SIST ISO 16590:2001
(Main)Water quality -- Determination of mercury -- Methods involving enrichment by amalgamation
Water quality -- Determination of mercury -- Methods involving enrichment by amalgamation
Qualité de l'eau -- Dosage du mercure -- Méthodes après enrichissement par amalgame
Kakovost vode - Določevanje živega srebra - Metoda z bogatenjem z amalganiranjem
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INTERNATIONAL ISO
STANDARD 16590
First edition
2000-12-15
Water quality — Determination of
mercury — Methods involving enrichment
by amalgamation
Qualité de l'eau — Dosage du mercure — Méthodes après enrichissement
par amalgame
Reference number
ISO 16590:2000(E)
©
ISO 2000
---------------------- Page: 1 ----------------------
ISO 16590:2000(E)
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ISO 16590:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative references .1
3 General interferences.2
4 Determination of mercury after tin(II) chloride reduction and enrichment by amalgamation .3
5 Determination of mercury after sodium tetrahydroborate reduction and enrichment by
amalgamation.10
6 Precision data .14
Annex A (informative) Ultrasonic digestion method .17
Annex B (informative) Autoclave digestion method.18
Annex C (informative) Microwave digestion method.19
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ISO 16590:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 16590 was prepared by Technical Committee ISO/TC 147, Water quality,
Subcommittee SC 2, Physical, chemical and biochemical methods.
Annexes A, B and C of this International Standard are for information only.
This International Standard is equivalent to EN 12338.
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INTERNATIONAL STANDARD ISO 16590:2000(E)
Water quality — Determination of mercury — Methods involving
enrichment by amalgamation
WARNING — Mercury and mercury compounds are very toxic. Extreme caution is recommended when
handling samples and solutions which contain or may contain mercury.
1 Scope
This International Standard specifies two methods for the determination of mercury, one using tin(II) chloride and
the other sodium tetrahydroborate as reducing agent. The methods are suitable for the determination of mercury in
water, for example in ground, surface or waste water, in the concentration range 0,01 �g/l to 1 �g/l. Higher
concentrations may be determined if the water sample is diluted.
The total mercury content of the water is determined after digestion of the sample. If only soluble mercury
compounds are to be determined, the sample is filtered through a 0,45 �m membrane filter prior to digestion.
Mono- or divalent mercury is reduced to the elemental form by a reducing agent such as tin(II) chloride, SnCl ,or
2
sodium tetrahydroborate, NaBH , in an acid medium. Elemental mercury is then stripped from the solution with the
4
aid of a stream of inert gas with negligible mercury content and transported over a noble-metal surface with a large
area, such as gold/platinum gauze, on which the mercury is adsorbed. The mercury is released by rapid heating of
the adsorbent and further transported in a stream of carrier gas to a suitable cuvette. Absorbances are measured at
a wavelength of 253,7 nm in the radiation beam of an atomic absorption spectrometer. Concentrations are
calculated using a calibration curve.
In order to fully decompose all of the mercury compounds, a digestion procedure is required. Digestion can be
omitted only if it is certain that the mercury concentration may be measured without this pretreatment.
Careful consideration should be given to whether, and to what extent, particular problems will require the
specification of additional conditions.
It is absolutely essential that analyses conducted in accordance with this International Standard are carried out by
suitably qualified staff.
In natural water sources, mercury compounds generally occur only in very small concentrations of less than
0,1 �g/l. Higher concentrations may be found, for example, in waste water. Both inorganic and organic compounds
of mercury can be present. Mercury may accumulate in sediment and sludge.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 5667-1:1980, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes.
ISO 5667-2:1991, Water quality — Sampling — Part 2: Guidance on sampling techniques.
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ISO 16590:2000(E)
ISO 5667-3:1994, Water quality — Sampling — Part 3: Guidance on the preservation and handling of samples.
3 General interferences
With mercury, there is a risk that exchange reactions, that is adsorption and desorption, will occur on the walls of
the reaction vessel. It is therefore essential that 4.6 is followed exactly.
Mercury vapour can diffuse through various plastics. Therefore, special consideration shall be given to the choice
of tubing material. Glass or special plastics tubing, e.g. FEP tubes, may be used (FEP = perfluoroethene-
hexafluoropropene copolymer). Silicone tubing, for example, is unsuitable.
Volatile organic substances can absorb in the UV range and be mistaken for mercury. They are in most cases
destroyed by adding potassium permanganate until the solution is permanently coloured red and removed by
purging for 10 min with an inert gas, prior to reduction of the mercury compounds. Often, such interference by non-
specific absorption can also be eliminated by using a background compensation system.
All solutions shall be brought to the same temperature (� 25 °C) before reduction and stripping of the mercury
vapour. Water condensation on the cuvette windows can be prevented by heating the cuvette with, for example, an
infrared lamp.
The interference which occurs due to the presence of other elements in the matrix depends on the choice of
reducing agent. Element concentrations in excess of those listed in Table 1 may cause too low results.
Less interference arises from heavy metals if tin(II) chloride is used rather than sodium tetrahydroborate. When
flow systems are used, interference effects due to heavy metals may be less than indicated in Table 1.
Tin(II) chloride causes such extensive contamination of the apparatus with tin that considerable interference occurs
if sodium tetrahydroborate is used afterwards. Separate systems are therefore used for reductions with tin(II)
chloride and with sodium tetrahydroborate.
Table 1 — Acceptable concentrations of some matrix elements in the test solution
Reducing agent NaBH NaBH SnCl
4 4 2
Medium 0,5 mol/l HCl 5 mol/l HCl � 0,2 g/l Fe(III) 0,5 mol/l HCl
Element Acceptable concentration (mg/l)
Cu(II) 10 10 500
Ni(II) 1 500 500
Ag(I) 0,1 10 1
–
I 100 10 0,1
As(V) 0,5 0,5 0,5
Bi(III) 0,05 0,5 0,5
Sb(III) 0,5 0,5 0,5
Se(IV) 0,005 0,05 0,05
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ISO 16590:2000(E)
4 Determination of mercury after tin(II) chloride reduction and enrichment by
amalgamation
4.1 Working range
The method is applicable to the determination of the mercury content in concentrations from 0,01 �g/l to 1 �g/l.
Higher concentrations may also be determined if the water sample is diluted.
NOTE Measurements in this concentration range require the use of highest-purity reagents and clean flasks, mercury-free
laboratory air and a very stable measurement system.
4.2 Principle
Mercury is reduced to the elemental form by tin(II) chloride and transported in a stream of inert gas with negligible
mercury content over a noble-metal surface with a large area, such as gold/platinum gauze, on which the mercury
is adsorbed.
The mercury is released by rapid heating of the adsorbent and further transported in a stream of carrier gas to the
absorption cell where the absorbance is measured at 253,7 nm.
4.3 Interferences
Seealsoclause3.
Iodide in concentrations of � 0,1 mg/l causes interference with the determination due to the formation of mercury
complexes. In this case, use another method such as reduction with sodium tetrahydroborate (see clause 5).
Because of the reduction potential of the tin(II) chloride solution, various inorganic mercury compounds, such as
mercury sulfide, and organic mercury compounds cannot be fully reduced without digestion.
4.4 Reagents
At least "analytical grade" reagents or those with the lowest possible mercury content shall be used. The mercury
content of the water and reagents shall be negligible compared to the lowest analyte concentration.
4.4.1 Water, double-distilled or of similar purity, for preparing solutions.
4.4.2 Nitric acid,� (HNO ) = 1,40 g/ml.
3
4.4.3 Sulfuric acid,� (H SO ) = 1,84 g/ml.
2 4
4.4.4 Hydrochloric acid,� (HCl) = 1,19 g/ml.
4.4.5 Potassium permanganate solution.
Dissolve 50 g of potassium permanganate, KMnO , in 1 000 ml of water.
4
4.4.6 Stabilizer solution.
Dissolve 5 g of potassium dichromate, K Cr O , in 500 ml of nitric acid (4.4.2) and dilute to 1 000 ml with water.
2 2 7
WARNING — Potassium dichromate is toxic. Caution should be exercised when handling the solid material
and its solutions.
4.4.7 Potassium peroxodisulfate solution.
Dissolve 40 g of potassium peroxodisulfate, K S O , in 1 000 ml of water.
2 2 8
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ISO 16590:2000(E)
4.4.8 Hydroxylamine chloride solution.
Dissolve 10 g of hydroxylamine chloride, H NOH�HCl, in 100 ml of water.
2
4.4.9 Tin(II) chloride solution.
Dissolve 5 g of tin(II) chloride dihydrate, SnCl ·2H O, in 30 ml of hydrochloric acid (4.4.4) and dilute to 100 ml with
2 2
water. A solution of lower concentration, e.g. 0,5 g in 100 ml, may be used with flow systems. Prepare this latter
solution freshly daily from the more concentrated solution by diluting with water.
If a high result for the blank is obtained, pass nitrogen through the solution for 30 min in order to remove traces of
mercury.
4.4.10 Mercury stock solution I,� (Hg) = 100 mg/l.
Dissolve 108,0 mg of mercury(II) oxide, HgO, in 10 ml of the stabilizer solution (4.4.6) and dilute to 1 000 ml with
water. 1 ml of this solution corresponds to 0,1 mg of mercury.
Stock solution I may be prepared from a commercially available mercury standard. The solution is stable for about
1 month.
