EN ISO 6978-1:2005

SLOVENSKI STANDARD
01-julij-2005
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Natural gas - Determination of mercury - Part 1: Sampling of mercury by chemisorption
on iodine (ISO 6978-1:2003 )
Erdgas - Bestimmung von Quecksilber - Teil 1: Probenahme von Quecksilber durch
Chemisorption an lod (ISO 6978-1:2003)
Gaz naturel - Détermination de la teneur en mercure - Partie 1: Echantillonnage de
mercure par chimisorption sur iode (ISO 6978-1:2003)
Ta slovenski standard je istoveten z: EN ISO 6978-1:2005
ICS:
75.060 Zemeljski plin Natural gas
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 6978-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2005
ICS 75.060
English version
Natural gas - Determination of mercury - Part 1: Sampling of
mercury by chemisorption on iodine (ISO 6978-1:2003 )
Gaz naturel - Détermination de la teneur en mercure - Erdgas - Bestimmung von Quecksilber - Teil 1:
Partie 1: Echantillonnage de mercure par chimisorption sur Probenahme von Quecksilber durch Chemisorption an lod
iode (ISO 6978-1:2003) (ISO 6978-1:2003)
This European Standard was approved by CEN on 17 April 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6978-1:2005: E
worldwide for CEN national Members.

Foreword
The text of ISO 6978-1:2003 has been prepared by Technical Committee ISO/TC 193 "Natural
gas” of the International Organization for Standardization (ISO) and has been taken over as EN
ISO 6978-1:2005 by CMC.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by November 2005, and conflicting national
standards shall be withdrawn at the latest by November 2005.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 6978-1:2003 has been approved by CEN as EN ISO 6978-1:2005 without any
modifications.
INTERNATIONAL ISO
STANDARD 6978-1
First edition
2003-10-15
Natural gas — Determination of
mercury —
Part 1:
Sampling of mercury by chemisorption
on iodine
Gaz naturel — Détermination de la teneur en mercure —
Partie 1: Échantillonnage de mercure par chimisorption sur iode

Reference number
ISO 6978-1:2003(E)
©
ISO 2003
ISO 6978-1:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 6978-1:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Principle . 2
5 Apparatus. 2
6 Reagents . 9
7 Sampling . 10
7.1 General. 10
7.2 Sampling procedure (see Figures 1 and 2). 11
7.3 Sample treatment . 12
8 Mercury determination . 13
8.1 Transfer of mercury to AAS or AFS instrument. 13
8.2 Calibration. 13
8.3 Blank test . 13
9 Calculation. 14
10 Precision . 15
10.1 General. 15
10.2 Repeatability and reproducibility . 15
10.3 Uncertainty. 15
11 Test report. 15
Bibliography . 16

ISO 6978-1:2003(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 6978-1 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of
natural gas.
This first edition of ISO 6978-1, together with ISO 6978-2, cancels and replaces ISO 6978:1992, which has
been technically revised.
ISO 6978 consists of the following parts, under the general title Natural gas — Determination of mercury:
 Part 1: Sampling of mercury by chemisorption on iodine
 Part 2: Sampling of mercury by amalgamation on gold/platinum alloy
iv © ISO 2003 — All rights reserved

ISO 6978-1:2003(E)
Introduction
Natural gases may contain considerable amounts of mercury, which are generally present in the elemental
form. Gases with high mercury content have to be purified to avoid the condensation of mercury during
processing and transport as well as to be compliant with the demands of gas sales contracts. Low mercury
concentrations are specified when natural gas is to be liquefied. This is to avoid severe corrosion problems,
for instance in aluminium heat exchangers of liquefaction plants.
Since the presence of hydrocarbons, in particular aromatic hydrocarbons present in low concentrations in
almost every natural gas, interferes in the determination of mercury by atomic absorption spectrometry (AAS)
or atomic fluorescence spectrometry (AFS), mercury cannot be determined directly in natural gas. Therefore,
prior to the analytical determination, mercury has to be collected and separated from aromatic hydrocarbons.
The purpose of the determination of the mercury content can be
 to monitor gas quality,
 to monitor the operation of gas treatment plants for mercury removal.
Several methods for the collection or enrichment of mercury from natural gas have been developed. The
collection of mercury from dry natural gas normally poses no particular problem. However, care should be
taken when sampling mercury from natural gases under nearly condensing conditions (see ISO 6570).
The two parts of ISO 6978 describe the principles of sampling and specify the general requirements for
methods for sampling mercury and for determining total mercury in pipeline quality natural gas. This part of
ISO 6978 specifies a method of sampling mercury by chemisorption on iodine-impregnated silica gel whereas
Part 2 specifies a method of sampling mercury by amalgamation on gold/platinum alloy thread.

INTERNATIONAL STANDARD ISO 6978-1:2003(E)

