SIST EN ISO 6978-2:2005

SLOVENSKI STANDARD
SIST EN ISO 6978-2:2005
01-julij-2005
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Natural gas - Determination of mercury - Part 2: Sampling of mercury by amalgamation
on gold/platinum alloy (ISO 6978-2:2003)
Erdgas - Bestimmung von Quecksilber - Teil 2: Probenahme von Quecksilber durch
Amalgamierung an einer Gold/Platin-Legierung (ISO 6978-2:2003)
Gaz naturel - Détermination de la teneur en mercure - Partie 2: Echantillonnage du
mercure par amalgamation sur alliage or/platine (ISO 6978-2:2003)
Ta slovenski standard je istoveten z: EN ISO 6978-2:2005
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 6978-2:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6978-2:2005

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SIST EN ISO 6978-2:2005
EUROPEAN STANDARD
EN ISO 6978-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2005
ICS 75.060
English version
Natural gas - Determination of mercury - Part 2: Sampling of
mercury by amalgamation on gold/platinum alloy (ISO 6978-
2:2003)
Gaz naturel - Détermination de la teneur en mercure - Erdgas - Bestimmung von Quecksilber - Teil 2:
Partie 2: Echantillonnage du mercure par amalgamation sur Probenahme von Quecksilber durch Amalgamierung an
alliage or/platine (ISO 6978-2:2003) einer Gold/Platin-Legierung (ISO 6978-2:2003)
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 6978-2:2005: E
worldwide for CEN national Members.

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SIST EN ISO 6978-2:2005
EN ISO 6978-2:2005 (E)






Foreword



The text of ISO 6978-2:2003 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 6978-2:2005 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 6978-2:2003 has been approved by CEN as EN ISO 6978-2:2005 without any
modifications.

2

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SIST EN ISO 6978-2:2005


INTERNATIONAL ISO
STANDARD 6978-2
First edition
2003-10-15


Natural gas — Determination of
mercury —
Part 2:
Sampling of mercury by amalgamation on
gold/platinum alloy
Gaz naturel — Détermination de la teneur en mercure —
Partie 2: Échantillonnage du mercure par amalgamation sur alliage
or/platine




Reference number
ISO 6978-2:2003(E)
©
ISO 2003

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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
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ii © ISO 2003 — All rights reserved

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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 1
5 Apparatus. 2
6 Reagents and materials. 8
7 Preparation of sampling and analytical tubes . 9
7.1 Filling. 9
7.2 Cleaning . 9
7.3 Efficiency testing . 9
8 Sampling . 9
8.1 General. 9
8.2 Conditions for representative sampling. 10
8.3 Sampling procedure at atmospheric pressure (see Figure 1). 10
8.4 Sampling procedure at high pressure (see Figure 4). 11
8.5 Removal of condensate from discarded sampling tubes. 12
9 Mercury determination . 12
9.1 Transfer of mercury to the analytical tube (double amalgamation) . 12
9.2 Transfer of mercury to AAS or AFS instrument. 13
9.3 Calibration. 13
9.4 Blank test . 13
10 Calculation. 13
11 Precision . 16
12 Test report. 16
Bibliography . 17

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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(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 6978-2 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of
natural gas.
This first edition of ISO 6978-2, together with ISO 6978-1, 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
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(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 amalgamation on gold/platinum alloy thread whereas
Part 1 specifies a method of sampling mercury by chemisorption on iodine-impregnated silica gel.

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SIST EN ISO 6978-2:2005

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SIST EN ISO 6978-2:2005
INTERNATIONAL STANDARD ISO 6978-2:2003(E)