4.4.11 Mercury stock solution II,� (Hg) = 1 mg/l.
Add 10 ml of stabilizer solution (4.4.6) to 10 ml of stock solution I (4.4.10) and dilute to 1 000 ml with water. 1 ml of
this solution corresponds to 1 �g of mercury. The solution is stable for about 1 week.
4.4.12 Mercury standard solution I,� (Hg) = 100 �g/l.
Add 10 ml of stabilizer solution (4.4.6) to 100 ml of stock solution II (4.4.11) and dilute to 1 000 ml with water. 1 ml
of this solution corresponds to 100 ng of mercury.
Prepare the solution on the day of use.
4.4.13 Mercury standard solution II,� (Hg) = 10 �g/l.
Dilute 1 ml of stabilizer solution (4.4.6) and 10 ml of standard solution I (4.4.12) to 100 ml with water. 1 ml of this
solution corresponds to 10 ng of mercury. The solution is stable for only a short time and shall be freshly prepared
before use.
4.4.14 Mercury standard solution III,� (Hg) = 1 �g/l.
Dilute 1 ml of stabilizer solution (4.4.6) and 10 ml of standard solution II (4.4.13) to 100 ml with water. 1 ml of this
solution corresponds to 1 ng of mercury. Prepare the solution freshly before each series of measurements.
4.4.15 Mercury calibration solutions.
Prepare calibration solutions appropriate to the volume and expected mercury concentrations of the test solutions.
For the concentration range from 0,01 �g/l to 0,1 �g/l, for example, proceed as follows:
� Pipette into each of six 100 ml volumetric flasks 1,0 ml, 2,0 ml, 4,0 ml, 6,0 ml, 8,0 ml and 10 ml respectively of
mercury standard solution III (4.4.14).
� Add 1 ml of stabilizer solution (4.4.6) to each.
� Fill each flask to the mark with water and mix thoroughly.
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ISO 16590:2000(E)
These calibration solutions contain 0,01 �g/l, 0,02 �g/l, 0,04 �g/l, 0,06 �g/l, 0,08 �g/l and 0,1 �g/l mercury
respectively. Prepare them freshly before each series of measurements.
For the concentration range from 0,1 �g/l to 1 �g/l, proceed in the same manner using mercury standard solution II
(4.4.13). In this case, the reference solutions contain 0,1 �g/l, 0,2 �g/l, 0,4 �g/l, 0,6 �g/l, 0,8 �g/l and 1 �g/l of
mercury respectively. If relatively large volumes of the test solution are used, increase the volumes of the reference
solutions and the amount of standard solution added accordingly. Prepare the solutions freshly before each series
of measurements.
If the calibration measurements are to be done in duplicate, prepare another set of solutions.
4.4.16 Reagent blank solution.
Prepare a volume of blank solution corresponding to that of the test solution by diluting 10 ml of stabilizer solution
(4.4.6) to 1 000 ml with water. Use the same digestion procedure as for the sample (see 4.7). The reagent blank
shall be included in each batch of analyses.
4.4.17 Gas-washing solution.
Dissolve 2,5 g of tin(II) chloride dihydrate, SnCl �2H O, with 7,5 ml of sulfuric acid (4.4.3) in a small amount of
2 2
water and dilute to 50 ml with water.
4.4.18 Washing solution for glassware.
Dilute 150 ml of nitric acid (4.4.2) to 1 000 ml with water.
4.5 Apparatus
Before use, wash all glassware thoroughly with dilute nitric acid (4.4.18) and then rinse thoroughly several times
with water.
4.5.1 Atomic absorption spectrometer (AAS), with an appropriate monitoring system. A background correction
system is recommended.
4.5.2 Radiation source, for the determination of mercury, e.g. a hollow-cathode or electrodeless discharge
lamp.
4.5.3 Mercury attachment with amalgam accessory, consisting of
� an absorption cell consisting of a glass or quartz tube, inner diameter about 2 cm, at least 15 cm long
(depending on the AAS instrument) and with quartz windows;
� an air-circulating pump (e.g. membrane pump, peristaltic pump), capacity 1 l/min to 2 l/min, with plastics tubing
(closed system);
� a cylinder, with a pressure-reducing valve, of inert gas (e.g. nitrogen or argon) with a negligible mercury
content;
� a flow meter with plastics tubing (see clause 3);
� a reaction vessel consisting of, for example, a 100 ml, 250 ml or 1 000 ml flat-bottomed flask as shown in
Figure 1, with a ground-glass stopper and wash bottle insert with glass frit, porosity 1;
� a heating source for the absorption cell, with sufficient heating capacity to prevent condensation of water (the
temperature of the absorption cell shall remain the same throughout the analysis);
� a quartz tube with a heating element and noble-metal adsorbent (such as gold/platinum gauze);
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ISO 16590:2000(E)
� a 100 ml gas-washing flask with a flashback prevention valve;
� a three-way stopcock.
An example of a closed system is shown in Figure 1.
NOTE Caution should be used with regard to the choice of plastics material for pumps and tubing (see clause 3). A
continuous-flow or flow-injection system is permissible. It is recommended that the user follow the instructions given by the
manufacturer.
Key
1 Air-circulating pump, capacity 1 l/min to 2 l/min
2 Flow meter
3 Three-way stopcock
4 Absorption cell: internal diameter 2 cm; length 15 cm
5 Au-Pt gauze
6 Flashback prevention valve
7 Ground-glass stopper
8 Reaction flask, 100 ml, 250 ml or 1 000 ml
9SnCl in H SO
2 2 4
10 Inert gas
11 Heating device
Figure 1 — Attachment apparatus for the determination of mercury after tin(II) chloride reduction
and enrichment by amalgamation (closed system)
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ISO 16590:2000(E)
4.6 Sampling and sample pretreatment
In sampling and sample pretreatment, the requirements in ISO 5667-1, ISO 5667-2 and ISO 5667-3 shall be taken
into account.
Suitable materials for sampling vessels shall be used: these are borosilicate glass, quartz, polysulfone (PSF) and
perfluoroethene-hexafluoropropene copolymer (FEP).
Make sure that the sampling vessel contains no mercury and causes no losses of mercury by adsorption.
In order to limit the losses by, for example, adsorption on the vessel walls, add 10 ml of stabilizer solution (4.4.6)
and make up to 1 000 ml with the sample.
The sample shall have a pH of approximately 1 and shall show a yellow-orange colour indicating an excess of
dichromate.
If these conditions are not met, add additional stabilizer, and include the appropriate volume correction factor in the
calculations.
4.7 Digestion method using permanganate and peroxodisulfate
The wet-chemical digestion procedure as described hereafter should preferably be carried out. Alternatively, one of
the digestion methods given in annexes A to C may be used. In the latter case, however, the efficiency of the
method compared to the wet-digestion method shall be checked.
Transfer 100 ml of the stabilized water sample (see 4.6) or an appropriate volume (maximum 1 000 ml) of sample
to a flask made from one of the materials mentioned in 4.6.
Carefully add 15 ml of potassium permanganate solution (4.4.5), 1 ml of nitric acid (4.4.2) and 1 ml of sulfuric acid
(4.4.3).
Shake the mixture well after each addition.
Allow the solution to stand for 15 min, then add 10 ml of potassium peroxodisulfate solution (4.4.7).
Place the loosely stoppered flask on a heating block or water bath at 95 °Cfor 2h.
During the digestion, ensure that there is an excess of potassium permanganate. If this is not the case, increase
the amount of potassium permanganate added or start with a smaller volume of sample.
Allow the solution to cool to room temperature.
If different sample volumes, and accordingly different reagent volumes, have been used, dilute the digests to a
specific volume.
Analyse the digests as soon as possible.
Prepare a reagent blank solution in the same manner (4.4.16), using the corresponding volume of water (4.4.1)
with stabilizer solution (4.4.6) instead of the water sample.
The permanganate can cause blank problems. In this case, reduce the permanganate concentration, provided the
content of organic matter is low, or use a different digestion method (see annexes A to C).
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ISO 16590:2000(E)
4.8 Procedure
4.8.1 Preparation for determination
Before beginning the measurement procedure, set the instrument parameters in accordance with the
manufacturer's instructions and align the absorption cell.
If the digest was prepared in accordance with the instructions in 4.7, immediately before measurement add to the
entire digestion solution 5 ml (or more, if required) of hydroxylamine chloride solution (4.4.8). The 5 ml of
hydroxylamine chloride solution are generally sufficient for reducing excess oxidizing agents and for dissolving the
precipitated manganese dioxide. If the solution has not cleared after 30 min, make another addition of
hydroxylamine chloride.
If an aliquot of the sample is taken for analysis, the sample solution shall first be made up to a specific volume, e.g.
200 ml.
Transfer the test solution (digest or aliquot) to the reaction vessel and connect to the analytical apparatus.
To 100 ml of test solution (or less), add 2 ml of tin(II) chloride solution (4.4.9).
If the reducing agent has to be added manually, connect the reaction vessel to the apparatus immediately after the
addition of the tin(II) chloride solution.
For larger volumes of test solution (up to 1 000 ml), increase the volume of reducing agent up to a maximum of
5ml.
In a closed system with an air-circulating pump, pass inert gas at a rate of 1 l/min to 2 l/min through the reaction
vessel and noble-metal adsorbent. When adsorption is complete, turn off the pump and open the three-way
stopcock.
In an open system, strip the water sample in an inert-gas stream with a negligible mercury content.
Release the adsorbed mercury by rapid heating of the adsorbent to at least 600 °C.
