS . 5
7 Plotting the graph . 5
8 Calculation. 6
8.2 Calculation according to the method of standard additions. 6
8.3 Expression of results . 6
9 Interferences . 6
10 Precision. 7
11 Test report . 7
Bibliography . 8

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ISO 20279:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 20279 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
methods and soil characteristics.


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INTERNATIONAL STANDARD ISO 20279:2005(E)

Soil quality — Extraction of thallium and determination by
electrothermal atomic absorption spectrometry
WARNING — Thallium solutions are highly toxic. Appropriate measures shall be taken to avoid
ingestion. Care should be taken in the disposal of these solutions.
Certain procedures, reagents and apparatus used in this International Standard pose potential
hazards, especially in connection with concentrated acids, toxic solutions of thallium, and high-
pressure gases. Users should ensure that they are familiar with the safety procedures necessary in
such situations, and with any legal requirements (including waste disposal). If in any doubt, seek
advice from the competent authorities.
1 Scope
This International Standard specifies methods for extraction of thallium from soil by nitric acid and hydrogen
peroxide and its determination in the extract by electrothermal atomic absorption spectrometry (ETAAS).
NOTE The relevant working range of this method is approximately from 0,05 mg/kg to 100 mg/kg.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
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
ASTM E11:2004, Standard Specification for Wire Cloth and Sieves for Testing Purposes
3 Principle
Thallium is extracted from soil by a mixture of nitric acid and hydrogen peroxide, and determined in solution by
electrothermal atomic absorption spectrometry, in which discrete volumes of sample solution are dispensed
into a graphite tube. By increasing the temperature of this tube step by step, the processes of drying, thermal
decomposition of the matrix and thermal dissociation into free atoms occur. The resulting absorption signal
should (under optimum conditions) be a sharp symmetrical peak with a height proportional to the element
concentration in solution. See Table 1.
Table 1 — Measurement wavelength for thallium
Wavelength Spectral bandwidth
Element Measurement method
nm nm
Thallium 276,8 0,2 ETAAS
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ISO 20279:2005(E)
NOTE Thallium contents in non-polluted soils are low. Therefore, a highly sensitive analytical method like ETAAS is
necessary for the determination of trace concentrations. Unfortunately, severe interferences in aqua regia extracts of soils
are observed using ETAAS for thallium determination. Due to a high chloride concentration in aqua regia extracts, thallium
will be volatilised and lost during the pretreatment step. Therefore, in this International Standard, a mixture of nitric acid
and hydrogen peroxide will be used for the extraction of thallium from soil.
Aqua regia can be used with approximately the same extraction efficiency to extract thallium from soil.
However, for the determination of the element in the extract solution, other analytical methods, like inductively
coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry
(ICP-MS), shall be used.
4 Reagents
All reagents shall be of recognised analytical grade.
4.1 Water, demineralised or distilled, from an all-glass apparatus, conforming to Grade 2 of ISO 3696. The
water used for blank determinations, and for preparing reagents and standard solutions, shall have element
concentrations that are negligible compared with the lowest concentration to be determined in the sample
solutions.
4.2 Nitric acid, w(HNO ) = 65 %; ρ ~ 1,40 g/ml.
3
The same batch of nitric acid shall be used throughout the procedure.
4.3 Nitric acid, c(HNO ) = 0,5 mol/l.
3
Add 32 ml of nitric acid (4.2) to 500 ml of water in a 1 000 ml volumetric flask, fill to the mark with water and
mix well.
4.4 Hydrochloric acid, w(HCl) = 37 %; ρ ~ 1,185 g/ml.
The same batch of hydrochloric acid shall be used throughout the procedure.
4.5 Hydrogen peroxide, w(H O ) = 30 %.
2 2
The same batch of hydrogen peroxide solution shall be used throughout the procedure.
4.6 Palladium/magnesium nitrate modifier solution.
Dissolve 0,3 g of palladium nitrate [Pd(NO ) ] and 0,36 g of magnesium nitrate [Mg(NO ) ⋅6 H O] in a 100 ml
3 2 3 2 2
volumetric flask, fill to the mark with 0,5 mol/l nitric acid (4.3) and mix.
Alternatively, prepare the palladium/magnesium nitrate modifier solution as follows. Dissolve 0,14 g of
palladium powder in a 250 ml beaker with 3,5 ml of nitric acid (4.2), add 10 µl of hydrochloric acid (4.4),
evaporate the solution to near dryness on a water bath or hot-plate, then add 0,36 g of magnesium nitrate
[Mg(NO ) ⋅⋅⋅⋅6 H O]. Dissolve this solid residue in 50 ml of nitric acid (4.3), transfer the solution into a 100 ml
3 2 2
volumetric flask, fill to the mark with nitric acid (4.3) and mix. 10 µl of this solution are equal to 14 µg of Pd and
36 µg of Mg(NO ) .
3 2
4.7 Preparation of stock and standard solutions of individual elements.
Two sources of stock solutions are available:
 commercially available stock solutions;
 stock solutions prepared in the laboratory from pure elements or stoichiometrically defined salts or oxides.
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ISO 20279:2005(E)
NOTE Commercially available stock solutions have the advantage that they remove the need to handle toxic metals,
especially thallium, directly. However, special care needs to be taken to ensure that these solutions are supplied with a
certified composition from a reputable source and are checked on a regular basis.
4.8 Thallium stock solution, corresponding to ρ (Tl) = 1 000 mg/l.
4.9 Thallium standard solution, corresponding to ρ (Tl) = 100 mg/l.
Pipette 50,00 ml of the thallium stock solution (4.8) into a 500 ml volumetric flask, add 5 ml of nitric acid (4.2),
fill to the mark with water and mix well.
4.10 Thallium standard solution, corresponding to ρ (Tl) = 1 mg/l.
Pipette 1,00 ml of the thallium standard solution (4.9) into a 100 ml volumetric flask, add 2 ml of nitric acid
(4.2), fill to the mark with water and mix well. Prepare this solution on the day of use.
4.11 Blank calibration solution.
Dilute 5 ml of nitric acid (4.2) in a 100 ml volumetric flask and fill to the mark with water.
Cleaning of glassware: All glassware used in the determination of small amounts of this element shall be
cleaned carefully before use, e.g. by immersion in aqueous nitric acid solution, w(HNO ) = 5 %, for a minimum
3
of 6 h, followed by rinsing with water before use. The nitric acid shall be replaced each week. It can be helpful
to keep a separate set
...