Natural gas — Determination of mercury —
Part 2:
Sampling of mercury by amalgamation on gold/platinum alloy
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 of pipeline quality
natural gas using a sampling method by amalgamation on gold/platinum (Au/Pt) alloy thread. This method is
applicable to the sampling of raw natural gas when no condensation is present. At atmospheric pressure, this
3 3
method is suitable for the determination of mercury content within the range of 0,01 µg/m to 100 µg/m in
natural gas samples. At higher pressures (up to 8 MPa), this sampling method is suitable for the determination
3 3
of mercury contents within the range of 0,001 µg/m to 1 µg/m . The collected mercury is determined by
measuring the absorbance or fluorescence of mercury vapour at 253,7 nm.
NOTE ISO 6978-1 gives a sampling method suitable for the determination of mercury contents in natural gas by
3 3
chemisorption on iodine-impregnated silica gel for the working range of 0,1 µg/m to 5 000 µg/m for sampling at
pressures up to 40 MPa.
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 10715, Natural gas — Sampling guidelines
ISO 14532, Natural gas — Vocabulary
Guide to the expression of uncertainty in measurement (GUM), BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 apply.
4 Principle
Sampling is performed at a temperature at least 10 °C higher than the dewpoint of the gas sampled. The gas
is passed through two quartz glass sampling tubes in series containing fine gold/platinum alloy thread. The
mercury is collected on the gold/platinum alloy thread by amalgamation. Subsequently, each sampling tube is
separately heated to 700 °C to desorb the mercury from the amalgam. The released mercury is transferred by
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
a stream of air onto an analytical tube filled with gold/platinum alloy thread (double amalgamation). This
second quartz glass tube is then heated to 800 °C and the mercury is transferred to an AAS or AFS for
measurement at 253,7 mm.
This sampling method is suitable for the determination of mercury content in natural gas in the range of
3 3 3 3
0,01 µg/m to 100 µg/m for sampling at atmospheric pressure and 0,001 µg/m to 1 µg/m for sampling at
high pressure. To avoid diffusion of mercury from the surface into the gold/platinum alloy thread, which would
reduce the recovery of mercury under the specified transfer conditions, it is necessary to determine the
amount of collected mercury within one week after sampling.
Other sorption materials such as gold-impregnated silica with a high specific surface may be used instead of
fine gold/platinum alloy thread, provided they show equivalent method performance in the natural gas matrix.
3
Unless otherwise specified, gas volumes are expressed in cubic metres (m ) at 273,15 K and 1 013,25 hPa.
NOTE The comparability of the two sampling techniques has been demonstrated by interlaboratory tests at two
different concentration levels.
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).
5.1.1 Apparatus for sampling at atmospheric pressure, typically comprising the following:
5.1.1.1 Heated bypass valve.
5.1.1.2 Heated flow control valve (needle type).
5.1.1.3 Three-way valve, for the second bypass.
5.1.1.4 Aluminium block, capable of being heated to u 100 °C (see Figure 2) and dividable into two
halves with a central bore coated with a layer (about 2 mm) of silicon rubber for keeping the quartz glass
sampling tubes filled with gold/platinum alloy thread (see Figure 3) during sampling at elevated temperature (if
necessary) and equipped with a temperature gauge (not shown in Figure 1).
5.1.1.5 Flow meters (three):
 one for flowrates u 50 l/min;
 two for flowrates u 5 l/min.
5.1.1.6 Gas meter, suitable for measuring flowrates of u 5 l/min, capable of allowing adjustment of the
bypass flow and the volume measurement and equipped with the following:
a) pressure gauge;
b) temperature gauge, for measuring temperatures between 0 °C to 40 °C.
5.1.1.7 Barometer, required for measuring the ambient air pressure.
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)

Key
1 pipeline 7 three-way valve
2 sampling valve 8 aluminium block for heating
3 first bypass 9 flow indicator
4 bypass valve 10 gas meter
5 flow control valve 11 temperature gauge
6 second bypass 12 pressure gauge
Figure 1 — Sampling apparatus
Dimensions in millimetres

Key
1 heating plug
2 silicon rubber (glued)
3 division line
Figure 2 — Heating box (heatable aluminium box)
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
Dimensions in millimetres