Transport the mercury vapour in an inert-gas stream, flowing at e.g. 75 ml/min, which shall not pass through the
test solution, into the absorption cell and measure the peak height or, preferably, the peak area.
Measure the absorbances of the calibration solutions (4.4.15) and the reagent blank (4.4.16) in the same manner
as the water sample.
4.8.2 Analysis using the method of standard calibration
For the analysis, prepare a calibration curve as follows:
Prepare the mercury calibration solutions as described in 4.4.15.
Measure the absorbances of the calibration and blank solutions as described in 4.8.
From the series of results obtained, determine the equation corresponding to the linear calibration line.
4.8.3 Analysis using the standard additions method of calibration
If the method of standard calibration does not yield sufficiently accurate results, e.g. because of matrix effects, the
standard additions method shall be used, provided no additive errors occur and that the absorbances of the spiked
water samples lie in the linear working range, i.e. the results are in the linear region of the calibration curve. The
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ISO 16590:2000(E)
concentration of added mercury shall correspond to the expected mercury content of the sample. As an example,
for a sample volume of 50 ml and an expected mercury concentration of 0,1 �g/l, proceed as follows:
Into each of four 100 ml reaction flasks, place 50 ml of the test solution (see 4.8.1).
To three of the flasks, add 0,5 ml, 1,0 ml or 1,5 ml respectively of mercury standard solution II (4.4.13). The spikes
correspond to 0,1 �g/l, 0,2 �g/l and 0,3 �g/l of mercury respectively.
Measure the mercury concentration of the contents of all four flasks in accordance with the instructions in 4.8.
With the reagent blank solution (4.4.16), follow the same procedure as used for the test solution.
4.9 Calculation
4.9.1 Calculation using the calibration curve
Calculate the concentration of mercury using the following equation:
()A��AV
0m
� �
bV�
p
where
� is the concentration of mercury in the sample, in micrograms per litre;
A is the absorbance or integrated absorbance of the water sample;
A is the absorbance or the integrated absorbance of the reagent blank solution;
0
b is the slope of the calibration curve (a measure of the sensitivity), in litres per microgram;
V is the volume of sample used to prepare the test solution, in millilitres;
p
V is the volume of the test solution, in millilitres.
m
4.9.2 Calculation using the standard additions method
Prepare a calibration line using the measured absorbances of the water sample and of the series of calibration
solutions including the sample (made by spiking the sample with standard solutions containing increasing quantities
of mercury).
Determine the mercury concentration of the test solution by extrapolating the calibration line to zero absorbance.
Determine the mercury concentration of the reagent blank solution in a similar manner and subtract it from the
value obtained for the test solution.
The mercury concentration may also be calculated using a linear-regression approach.
Any additional dilution steps will have to be allowed for in the calculation.
4.10 Expression of results
Report the results rounded to the nearest 0,01 �g/l.
EXAMPLE
Mercury (Hg) 0,04 �g/l;
Mercury (Hg) 0,20 �g/l.
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ISO 16590:2000(E)
4.11 Test report
The test report shall contain the following details:
a) a reference to this International Standard;
b) identification of the water sample analysed;
c) the result stated as specified in 4.10;
d) the sample pretreatment and digestion method used;
e) details of any deviations from the method specified and of any circumstances that may have affected the result;
f) the date of the analysis.
5 Determination of mercury after sodium tetrahydroborate reduction and enrichment by
amalgamation
5.1 Working range
The method is applicable to the determination of the mercury content in concentrations from 0,01 �g/l to 1 �g/l.
Higher concentrations can also be determined by appropriate dilution of the sample.
NOTE Measurements in this concentration range require the use of highest-purity reagents and clean flasks, mercury-free
laboratory air and a very stable measurement system.
5.2 Principle
Mercury is reduced to the elemental form by sodium tetrahydroborate and transported in a stream of inert gas,
together with the hydrogen released, over a noble metal surface with a large area, such as gold/platinum gauze, on
which the mercury is adsorbed. The mercury is released by rapid heating of the adsorbent and further transported
in a stream of carrier gas to the absorption cell where the absorbance is measured at 253,7 nm.
5.3 Interferences
Seealsoclause3.
Nickel in concentrations of > 1 mg/l and silver in concentrations of > 0,1 mg/l in the test solution interfere with the
determination of mercury. In the presence of 1:1 hydrochloric acid [500 ml of concentrated hydrochloric acid (4.4.4)
diluted to 1 000 ml with water] and an iron(III) solution, nickel at up to 500 mg/l and silver at up to 10 mg/l cause no
interference.
The noble-metal adsorbent shall be cooled to < 100 °C in order to avoid interference which may otherwise be
caused by elements such as As, Sb and Se which form volatile hydrides with sodium tetrahydroborate.
5.4 Reagents
In addition to those reagents described in 4.4 [except tin(II) chloride solution], the following are required:
5.4.1 Gas-washing solution I: sodium hydroxide solution.
Dissolve 10 g of NaOH in 100 ml of water.
5.4.2 Gas-washing solution II: water as described in 4.4.1.
10 © ISO 2000 – All
...
SLOVENSKI STANDARD
SIST ISO 16590:2001
01-december-2001
.DNRYRVWYRGH'RORþHYDQMHåLYHJDVUHEUD0HWRGD]ERJDWHQMHP]
DPDOJDQLUDQMHP
Water quality -- Determination of mercury -- Methods involving enrichment by
amalgamation
Qualité de l'eau -- Dosage du mercure -- Méthodes après enrichissement par amalgame
Ta slovenski standard je istoveten z: ISO 16590:2000
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
SIST ISO 16590:2001 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
INTERNATIONAL ISO
STANDARD 16590
First edition
2000-12-15
Water quality — Determination of
mercury — Methods involving enrichment
by amalgamation
Qualité de l'eau — Dosage du mercure — Méthodes après enrichissement
par amalgame
Reference number
ISO 16590:2000(E)
©
ISO 2000
---------------------- Page: 2 ----------------------
ISO 16590:2000(E)
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ii © ISO 2000 – All rights reserved
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ISO 16590:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative references .1
3 General interferences.2
4 Determination of mercury after tin(II) chloride reduction and enrichment by amalgamation .3
5 Determination of mercury after sodium tetrahydroborate reduction and enrichment by
amalgamation.10
6 Precision data .14
Annex A (informative) Ultrasonic digestion method .17
Annex B (informative) Autoclave digestion method.18
Annex C (informative) Microwave digestion method.19
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ISO 16590:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 16590 was prepared by Technical Committee ISO/TC 147, Water quality,
Subcommittee SC 2, Physical, chemical and biochemical methods.
Annexes A, B and C of this International Standard are for information only.
This International Standard is equivalent to EN 12338.
iv © ISO 2000 – All rights reserved
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INTERNATIONAL STANDARD ISO 16590:2000(E)
Water quality — Determination of mercury — Methods involving
enrichment by amalgamation
WARNING — Mercury and mercury compounds are very toxic. Extreme caution is recommended when
handling samples and solutions which contain or may contain mercury.
1 Scope
This International Standard specifies two methods for the determination of mercury, one using tin(II) chloride and
the other sodium tetrahydroborate as reducing agent. The methods are suitable for the determination of mercury in
water, for example in ground, surface or waste water, in the concentration range 0,01 �g/l to 1 �g/l. Higher
concentrations may be determined if the water sample is diluted.
The total mercury content of the water is determined after digestion of the sample. If only soluble mercury
compounds are to be determined, the sample is filtered through a 0,45 �m membrane filter prior to digestion.
Mono- or divalent mercury is reduced to the elemental form by a reducing agent such as tin(II) chloride, SnCl ,or
2
sodium tetrahydroborate, NaBH , in an acid medium. Elemental mercury is then stripped from the solution with the
4
aid of a stream of inert gas with negligible mercury content and transported over a noble-metal surface with a large
area, such as gold/platinum gauze, on which the mercury is adsorbed. The mercury is released by rapid heating of
the adsorbent and further transported in a stream of carrier gas to a suitable cuvette. Absorbances are measured at
a wavelength of 253,7 nm in the radiation beam of an atomic absorption spectrometer. Concentrations are
calculated using a calibration curve.
In order to fully decompose all of the mercury compounds, a digestion procedure is required. Digestion can be
omitted only if it is certain that the mercury concentration may be measured without this pretreatment.
Careful consideration should be given to whether, and to what extent, particular problems will require the
specification of additional conditions.
It is absolutely essential that analyses conducted in accordance with this International Standard are carried out by
suitably qualified staff.
In natural water sources, mercury compounds generally occur only in very small concentrations of less than
0,1 �g/l. Higher concentrations may be found, for example, in waste water. Both inorganic and organic compounds
of mercury can be present. Mercury may accumulate in sediment and sludge.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 5667-1:1980, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes.
ISO 5667-2:1991, Water quality — Sampling — Part 2: Guidance on sampling techniques.
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ISO 16590:2000(E)
ISO 5667-3:1994, Water quality — Sampling — Part 3: Guidance on the preservation and handling of samples.
3 General interferences
With mercury, there is a risk that exchange reactions, that is adsorption and desorption, will occur on the walls of
the reaction vessel. It is therefore essential that 4.6 is followed exactly.
Mercury vapour can diffuse through various plastics. Therefore, special consideration shall be given to the choice
of tubing material. Glass or special plastics tubing, e.g. FEP tubes, may be used (FEP = perfluoroethene-
hexafluoropropene copolymer). Silicone tubing, for example, is unsuitable.