Natural gas — Determination of mercury —
Part 1:
Sampling of mercury by chemisorption on iodine
WARNING — The use of this part of ISO 6978 may involve hazardous materials, operations and
equipment. This part of ISO 6978 does not purport to address all of the safety problems, associated
with its use. It is the responsibility of the user of this part of ISO 6978 to establish appropriate safety
and health practices and to determine the applicability or regulatory limitations prior to use.
1 Scope
This part of ISO 6978 specifies a method for the determination of total mercury content in natural gas using a
sampling method at pressures up to 40 MPa by chemisorption on iodine-impregnated silica gel. This sampling
3 3
method is suitable for the determination of mercury contents within the range of 0,1 µg/m to 5 000 µg/m in
natural gas. This method is applicable to sampled gas volumes containing less than 20 mg hydrogen sulfide
(absolute content) and less than a total liquid hydrocarbon condensate of 10 g/m under the sampling
conditions. The collected mercury is determined by measuring the absorbance or fluorescence of mercury
vapour at 253,7 nm.
NOTE ISO 6978-2 gives a sampling method suitable for the determination of mercury content of pipeline natural gas
by amalgamation of mercury on gold/platinum alloy thread at atmospheric pressure for the range of mercury from
3 3 3 3
0,01 µg/m to 100 µg/m and for sampling at high pressure (up to 8 MPa) from 0,001 µg/m to 1 µg/m .
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 6570, Natural gas — Determination of potential hydrocarbon liquid content — Gravimetric methods
ISO 10715, Natural gas — Sampling guidelines
ISO 14111, Natural gas — Guidelines to traceability in analysis
ISO 14532, Natural gas — Vocabulary
Guide to the expression of uncertainty in measurement (GUM), BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML
1)
AISI Steel Code
1) Available from the American Iron and Steel Institute, c/o James McCarl, 131 Huron Drive, Carnegie, PA 15106, USA.
ISO 6978-1:2003(E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 apply.
4 Principle
The gas is passed through a glass tube containing silica gel impregnated with iodine. Mercury (Hg) present in
the gas as elemental mercury or organic mercury compounds [e.g. dimethyl mercury, Hg(CH ) , or diethyl
3 2
mercury, Hg(C H ) ] is chemisorbed:
2 5 2
Hg + I → HgI
2 2
Hg(CH ) + 2 I → HgI + 2 CH I
3 2 2 2 3
The mercury iodide (HgI ) formed is then dissolved in an ammonium iodide/iodine solution (NH I/I ) in the
2 4 2
laboratory. Hydrocarbon condensates are removed by vacuum stripping at this stage. Mercury, present in the
form of a water-soluble complex, is determined by reducing aliquot portions of this solution with alkaline tin(II)
solution to elemental mercury. The mercury is stripped from the solution by an inert gas and the mercury
vapour is transferred to a cold vapour atomic absorption spectrometer (AAS) or atomic fluorescence
spectrometer (AFS) for measurement at 253,7 nm. Calibration for the final mercury determination is performed
in the same way using an aqueous mercury standard solution which is matrix-matched to the sample.
Unless otherwise specified, gas volumes are expressed in cubic metres (m ) at 273,15 K and 1 013,25 hPa.
5 Apparatus
The parameters influencing the measurement shall be traceable to national or International Standards. The
uncertainty of the volume measurement (volume, temperature and pressure of the gas as well as ambient air
pressure) directly contributes to the uncertainty of the determined mercury content of the gas. Therefore
suitable measuring equipment, calibrated against a commonly accepted reference, shall be used to minimize
the uncertainty of the volume measurement to less than 1 %.
5.1 Sampling apparatus [see Figure 1 a) for sampling up to 10 MPa and Figure 1 b) for up to 40 MPa],
comprising the following:
5.1.1 High-pressure sampling cell (see Figure 1 with details given in Figure 2), made of NiMo16Cr15W
(material no. 2.4819 in accordance with the Steel Code), which includes a temperature gauge and a pressure
gauge and the following components.
5.1.1.1 Acid-washed glass wool.
5.1.1.2 Sampling tube (see Figure 1 with details given in Figure 3), made of borosilicate glass and fitted
with a screw cap.
Fit the sampling tube (Figure 3) first with a layer, 0,5 cm thick, of acid-washed glass wool (5.1.1.1) to retain
the absorbent. Then fill the tube with 4,00 g of iodine-laden silica gel (6.2.3) to obtain a 5 cm absorption layer.
Then add another layer, 0,5 cm thick, of glass wool (5.1.1.1) to retain the top of the absorbent layer. Close the
tube with a screw cap.
5.1.2 Temperature gauges or thermometers (see Figure 1 with details given in Figure 2).
5.1.3 Pressure gauges (see Figure 1 with details given in Figure 2).
5.1.4 Pressure relief valves (see Figure 1) which are either
a) electrically heated, for sampling pressure up to 10 MPa [see Figure 1 a)], or
b) coupled with a heat exchanger (5.1.5), for sampling pressure up to 40 MPa [see Figure 1 b)].
2 © ISO 2003 — All rights reserved

ISO 6978-1:2003(E)
When positioned in a hazardous area, the electrically heated pressure relief valve shall comply with local
safety regulations.
5.1.5 Heat exchanger [see Figure 1 b)], with sufficient capacity to heat sample and bypass gas to 90 °C.
When positioned in a hazardous area, the heat exchanger shall comply with local safety regulations.
5.1.6 Gas meter (see Figure 1), equipped with a thermometer (5.1.2) and a pressure gauge (5.1.3).
5.1.7 Barometer, required for measuring the ambient air pressure.
5.2 Glass apparatus for dissolution (see Figure 4), for the dissolution of mercury iodide and consisting of
the following.
5.2.1 Reservoir, for the solution.
5.2.2 Graduated receiver.
5.2.3 Stop cocks.
5.2.4 Three-way valve.
5.3 Glass apparatus for charging of silica gel with iodine (see Figure 5), comprising the following.
5.3.1 Round bottom flask, of 2 l capacity.
5.3.2 Gas inlet tube.
5.3.3 Air filter, filled with a suitable absorbent, such as sulfur-impregnated activated charcoal, to remove
mercury from the air.
5.4 Cold vapour atomic absorption spectrometer (AAS) or atomic fluorescence spectrometer (AFS).
A cold vapour technique AAS with back
...