Key
1 gold/platinum wire (350 Au/150 Pt alloy)
2 indentation
3 O-ring
Figure 3 — Quartz glass sampling and analytical tubes
5.1.2 Apparatus for sampling at high pressure (see Figure 4), comprising the following:
5.1.2.1 Pressure gauge, suitable for measuring pressures from 0 MPa to 25 MPa.
5.1.2.2 Valve.
5.1.2.3 Bypass valve.
5.1.2.4 Pressure-reducing valves (two).
5.1.2.5 Three-way valve.
5.1.2.6 Pressure relief valves (two), set at pressures of 10 MPa and 4 kPa, respectively, to protect the
high-pressure vessel and the gas meter against over pressure.
5.1.2.7 Pressure gauge, suitable for measuring pressures from 0 MPa to 10 MPa in the high-pressure
vessel.
5.1.2.8 Flow indicator, for adjusting the gas flow through the high-pressure vessel.
5.1.2.9 Heating tape, for wrapping around the assembly except for the relieve valves and the flow
indicator.
5.1.2.10 Gas meter, for measuring sample volumes and suitable for a gas flowrates of u 50 l/min and
equipped with the following:
a) pressure gauge;
b) temperature gauge, for measuring temperatures between 0 °C to 40 °C.
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
5.1.2.11 Barometer, required for measuring the ambient air pressure.
5.1.2.12 High-pressure vessel (see detail in Figure 4 for the construction), of which all parts consist of
stainless steel.
The high-pressure sampling apparatus specified in ISO 6978-1 may also be used by adapting it for two
sampling tubes. The high-pressure apparatus may also be used for sampling at atmospheric pressure.
5.1.2.13 Connections, between the inlet of the vessel and the sampling tubes consisting of a ball socket
with screw cap and dividable screw.
5.2 Desorption station (see Figure 5), comprising the following:
5.2.1 Tube oven, for the thermal desorption of mercury from the quartz glass sampling tubes or quartz
glass analytical tubes.
The length of the heating zone of the oven should be (120 ± 20) mm to cover the part of the tubes filled with
Au/Pt-alloy thread. The inner diameter shall allow the free passage of the tube sockets. The heating capacity
of the oven shall be capable of reaching 800 °C within u 2 min.
5.2.2 Quartz glass analytical tubes (see Figure 3).
5.2.3 Mercury trap (see Figure 5), filled with sulfur impregnated activated charcoal or any other suitable
mercury adsorbent such as gold/platinum alloy.
5.2.4 Air pump, capable of delivering a flow rate between 0,5 l/min and 2 l/min.
5.2.5 Flow meter, for measuring flow rates ranging between 1 l/min and 5 l/min.
5.2.6 Polyvinyl acetate (PVA) tubing, having an internal diameter of 3 mm.
5.3 Cold vapour atomic absorption spectrometer (AAS) or atomic fluorescence spectrometer (AFS).
A cold vapour AAS or an AFS with an integrator and a mercury unit, capable of detecting at least 0,05 ng Hg,
standard laboratory equipment and polyvinyl acetate (PVA) tubing are required. However, hoses of other
suitable plastic material, such as polytetrafluoroethylene (PTFE) or polyamide (PA), may be used.
It is essential to make sure that the flowrate transporting the mercury through the analytical system remains
constant.
5.4 Calibration set (see Figure 6), for the preparation of mercury-saturated air (6.6), consisting of the
elements given in 5.4.1 to 5.4.7.
5.4.1 Bottles, of 500 ml capacity.
5.4.2 Screw caps with polytetrafluoroethylene (PTFE)-coated silicone rubber septa.
5.4.3 PVA tubing.
5.4.4 Stainless steel syringe needles.
5.4.5 Thermometer, with a range from 10 °C to 40 °C and graduated to 0,1 °C.
5.4.6 Insulated box.
5.4.7 Gastight glass syringe, equipped with a PTFE plunger, with a stainless steel needle, capable of
delivering a volume of 0,5 ml to 5 ml.
5.5 Sampling and analytical tubes (see Figure 3).
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
Dimensions in millimetres


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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
Key
1 pressure gauge (0 MPa to 25 MPa) 13 water lock set at 0,4 m water column
2 valve 14 screw cap M20
3 bypass valve 15 ball socket
4 pressure-reducing valve 16 O-ring
5 pressure relief valve set at 10 MPa 17 dividable screw M20 (polytetrafluoroethylene)
6 three-way valve 18 first sampling tube
7 heating tape 19 second sampling tube
8 high-pressure vessel 20 clamp
9 pressure gauge (0 MPa to 10 MPa) 21 connecting piece
10 pressure-reducing valve 22 gaz meter
11 pressure relief valve set at 4 kPa 23 temperature gauge
12 flow indicator 24 pressure gauge

Figure 4 — Sampling apparatus for sampling at high pressure
Dimensions in millimetres