Volatile organic substances can absorb in the UV range and be mistaken for mercury. They are in most cases
destroyed by adding potassium permanganate until the solution is permanently coloured red and removed by
purging for 10 min with an inert gas, prior to reduction of the mercury compounds. Often, such interference by non-
specific absorption can also be eliminated by using a background compensation system.
All solutions shall be brought to the same temperature (� 25 °C) before reduction and stripping of the mercury
vapour. Water condensation on the cuvette windows can be prevented by heating the cuvette with, for example, an
infrared lamp.
The interference which occurs due to the presence of other elements in the matrix depends on the choice of
reducing agent. Element concentrations in excess of those listed in Table 1 may cause too low results.
Less interference arises from heavy metals if tin(II) chloride is used rather than sodium tetrahydroborate. When
flow systems are used, interference effects due to heavy metals may be less than indicated in Table 1.
Tin(II) chloride causes such extensive contamination of the apparatus with tin that considerable interference occurs
if sodium tetrahydroborate is used afterwards. Separate systems are therefore used for reductions with tin(II)
chloride and with sodium tetrahydroborate.
Table 1 — Acceptable concentrations of some matrix elements in the test solution
Reducing agent NaBH NaBH SnCl
4 4 2
Medium 0,5 mol/l HCl 5 mol/l HCl � 0,2 g/l Fe(III) 0,5 mol/l HCl
Element Acceptable concentration (mg/l)
Cu(II) 10 10 500
Ni(II) 1 500 500
Ag(I) 0,1 10 1
–
I 100 10 0,1
As(V) 0,5 0,5 0,5
Bi(III) 0,05 0,5 0,5
Sb(III) 0,5 0,5 0,5
Se(IV) 0,005 0,05 0,05
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ISO 16590:2000(E)
4 Determination of mercury after tin(II) chloride reduction and enrichment by
amalgamation
4.1 Working range
The method is applicable to the determination of the mercury content in concentrations from 0,01 �g/l to 1 �g/l.
Higher concentrations may also be determined if the water sample is diluted.
NOTE Measurements in this concentration range require the use of highest-purity reagents and clean flasks, mercury-free
laboratory air and a very stable measurement system.
4.2 Principle
Mercury is reduced to the elemental form by tin(II) chloride and transported in a stream of inert gas with negligible
mercury content over a noble-metal surface with a large area, such as gold/platinum gauze, on which the mercury
is adsorbed.
The mercury is released by rapid heating of the adsorbent and further transported in a stream of carrier gas to the
absorption cell where the absorbance is measured at 253,7 nm.
4.3 Interferences
Seealsoclause3.
Iodide in concentrations of � 0,1 mg/l causes interference with the determination due to the formation of mercury
complexes. In this case, use another method such as reduction with sodium tetrahydroborate (see clause 5).
Because of the reduction potential of the tin(II) chloride solution, various inorganic mercury compounds, such as
mercury sulfide, and organic mercury compounds cannot be fully reduced without digestion.
4.4 Reagents
At least "analytical grade" reagents or those with the lowest possible mercury content shall be used. The mercury
content of the water and reagents shall be negligible compared to the lowest analyte concentration.
4.4.1 Water, double-distilled or of similar purity, for preparing solutions.
4.4.2 Nitric acid,� (HNO ) = 1,40 g/ml.
3
4.4.3 Sulfuric acid,� (H SO ) = 1,84 g/ml.
2 4
4.4.4 Hydrochloric acid,� (HCl) = 1,19 g/ml.
4.4.5 Potassium permanganate solution.
Dissolve 50 g of potassium permanganate, KMnO , in 1 000 ml of water.
4
4.4.6 Stabilizer solution.
Dissolve 5 g of potassium dichromate, K Cr O , in 500 ml of nitric acid (4.4.2) and dilute to 1 000 ml with water.
2 2 7
WARNING — Potassium dichromate is toxic. Caution should be exercised when handling the solid material
and its solutions.
4.4.7 Potassium peroxodisulfate solution.
Dissolve 40 g of potassium peroxodisulfate, K S O , in 1 000 ml of water.
2 2 8
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ISO 16590:2000(E)
4.4.8 Hydroxylamine chloride solution.
Dissolve 10 g of hydroxylamine chloride, H NOH�HCl, in 100 ml of water.
2
4.4.9 Tin(II) chloride solution.
Dissolve 5 g of tin(II) chloride dihydrate, SnCl ·2H O, in 30 ml of hydrochloric acid (4.4.4) and dilute to 100 ml with
2 2
water. A solution of lower concentration, e.g. 0,5 g in 100 ml, may be used with flow systems. Prepare this latter
solution freshly daily from the more concentrated solution by diluting with water.
If a high result for the blank is obtained, pass nitrogen through the solution for 30 min in order to remove traces of
mercury.
4.4.10 Mercury stock solution I,� (Hg) = 100 mg/l.
Dissolve 108,0 mg of mercury(II) oxide, HgO, in 10 ml of the stabilizer solution (4.4.6) and dilute to 1 000 ml with
water. 1 ml of this solution corresponds to 0,1 mg of mercury.
Stock solution I may be prepared from a commercially available mercury standard. The solution is stable for about
1 month.
4.4.11 Mercury stock solution II,� (Hg) = 1 mg/l.
Add 10 ml of stabilizer solution (4.4.6) to 10 ml of stock solution I (4.4.10) and dilute to 1 000 ml with water. 1 ml of
this solution corresponds to 1 �g of mercury. The solution is stable for about 1 week.
4.4.12 Mercury standard solution I,� (Hg) = 100 �g/l.
Add 10 ml of stabilizer solution (4.4.6) to 100 ml of stock solution II (4.4.11) and dilute to 1 000 ml with water. 1 ml
of this solution corresponds to 100 ng of mercury.
Prepare the solution on the day of use.
4.4.13 Mercury standard solution II,� (Hg) = 10 �g/l.
Dilute 1 ml of stabilizer solution (4.4.6) and 10 ml of standard solution I (4.4.12) to 100 ml with water. 1 ml of this
solution corresponds to 10 ng of mercury. The solution is stable for only a short time and shall be freshly prepared
before use.
4.4.14 Mercury standard solution III,� (Hg) = 1 �g/l.
Dilute 1 ml of stabilizer solution (4.4.6) and 10 ml of standard solution II (4.4.13) to 100 ml with water. 1 ml of this
solution corresponds to 1 ng of mercury. Prepare the solution freshly before each series of measurements.
4.4.15 Mercury calibration solutions.
Prepare calibration solutions appropriate to the volume and expected mercury concentrations of the test solutions.
For the concentration range from 0,01 �g/l to 0,1 �g/l, for example, proceed as follows:
� Pipette into each of six 100 ml volumetric flasks 1,0 ml, 2,0 ml, 4,0 ml, 6,0 ml, 8,0 ml and 10 ml respectively of
mercury standard solution III (4.4.14).
� Add 1 ml of stabilizer solution (4.4.6) to each.
� Fill each flask to the mark with water and mix thoroughly.
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ISO 16590:2000(E)
These calibration solutions contain 0,01 �g/l, 0,02 �g/l, 0,04 �g/l, 0,06 �g/l, 0,08 �g/l and 0,1 �g/l mercury
respectively. Prepare them freshly before each series of measurements.
For the concentration range from 0,1 �g/l to 1 �g/l, proceed in the same manner using mercury standard solution II
(4.4.13). In this case, the reference solutions contain 0,1 �g/l, 0,2 �g/l, 0,4 �g/l, 0,6 �g/l, 0,8 �g/l and 1 �g/l of
mercury respectively. If relatively large volumes of the test solution are used, increase the volumes of the reference
solutions and the amount of standard solution added accordingly. Prepare the solutions freshly before each series
of measurements.
If the calibration measurements are to be done in duplicate, prepare another set of solutions.
4.4.16 Reagent blank solution.
Prepare a volume of blank solution corresponding to that of the test solution by diluting 10 ml of stabilizer solution
(4.4.6) to 1 000 ml with water. Use the same digestion procedure as for the sample (see 4.7). The reagent blank
shall be included in each batch of analyses.
4.4.17 Gas-washing solution.
Dissolve 2,5 g of tin(II) chloride dihydrate, SnCl �2H O, with 7,5 ml of sulfuric acid (4.4.3) in a small amount of
2 2
water and dilute to 50 ml with water.
4.4.18 Washing solution for glassware.
Dilute 150 ml of nitric acid (4.4.2) to 1 000 ml with water.
4.5 Apparatus
Before use, wash all glassware thoroughly with dilute nitric acid (4.4.18) and then rinse thoroughly several times
with water.
4.5.1 Atomic absorption spectrometer (AAS), with an appropriate monitoring system. A background correction
system is recommended.
4.5.2 Radiation source, for the determination of mercury, e.g. a hollow-cathode or electrodeless discharge
lamp.
4.5.3 Mercury attachment with amalgam accessory, consisting of
� an absorption cell consisting of a glass or quartz tube, inner diameter about 2 cm, at least 15 cm long
(depending on the AAS instrument) and with quartz windows;
� an air-circulating pump (e.g. membrane pump, peristaltic pump), capacity 1 l/min to 2 l/min, with plastics tubing
(closed system);
� a cylinder, with a pressure-reducing valve, of inert gas (e.g. nitrogen or argon) with a negligible mercury
content;
� a flow meter with plastics tubing (see clause 3);
� a reaction vessel consisting of, for example, a 100 ml, 250 ml or 1 000 ml flat-bottomed flask as shown in
Figure 1, with a ground-glass stopper and wash bottle insert with glass frit, porosity 1;
� a heating source for the absorption cell, with sufficient heating capacity to prevent condensation of water (the
temperature of the absorption cell shall remain the same throughout the analysis);
� a quartz tube with a heating element and noble-metal adsorbent (such as gold/platinum gauze);
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ISO 16590:2000(E)
� a 100 ml gas-washing flask with a flashback prevention valve;
� a three-way stopcock.
An example of a closed system is shown in Figure 1.
NOTE Caution should be used with regard to the choice of plastics material for pumps and tubing (see clause 3). A
continuous-flow or flow-injection system is permissible. It is recommended that the user follow the instructions given by the
manufacturer.
Key
1 Air-circulating pump, capacity 1 l/min to 2 l/min
2 Flow meter
3 Three-way stopcock
4 Absorption cell: internal diameter 2 cm; length 15 cm
5 Au-Pt gauze
6 Flashback prevention valve
7 Ground-glass stopper
8 Reaction flask, 100 ml, 250 ml or 1 000 ml
9SnCl in H SO
2 2 4
10 Inert gas
11 Heating device
Figure 1 — Attachment apparatus for the determination of mercury after tin(II) chloride reduction
and enrichment by amalgamation (closed system)
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ISO 16590:2000(E)
4.6 Sampling and sample pretreatment
In sampling and sample pretreatment, the requirements in ISO 5667-1, ISO 5667-2 and ISO 5667-3 shall be taken
into account.
Suitable materials for sampling vessels shall be used: these are borosilicate glass, quartz, polysulfone (PSF) and
perfluoroethene-hexafluoropropene copolymer (FEP).
Make sure that the sampling vessel contains no mercury and causes no losses of mercury by adsorption.
In order to limit the losses by, for example, adsorption on the vessel walls, add 10 ml of stabilizer solution (4.4.6)
and make up to 1 000 ml with the sample.
The sample shall have a pH of approximately 1 and shall show a yellow-orange colour indicating an excess of
dichromate.
If these conditions are not met, add additional stabilizer, and include the appropriate volume correction factor in the
calculations.
4.7 Digestion method using permanganate and peroxodisulfate
The wet-chemical digestion procedure as described hereafter should preferably be carried out. Alternatively, one of
the digestion methods given in annexes A to C may be used. In the latter case, however, the efficiency of the
method compared to the wet-digestion method shall be checked.
Transfer 100 ml of the stabilized water sample (see 4.6) or an appropriate volume (maximum 1 000 ml) of sample
to a flask made from one of the materials mentioned in 4.6.
Carefully add 15 ml of potassium permanganate solution (4.4.5), 1 ml of nitric acid (4.4.2) and 1 ml of sulfuric acid
(4.4.3).
Shake the mixture well after each addition.
Allow the solution to stand for 15 min, then add 10 ml of potassium peroxodisulfate solution (4.4.7).
Place the loosely stoppered flask on a heating block or water bath at 95 °Cfor 2h.
During the digestion, ensure that there is an excess of potassium permanganate. If this is not the case, increase
the amount of potassium permanganate added or start with a smaller volume of sample.
Allow the solution to cool to room temperature.
If different sample volumes, and accordingly different reagent volumes, have been used, dilute the digests to a
specific volume.
Analyse the digests as soon as possible.
Prepare a reagent blank solution in the same manner (4.4.16), using the corresponding volume of water (4.4.1)
with stabilizer solution (4.4.6) instead of the water sample.
The permanganate can cause blank problems. In this case, reduce the permanganate concentration, provided the
content of organic matter is low, or use a different digestion method (see annexes A to C).
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ISO 16590:2000(E)
4.8 Procedure
4.8.1 Preparation for determination
Before beginning the measurement procedure, set the instrument parameters in accordance with the
manufacturer's instructions and align the absorption cell.
If the digest was prepared in accordance with the instructions in 4.7, immediately before measurement add to the
entire digestion solution 5 ml (or more, if required) of hydroxylamine chloride solution (4.4.8). The 5 ml of
hydroxylamine chloride solution are generally sufficient for reducing excess oxidizing agents and for dissolving the
precipitated manganese dioxide. If the solution has not cleared after 30 min, make another addition of
hydroxylamine chloride.
If an aliquot of the sample is taken for analysis, the sample solution shall first be made up to a specific volume, e.g.
200 ml.
Transfer the test solution (digest or aliquot) to the reaction vessel and connect to the analytical apparatus.
To 100 ml of test solution (or less), add 2 ml of tin(II) chloride solution (4.4.9).
If the reducing agent has to be added manually, connect the reaction vessel to the apparatus immediately after the
addition of the tin(II) chloride solution.
For larger volumes of test solution (up to 1 000 ml), increase the volume of reducing agent up to a maximum of
5ml.
In a closed system with an air-circulating pump, pass inert gas at a rate of 1 l/min to 2 l/min through the reaction
vessel and noble-metal adsorbent. When adsorption is complete, turn off the pump and open the three-way
stopcock.
In an open system, strip the water sample in an inert-gas stream with a negligible mercury content.
Release the adsorbed mercury by rapid heating of the adsorbent to at least 600 °C.
Transport the mercury vapour in an inert-gas stream, flowing at e.g. 75 ml/min, which shall not pass through the
test solution, into the absorption cell and measure the peak height or, preferably, the peak area.
Measure the absorbances of the calibration solutions (4.4.15) and the reagent blank (4.4.16) in the same manner
as the water sample.
4.8.2 Analysis using the method of standard calibration
For the analysis, prepare a calibration curve as follows:
Prepare the mercury calibration solutions as described in 4.4.15.
Measure the absorbances of the calibration and blank solutions as described in 4.8.
From the series of results obtained, determine the equation corresponding to the linear calibration line.
4.8.3 Analysis using the standard additions method of calibration
If the method of standard calibration does not yield sufficiently accurate results, e.g. because of matrix effects, the
standard additions method shall be used, provided no additive errors occur and that the absorbances of the spiked
water samples lie in the linear working range, i.e. the results are in the linear region of the calibration curve. The
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ISO 16590:2000(E)
concentration of added mercury shall correspond to the expected mercury content of the sample. As an example,
for a sample volume of 50 ml and an expected mercury concentration of 0,1 �g/l, proceed as follows:
Into each of four 100 ml reaction flasks, place 50 ml of the test solution (see 4.8.1).
To three of the flasks, add 0,5 ml, 1,0 ml or 1,5 ml respectively of mercury standard solution II (4.4.13). The spikes
correspond to 0,1 �g/l, 0,2 �g/l and 0,3 �g/l of mercury respectively.
Measure the mercury concentration of the contents of all four flasks in accordance with the instructions in 4.8.
With the reagent blank solution (4.4.16), follow the same procedure as used for the test solution.
4.9 Calculation
4.9.1 Calculation using the calibration curve
Calculate the concentration of mercury using the following equation:
()A��AV
0m
� �
bV�
p
where
� is the concentration of mercury in the sample, in micrograms per litre;
A is the absorbance or integrated absorbance of the water sample;
A is the absorbance or the integrated absorbance of the reagent blank solution;
0
b is the slope of the calibration curve (a measure of the sensitivity), in litres per microgram;
V is the volume of sample used to prepare the test solution, in millilitres;
p
V is the volume of the test solution, in millilitres.
m
4.9.2 Calculation using the standard additions method
Prepare a calibration line using the measured absorbances of the water sample and of the series of calibration
solutions including the sample (made by spiking the sample with standard solutions containing increasing quantities
of mercury).
Determine the mercury concentration of the test solution by extrapolating the calibration line to zero absorbance.
Determine the mercury concentration of the reagent blank solution in a similar manner and subtract it from the
value obtained for the test solution.
The mercury concentration may also be calculated using a linear-regression approach.
Any additional dilution steps will have to be allowed for in the calculation.
4.10 Expression of results
Report the results rounded to the nearest 0,01 �g/l.
EXAMPLE
Mercury (Hg) 0,04 �g/l;
Mercury (Hg) 0,20 �g/l.
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ISO 16590:2000(E)
4.11 Test report
The test report shall contain the following details:
a) a reference to this International Standard;
b) identification of the water sample analysed;
c) the result stated as specified in 4.10;
d) the sample pretreatment and digestion method used;
e) details of any deviations from the method specified and of any circumstances that may have affected the result;
f) the date of the analysis.
5 Determination of mercury after sodium tetrahydroborate reduction and enrichment by
amalgamation
5.1 Working range
The method is applicable to the determination of the mercury content in concentrations from 0,01 �g/l to 1 �g/l.
Higher concentrations can also be determined by appropriate dilution of the sample.
NOTE Measurements in this concentration range require the use of highest-purity reagents and clean flasks, mercury-free
laboratory air and a very stable measurement system.
5.2 Principle
Mercury is reduced to the elemental form by sodium tetrahydroborate and transported in a stream of inert gas,
together with the hydrogen released, over a noble metal surface with a large area, such as gold/platinum gauze, on
which the mercury is adsorbed. The mercury is released by rapid heating of the adsorbent and further transported
in a stream of carrier gas to the absorption cell where the absorbance is measured at 253,7 nm.
5.3 Interferences
Seealsoclause3.