Key
1 air pump 6 tube oven
2 mercury trap 7 temperature gauge
3 flowmeter 8 glass connection tube
4 PVA tubing 9 analytical tube
5 sampling tube 10 glass wool
a
Mercury trap filled with activated charcoal impregnated with sulfur or any other suitable mercury adsorbent.
Figure 5 — Desorption station
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
6 Reagents and materials
Use only reagents and materials which contain negligible amounts of mercury.
6.1 Gold/platinum alloy thread, produced from gold/platinum alloy 80 % to 90 % gold (Au) and the
remainder platinum (Pt) of 0,1 mm diameter and a length of 10 m (to fill one quartz glass tube).
2
Alternatively to gold/platinum alloy thread, silica spherules having a specific surface of about 10 m /g and
impregnated with 3 % Au by mass may be used.
6.2 Metallic mercury, of purity W 99,9 %.
DANGER — Mercury presents a health hazard if incorrectly handled. Avoid inhalation of the vapour.
Spillages of mercury should be removed immediately, including places which are difficult to access.
Use a plastic syringe to draw it up. Smaller quantities can be covered by sulfur powder and removed.
6.3 Solvents methanol and iso-octane.
6.4 Activated charcoal, impregnated with sulfur for air purification or any other suitable mercury adsorbent
such as gold/platinum alloy.
6.5 Sulfur powder, for covering small amounts of spilled mercury.
6.6 Mercury-saturated air (see Figure 6).
Close two bottles (5.4.1), each containing 20 g of metallic mercury (6.2), with screw caps (5.4.2). Using PVA
tubing (5.4.3) attached at both ends to stainless steel syringe needles (5.4.4), connect the bottles together by
inserting the needles through each of the septums (see Figure 6). Keep the first bottle at atmospheric
pressure by inserting another stainless steel syringe needle (5.4.4) through its septum. Equip the second
bottle with a thermometer (5.4.5), not shown in Figure 6. Place the bottles in an insulated box (5.4.6) to
minimize temperature fluctuations. Using a gastight glass syringe (5.4.7), withdraw mercury-saturated air from
the second bottle by inserting the needle through its septum. Allow at least 1 h after set-up for the mercury-
saturated air to reach stable conditions.

Key
1 PVA tubing
2 gastight glass syringe
3 screw cap with PTFE-coated silicone rubber septum
4 stainless steel syringe needles
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SIST EN ISO 6978-2:2005
ISO 6978-2:2003(E)
Figure 6 — Calibration set to be placed in an insulated box
7 Preparation of sampling and analytical tubes
7.1 Filling
Crumple 10 m of gold/platinum alloy thread (6.1) into a ball, then pull it out to form a cylinder so as to fit into
the sampling or analytical tubes (see Figure 3) and part of which sufficiently narrow to pass through the
indentation. Introduce the crumpled thread cylinder into the tube so as to partially pass the indentation
(15 ± 5) mm, then compress the thread to pack the filling of cross-section as shown in Figure 3. This should
result in a filled zone of about (80 ± 5) mm for sampling tubes and about (60 ± 5) mm for analytical tubes.
For gold-impregnated silica, fill the tubes between plugs of glass wool to give a length of the sorption zone of
(10 ± 1) mm.
7.2 Cleaning
Before use, thoroughly clean quartz glass tubes used for sampling and analysis by repeated heating to 800 °C
for several minutes whilst purified air is passed through the tubes.
To check the mercury contamination of the tubes, connect them to the AAS or AFS as described in 7.3. If the
tube contains W 0,1 ng Hg, repeat the cleaning procedure until this level is obtained.
After cleaning and allowing the tubes to cool, seal the tubes immediately with plastic film or clean rubber plugs
and store them in a hermetically closed vessel. It is recommended to use at least one tube as a blank to check
for possible contamination during storage.
7.3 Efficiency testing
Since the efficiency of sampling and analytical tubes can decline with time and/or usage, mercury can pass
through the tube without being sorbed. The efficiency should be checked periodically depending on use,
especially when the Hg concentration is lower than with parallel measurements with other tubes or when the
ratio of Hg found in the first and second tube differs to parallel measurements.
Check the efficiency by connecting a tube to the AAS or AFS and sucking air or inert gas through the tu
...