Nickel in concentrations of > 1 mg/l and silver in concentrations of > 0,1 mg/l in the test solution interfere with the
determination of mercury. In the presence of 1:1 hydrochloric acid [500 ml of concentra
...
NORME ISO
INTERNATIONALE 16590
Première édition
2000-12-15
Qualité de l'eau — Dosage du mercure —
Méthodes après enrichissement par
amalgame
Water quality — Determination of mercury — Methods involving
enrichment by amalgamation
Numéro de référence
ISO 16590:2000(F)
©
ISO 2000
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ISO 16590:2000(F)
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Imprimé en Suisse
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ISO 16590:2000(F)
Sommaire Page
Avant-propos.iv
1 Domaine d'application.1
2Références normatives .2
3Interférences générales .2
4 Dosage du mercure aprèsréduction avec le chlorure d'étain (II) et enrichissement par
amalgame .3
5 Dosage du mercure aprèsréduction avec le tétrahydroborate de sodium et enrichissement par
amalgame .11
6 Données de fidélité.15
Annexe A (informative) Méthode de digestion par ultrasons .18
Annexe B (informative) Méthode de digestion utilisant un autoclave.19
Annexe C (informative) Méthode de digestion par micro-ondes.20
Bibliographie .22
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ISO 16590:2000(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiéeaux
comités techniques de l'ISO. Chaque comité membre intéressé par une étude aledroit de faire partie ducomité
technique créé à cet effet. Les organisations internationales, gouvernementales et non gouvernementales, en
liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec la Commission
électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 3.
Les projets de Normes internationales adoptés par les comités techniques sont soumis aux comités membres pour
vote. Leur publication comme Normes internationales requiert l'approbation de 75 % au moins des comités
membres votants.
L’attention est appelée sur le fait que certains des éléments de la présente Norme internationale peuvent faire
l’objet de droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de
ne pas avoir identifié de tels droits de propriété et averti de leur existence.
La Norme internationale ISO 16590 a étéélaboréepar le comité technique ISO/TC 147, Qualité de l'eau,
sous-comité SC 2, Méthodes physiques, chimiques et biochimiques.
Les annexes A, B et C de la présente Norme Internationale sont données uniquement à titre d’information.
La présente Norme internationale est équivalente à l’EN 12338.
iv © ISO 2000 – Tous droits réservés
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NORME INTERNATIONALE ISO 16590:2000(F)
Qualité de l'eau — Dosage du mercure — Méthodes après
enrichissement par amalgame
AVERTISSEMENT — Le mercure et ses composés sont hautement toxiques. Des précautions extrêmes
sont recommandées lors de la manipulation des échantillons et des solutions contenant ou pouvant
contenir du mercure.
1 Domaine d'application
La présente Norme Internationale spécifie deux méthodes de dosage du mercure, faisant intervenir le
tétrahydroborate de sodium ou le chlorure d'étain (II) comme agent réducteur. Les méthodes conviennent pour le
dosage du mercure dans l'eau, par exemple dans les eaux souterraines, les eaux de surface et les eaux usées,
dans une gamme de concentrations allant de 0,01�g/l à 1�g/l. Des concentrations plus élevées peuvent être
déterminées par dilution de l'échantillon d'eau.
La teneur en mercure total de l'eau est déterminée après digestion de l'échantillon. Si le dosage porte uniquement
sur les composés solubles du mercure, une étape de filtration au moyen d'un filtre sur membrane de 0,45�mest
effectuée avant la digestion.
Le mercure monovalent ou divalent est réduit à la forme élémentaire par un agent réducteur tel que le chlorure
d'étain (II), SnCl ,ouletétrahydroborate de sodium, NaBH , en milieu acide. Le mercure élémentaire est ensuite
2 4
entraîné hors de la solution à l'aide d'un courant de gaz inerte ayant une teneur en mercure négligeable, puis
transporté sur une large surface en métal précieux, telle qu'une gaze or/platine, sur laquelle le mercure est
adsorbé. Le mercure est libéré par chauffage rapide du matériau adsorbant, puis transporté au moyen d'un courant
de gaz vecteur vers une cellule de mesurage appropriée. Les absorbances sont mesurées à la longueur d'onde de
253,7 nm dans le faisceau optique d'un spectromètre d'absorption atomique. Les concentrations sont calculées à
l'aide d'une courbe d'étalonnage.
Pour décomposer complètement tous les composés du mercure, il est nécessaire de procéder à une digestion.
Cette digestion ne peut être omise que s'il est certain que la concentration en mercure peut être mesurée sans ce
traitement préalable.
Il convient de rechercher si des problèmes particuliers nécessitent la spécification de conditions particulières
supplémentaires, et dans quelle mesure.
Il est absolument essentiel que les essais menés selon la présente Norme Internationale soient effectués par un
personnel convenablement qualifié.
Dans les sources d’eaux naturelles, les composés du mercure n'existent généralement qu'en très faibles
concentrations, inférieures à 0,1�g/l. Des concentrations plus élevées peuvent apparaître dans leseauxusées,
par exemple. Des composés à la fois organiques et inorganiques peuvent être présents. Le mercure peut
s'accumuler dans les sédiments et dans les boues.
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ISO 16590:2000(F)
2Références normatives
Les documents normatifs suivants contiennent des dispositions qui, par suite de la référence qui y est faite,
constituent des dispositions valables pour la présente Norme internationale. Pour les références datées, les
amendements ultérieurs ou les révisions de ces publications ne s’appliquent pas. Toutefois, les parties prenantes
aux accords fondés sur la présente Norme internationale sont invitées à rechercher la possibilité d'appliquer les
éditions les plus récentes des documents normatifs indiqués ci-après. Pour les références non datées, la dernière
édition du document normatif en référence s’applique. Les membres de l'ISO et de la CEI possèdent le registre des
Normes internationales en vigueur.
ISO 5667-1:1980, Qualité de l'eau—Échantillonnage — Partie 1: Guide général pour l'établissement des
programmes d'échantillonnage.
ISO 5667-2:1991, Qualité de l'eau—Échantillonnage — Partie 2: Guide général sur les techniques
d'échantillonnage.
ISO 5667-3:1994, Qualité de l'eau—Échantillonnage — Partie 3: Guide général pour la conservation et la
manipulation des échantillons.
3Interférences générales
Lors de l’analyse du mercure, le risque d'adsorption et de désorption sur les parois du récipient de réaction est
particulièrement important. Il est donc essentiel de suivre exactement la description donnéeen4.6.
Les vapeurs de mercure peuvent diffuser à travers différentes matières plastiques. Pour cette raison, l'attention est
attiréetoutparticulièrement sur le choix du matériau constitutif des tubes. Les tubes en verre ou en matière
plastique spéciale, par exemple les tubes en FEP (FEP: copolymère de perfluoroéthylène/haxafluoropropylène),
sont utilisables. Les tubes en silicone, par exemple, ne conviennent pas.
Les substances organiques volatiles peuvent absorber dans le domaine U.V. et être considérées à tort comme du
mercure. Ces substances sont, dans la plupart des cas, détruites par ajout de permanganate de potassium jusqu'à
l'obtention d'une coloration rouge constante de la solution, puis sont éliminées par aération pendant 10 min au
moyen d'un gaz inerte avant la réduction des composés du mercure. Souvent, cette interférence par absorption
non spécifique peut également être éliminée par un système de compensation de fond.
Toutes les solutions doivent être amenées à la même température (� 25 °C) avant la réduction et l'entraînement
des vapeurs de mercure. La condensation d'eau sur les fenêtres de la cellule de mesurage peut être évitéeen
chauffant cette dernière au moyen d'une lampe à infrarouge, par exemple.
Les interférences dues à la présence d'autres éléments dans la matrice dépendent du choix de l'agent réducteur.
Les concentrations en éléments supérieures aux valeurs mentionnées au Tableau 1 peuvent entraîner des
résultats trop faibles.
Les interférences dues aux métaux lourds sont moins nombreuses si l’agent réducteur utilisé est le chlorure d'étain
(II) et non le tétrahydroborate de sodium. En utilisant des systèmes à flux continu, les interférences dues aux
métaux lourds peuvent être inférieures aux valeurs mentionnées dans le Tableau 1.
L'utilisation de chlorure d’étain (II) entraîne une telle contamination de l'appareillage par l'étain qu’il peut se
produire des interférences considérables si l’on utilise ensuite du tétrahydroborate de sodium. Des systèmes
séparés sont donc utilisés pour la réduction avec le chlorure d'étain(II) etcelleavec letétrahydroborate de sodium.
2 © ISO 2000 – Tous droits réservés
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ISO 16590:2000(F)
Tableau 1 — Concentrations acceptables de certains élémentsde lamatriceprésents
dans la solution de mesurage
Agent réducteur NaBH NaBH SnCl
4 4 2
Milieu
HCl à 0,5 mol/l HCl à 5 mol/l + Fe (III) à 0,2 g/l HCl à 0,5 mol/l
Élément Concentration acceptable (mg/l)
Cu (II) 10 10 500
Ni (II) 1 500 500
Ag (I) 0,1 10 1
– 100 10 0,1
I
As (V) 0,5 0,5 0,5
Bi(III) 0,05 0,5 0,5
Sb(III) 0,5 0,5 0,5
Se(IV) 0,005 0,05 0,05
4 Dosage du mercure aprèsréduction avec le chlorure d'étain (II) et enrichissement par
amalgame
4.1 Gamme de mesure
Cette méthode convient pour le dosage de teneurs en mercure dans le domaine de concentration allant de
0,01�g/l à 1�g/l. Des concentrations plus élevées peuvent également être déterminées par dilution de l'échantillon
d'eau.
NOTE Les mesurages effectués dans ce domaine de concentration nécessitent l'emploi de réactifs de pureté maximale, de
fioles propres, d'une atmosphère de laboratoire exempte de mercure et d'un système de mesurage présentant une très bonne
stabilité.
4.2 Principe
Le mercure est réduit à sa forme élémentaire par le chlorure d'étain (II) et transporté dans un courant de gaz inerte
ayant une teneur en mercure négligeable, sur une large surface de métal précieux, telle qu'une gaze en or/platine,
sur laquelle le mercure est adsorbé.
Le mercure est libéré par chauffage rapide de l'adsorbant, puis transporté dans un courant de gaz vecteur vers la
cellule d'absorption, où l'absorbance est mesurée à 253,7 nm.
4.3 Interférences
Voir également article 3.
Les teneurs en iodure � 0,1 mg/l provoquent des interférences dans la détermination, dues à la formation de
complexes de mercure. Dans ce cas, utiliser une autre méthode comme la réduction par le tétrahydroborate de
sodium (voir article 5).
En raison du potentiel de réductiondelasolutiondechlorured'étain (II), divers composés inorganiques du mercure
tels que le sulfure de mercure et les composés organiques du mercure, ne peuvent être réduits complètement sans
digestion.
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ISO 16590:2000(F)
4.4 Réactifs
Utiliser des réactifs qui soient au moins de «qualité analytique», ou avec une teneur en mercure la plus faible
possible. La teneur en mercure de l'eau et des réactifs doit être négligeable par rapport à la plus faible
concentration à déterminer.
4.4.1 Eau, bidistilléeoudepuretééquivalente, pour préparer les solutions.
4.4.2 Acide nitrique,� (HNO ) = 1,40 g/ml
3
4.4.3 Acide sulfurique,� (H SO ) = 1,84 g/ml
2 4
4.4.4 Acide chlorhydrique,� (HCl) = 1,19 g/ml
4.4.5 Solution de permanganate de potassium.
Dissoudre 50 g de permanganate de potassium, KMnO , dans 1 000 ml d'eau.
4
4.4.6 Agent stabilisant.
Dissoudre 5 g de bichromate de potassium, K Cr O , dans 500 ml d'acide nitrique (4.4.2), et diluer à 1 000 ml avec
2 2 7
de l'eau.
AVERTISSEMENT — Le bichromate de potassium est toxique. Il convient d'être prudent lors de la
manipulation du matériau solide ou de ses solutions.
4.4.7 Solution de peroxodisulfate de potassium.
Dissoudre 40 g de peroxodisulfate de potassium, K S O , dans 1 000 ml d'eau.
2 2 8
4.4.8 Solution de chlorure d'hydroxylamine.
Dissoudre 10 g de chlorure d'hydroxylamine, H NOH, HCl dans 100 ml d'eau.
2
4.4.9 Solution de chlorure d'étain (II).
Dissoudre 5 g de chlorure d'étain (II) dihydraté,SnCl ,2H O, dans 30 ml d'acide chlorhydrique (voir 4.4.4) et diluer
2 2
à 100 ml avec de l'eau. Dans le cas de systèmes à flux continu, il est possible d'utiliser une solution de
concentration plus faible, de 0,5 g dans 100 ml, par exemple. Préparer cette solution fraîchement chaque jour par
dilution dans l'eau, de la solution la plus concentrée.
En cas d'obtention d'une valeur à blanc élevée, purger la solution à l'azote pendant 30 min afin d'éliminer les traces
de mercure.
4.4.10 Solution mère de mercure I,� (Hg) = 100 mg/l.
Dissoudre 108,0 mg d'oxyde de mercure (II), HgO, dans 10 ml de l'agent stabilisant (4.4.6) et diluer à 1 000 ml
avec de l'eau. 1 ml de la solution correspond à 0,1 mg de mercure.
Il est possible de préparer la solution mère I à partir d'une solution étalon de mercure disponible dans le
commerce. Cette solution est stable pendant environ 1 mois.
4 © ISO 2000 – Tous droits réservés
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ISO 16590:2000(F)
4.4.11 Solution mère de mercure II,� (Hg) = 1 mg/l.
Ajouter 10 ml d'agent stabilisant (4.4.6) à 10 ml de la solution mère I (voir 4.4.10) et diluer à 1 000 ml avec de l'eau.
1 ml de cette solution correspond à 1�g de mercure. Cette solution reste stable pendant environ une semaine.
4.4.12 Solution étalon de mercure I,� (Hg) = 100�g/l
Ajouter 10 ml d'agent stabilisant (4.4.6) à 100 ml de la solution mère II (4.4.11) et diluer à 1 000 ml avec de l'eau.
1 ml de cette solution correspond à 100 ng de mercure.
Préparer cette solution le jour de son utilisation.
4.4.13 Solution étalon de mercure II,� (Hg) = 10�g/l.
Diluer 1 ml de la solution d'agent stabilisant (4.4.6) et 10 ml de la solution étalon I (4.4.12) dans 100 ml d'eau. 1 ml
de cette solution correspond à 10 ng de mercure. Cette solution n'est stable que pendant une courte duréeet doit
être fraîchement préparée avant son utilisation.
4.4.14 Solution étalon de mercure III,� (Hg) = 1�g/l.
Diluer 1 ml de la solution d'agent stabilisant (4.4.6) et 10 ml de la solution étalon II (4.4.13) dans 100 ml d'eau. 1 ml
de cette solution correspond à 1 ng de mercure. La solution doit être préparéefraîchement avant chaque série de
mesurages.
4.4.15 Solutions de mercure pour l’étalonnage.
Préparer des solutions d'étalonnage appropriées au volume et aux concentrations en mercure attendues des
solutions de mesurage.
Pour la gamme de concentrations allant de 0,01�g/l à 0,1�g/l, par exemple, procéderdelamanière suivante.
� Au moyen d'une pipette, introduire dans chacune des six fioles jaugées de 100 ml, respectivement 1,0 ml,
2,0ml, 4,0ml, 6,0ml, 8,0ml ou 10ml de solution étalon de mercure III (4.4.14).
� Ajouter 1 ml de solution d'agent stabilisant (4.4.6) à chaque solution.
� Compléter chaque fiole jusqu'au trait avec de l'eau et mélanger soigneusement.
Les solutions d'étalonnage contiennent respectivement 0,01�g/l, 0,02�g/l, 0,04�g/l, 0,06�g/l, 0,08�g/l et 0,1�g/l
de mercure. Elles doivent être fraîchement préparées avant chaque série de mesurages.
Pour la gamme de concentrations allant de 0,1�g/l à 1�g/l, procéder de manière identique en utilisant la solution
étalon de mercure II (4.4.13). Dans ce cas, les solutions de référence contiennent respectivement 0,1�g/l, 0,2�g/l,
0,4�g/l, 0,6�g/l, 0,8�g/l et 1�g/l de mercure. En cas d'utilisation de plus grands volumes de solution de
mesurage, il est nécessaire d'augmenter proportionnellement le volume respectif des solutions de référence ainsi
que la quantité de solution étalon ajoutée. Les solutions doivent être fraîchement préparées avant chaque série de
mesurages.
Lorsque les mesurages d'étalonnage doivent être effectués en double, préparer une série supplémentaire de
solutions.
4.4.16 Solution du blanc réactif.
Préparer un volume de la solution à blanc correspondant à celui de la solution de mesurage, en diluant 10 ml
d'agent stabilisant (4.4.6) à 1 000 ml avec de l'eau. Utiliser le même procédé de digestion que pour l'échantillon
(voir 4.7). Le blanc réactif doit être inclus dans chaque série d'analyses.
© ISO 2000 – Tous droits réservés 5
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ISO 16590:2000(F)
4.4.17 Solution de lavage des gaz.
Dissoudre 2,5 g de chlorure d'étain (II) dihydraté,SnCl ,2H O avec 7,5 ml d'acide sulfurique (4.4.3) dans une petite
2 2
quantité d'eau, puis diluer à 50 ml avec de l'eau.
4.4.18 Solution de lavage de la verrerie.
Diluer 150 ml d'acide nitrique (4.4.2) à 1 000 ml avec de l'eau.
4.5 Appareillage
Toute la verrerie doit être nettoyée soigneusement avant utilisation avec de l’acide nitrique dilué (4.4.18), puis
soigneusement rincée plusieurs fois avec de l’eau.
4.5.1 Spectromètre d'absorption atomique (SAA), muni d'un système d'enregistrement approprié.Ilest
conseillé d'utiliser un système permettant une correction de l'absorption non spécifique.
4.5.2 Source de rayonnement, pour le dosage du mercure, par exemple, lampe à cathode creuse ou lampe à
décharge sans électrode.
4.5.3 Dispositif complémentaire, comprenant:
� des cellules d’absorption constituées d’un tube de verre ou de quartz, de diamètre intérieur d’environ 2 cm,
d’au moins 15 cm de longueur (selon le spectromètre d’absorption atomique), et munies de fenêtres en quartz;
� une pompe de circulation d'air (pompe à membrane, pompe péristaltique, par exemple), ayant un débit de
1l/min à 2 l/min et munie de tubes en plastique (système fermé);
� une bouteille de gaz inerte (par exemple azote ou argon), avec teneur en mercure négligeable, équipéede
régulateur de pression;
� un débitmètre muni de tubes en plastique (voir article 3);
� un récipient de réaction comprenant, par exemple, des ballons à fond plat de 100 ml, 250 ml ou 1 000 ml tels
qu'illustrés sur la Figure 1, munis de bouchons en verre rodé, d'un flacon laveur avec verre fritté de porosité 1;
� une source de chaleur destinée à la cellule de mesurage, d’une capacité de chauffage suffisante pour prévenir
la condensation d'eau; la température de la cellule de mesurage doit rester constante tout au long de l'analyse;
� un tube de quartz muni d'un élément chauffant et d'un adsorbant en métal précieux (tel qu'une gaze en
or/platine);
� un barboteur à gaz de 100 ml, équipé d'une soupape de protection contre les retours;
� un robinet d'arrêt à trois voies.
Un exemple de système fermé est représentéà la Figure 1.
NOTE Il convient d'être vigilant lors du choix des matières plastiques composant les pompes et les tubes (voir article 3).
L'usage d'un système à flux continu ou à flux injecté est permis. Il est recommandé de se conformer aux instructions fournies
par le fabricant.
6 © ISO 2000 – Tous droits réservés
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ISO 16590:2000(F)
Légende
1 Pompe de circulation d’air, de débit compris entre 1 l/min et 2 l/min
2Débitmètre
3 Robinet d’arrêt à trois voies
4 Cellule d’absorption, diamètre intérieur: 2 cm; longueur: 15 cm
5 Gaze Au-Pt
6 Vanne de protection contre les retours
7 Bouchon en verre rodé
8 Ballon de réaction de 100 ml, 250 ml ou 1000 ml
9SnCl dans H SO
2
2 4
10 Gaz inerte
11 Dispositif chauffant
Figure 1 — Dispositif complémentaire pour le dosage du mercure par le chlorure d’étain (II)
et enrichissement par amalgame (système fermé)
4.6 Échantillonnage et prétraitement de l’échantillon
Lors de l'échantillonnage et du prétraitement, les exigences de l'ISO 5667-1, l'ISO 5667-2 et l'ISO 5667-3 doivent
être prises en compte.
Les matériaux appropriéspourles récipients d'échantillonnage sont le verre borosilicaté, le quartz, le polysulfone
(PSF) et le copolymère de l’(éthylène/propylène)perfluoré (FEP).
Veiller à ce que le récipient d'échantillonnage soit exempt de mercure et qu'il ne provoque aucune perte de
mercure par adsorption.
Pour limiter les pertes dues, par exemple, à l'adsorption sur les parois du récipient, ajouter 10 ml d'agent stabilisant
(4.4.6) et compléter à 1 000 ml avec l'échantillon.
L'échantillon doit avoir un pH d’environ 1 et une teinte jaune orangée indiquant un excès de dichromate.
© ISO 2000 – Tous droits réservés 7
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ISO 16590:2000(F)
Si ces conditions ne sont pas remplies, ajouter une quantité supplémentaire d'agent stabilisant et inclure le facteur
approprié de correction du volume dans les calculs.
4.7 Méthode de digestion au permanganate et peroxodisulfate
Il convient d’effectuer le mode opératoire de digestion chimique par voie humide décrit ci-après. Il est également
possible d'utiliser une méthode de digestion telle que celles décrites dans les annexes A à C. Dans ce dernier cas,
l'efficacité de la méthode utiliséedoit être comparée àcelledelaméthode de digestion par voie humide.
Transvaser 100 ml d'échantillon d'eau stabilisé (voir 4.6) ou un volume approprié (n'excédant pas 1 000 ml)
d'échantillon dans une fiole constituéedel'un des matériaux citésen 4.6.
Ajouter avec précaution 15 ml de solution de permanganate de potassium (4.4.5), 1 ml d'acide nitrique (4.4.2) et
1 ml d'acide sulfurique (4.4.3).
Bien agiter le mélange après chaque ajout.
Laisser la solution reposer pendant 15 min, puis ajouter 10 ml de solution de peroxodisulfate de potassium (4.4.7).
Placer la fiole, bouchon entrouvert, sur un bloc chauffant ou dans un bain d'eau à 95 °Cetl’y laisser 2 h.
Durant la digestion, s'assurer de la présenced'unexcès de permanganate de potassium. Si ce n’est pas le cas,
augmenter la quantité de permanganate de potassium ajouté ou recommencer avec un volume d'échantillon plus
faible.
Laisser la solution refroidir à température ambiante.
En cas d'utilisation de volumes d'échantillon différents, et par conséquent de différents volumes de réactifs, diluer
les solutions de digestion à un volume spécifique.
Procéder le plus rapidement possible à l'analyse de ces solutions.
Préparer de manière analogue une solution de blanc réactif (4.4.16) en utilisant le volume d'eau correspondant
(4.4.1) contenant l'agent stabilisant (4.4.6) au lieu de l'échantillon d'eau.
Le permanganate peut provoquer des problèmes de blanc. Dans ce cas, réduire la concentration du permanganate
sous réserve que la teneur en matières organiques soit faible; il est également possible d’utiliser une autre
méthode de digestion (voir annexes A à C).
4.8 Mode opératoire
4.8.1 Préparation du dosage
Avant de procéder au mesurage, régler les paramètres de l'appareil selon les instructions du fabricant et aligner la
cellule d'absorption.
Si la solution de digestion a été préparée conformément aux instructions du 4.7, ajouter immédiatement avant le
mesurage 5 ml (ou plus, si nécessaire) de solution de chlorure d'hydroxylamine (4.4.8) à la totalité de la solution de
digestion. 5 ml de solution de chlorure d'hydroxylamine sont généralement suffisants pour réduire l'excès d'agents
oxydants et pour dissoudre le précipité de dioxyde de manganèse. Si la solution n'est pas devenue limpide au bout
de 30 min, ajouter une quantité supplémentaire de chlorure d'hydroxylamine.
Si une portion aliquote de l'échantillon est prélevée pour l'analyse, compléter au préalable la solution d'échantillon
à un volume spécifique, par exemple 200 ml.
Transvaser la solution de mesurage (solution de digestion ou aliquote) dans le récipient de réaction et raccorder au
dispositif d'analyse.
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ISO 16590:2000(F)
Ajouter 2 ml de solution de chlorure d'étain (II) (4.4.9) à 100 ml (ou moins) de solution de mesurage.
Si l'agent de réduction doit être ajouté manuellement, raccorder le récipient de réaction à l'appareil immédiatement
après l'ajout de la solution de chlorure d'étain (II).
Pour des volumes plus importants de solution de mesurage (jusqu'à 1 000 ml), augmenter le volume d'agent de
réduction jusqu'à une valeur maximale de 5 ml.
En système fermééquipé d'une pompe de circulation d'air, faire passer le gaz inerte, à un débit de 1 l/min à 2l/min
à travers le récipient de réaction et l'adsorbant en métal précieux. Lorsque l’adsorption est complète, éteindre la
pompe et ouvrir le robinet d'arrêt à trois voies.
En système ouvert, entraîner l'échantillon d'eau dans un courant de gaz inerte ayant une teneur négligeable en
mercure.
Libérer le mercure adsorbé par chauffage rapide de l'adsorbant à au moins 600 °C.
Transporter dans la cellule d'absorption, les vapeurs de mercure dans un courant de gaz inerte à 75 ml/min, par
exemple, qui ne doit pas traverser la solution de mesurage, puis mesurer la hauteur du pic ou, de préférence, la
surfacedupic.
Effectuer le mesurage de la solution d'étalonnage (4.4.15) et du blanc réactif (4.4.16) de la même manière que
pour l'échantillon d'eau.
4.8.2 Analyse à l’aide de la méthode par étalonnage standard
Pour les besoins de l'analyse, une courbe d'étalonnage doit être élaboréedelamanière suivante.
Préparer les solutions d'étalonnagedemercureselon4.4.15.
Mesurer l'absorbance respective des solutions d'étalonnage et de la solution à blanc selon la description donnée
en 4.8.
Établir l'équation de la droite d'étalonnage linéaire à partir des séries de résultats obtenus.
4.8.3 Analyse à l'aide de la méthode d'étalonnage par ajouts dosés
Si la méthode d'étalonnage standard ne permet pas l'obtention de résultats suffisamment exacts, par exemple en
raison d'effets de matrice, utiliser la méthode des ajouts dosés, à condition que ne survienne aucune erreur
supplémentaire et que les absorbances des échantillons d'eau dopés se situent dans la gamme de travail linéaire,
c'est-à-dire que les résultats soient dans la zone linéaire de la courbe d'étalonnage. La concentration du mercure
ajouté doit correspondre à la teneur en mercure attendue dans l'échantillon. À titre d'exemple, pour un volume
d'échantillon de 50 ml et une concentration en mercure attendue de 0,1�g/l, procéder de la manière suivante.
Introduire 50 ml de la solution de mesurage (voir 4.8.1) dans chacun des quatre ballons de réaction de 100 ml.
Dans trois de ces ballons, ajouter respectivement 0,5 ml, 1,0 ml ou 1,5 ml de solution étalon de mercure II
(4.4.13). Les ajouts dosés correspondent respectivement à 0,1�g/l, 0,2�g/l et 0,3�g/l de mercure.
Mesurer la concentration en mercure des quatre ballons conformément aux instructions du 4.8.
Pour la solution de blanc réactif (4.4.16), suivre le
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