ASTM D6350-98
(Test Method)Standard Test Method for Mercury Sampling and Analysis in Natural Gas by Atomic Fluorescence Spectroscopy
Standard Test Method for Mercury Sampling and Analysis in Natural Gas by Atomic Fluorescence Spectroscopy
SCOPE
1.1 This test method covers the determination of total mercury in natural gas streams down to 0.001 ug/m3. It includes procedures to both obtaining a representative sample and the atomic fluorescence detection of the analyte. This procedure can be applied for both organic and inorganic mercury compounds.
1.2 Both, inch-pound and SI (metric) units of measurement are used throughout this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
Designation:D6350–98
Standard Test Method for
Mercury Sampling and Analysis in Natural Gas by Atomic
Fluorescence Spectroscopy
This standard is issued under the fixed designation D6350; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (ϵ) indicates an editorial change since the last revision or reapproval.
1. Scope fluorescencewhichreradiatesattheexcitationwavelength.The
fluorescenceradiationisdetectedbyaphotomultipliertubeand
1.1 This test method covers the determination of total
is directly proportional to the amount of mercury in the cell.
mercury in natural gas streams down to 0.001 µg/m.It
The concentration of the element in the original sample is
includes procedures to both obtaining a representative sample
obtained by comparison to freshly prepared standards, which
and the atomic fluorescence detection of the analyte. This
are analyzed by direct injection of mercury vapor into the
procedure can be applied for both organic and inorganic
instrument at a specified temperature on supported gold traps.
mercury compounds.
1.2 Both, inch-pound and SI (metric) units of measurement
4. Significance and Use
are used throughout this standard.
4.1 This test method can be used to determine the total
1.3 This standard does not purport to address all of the
mercury concentration of a natural gas stream down to 0.001
safety concerns, if any, associated with its use. It is the
µg/m . It can be used to assess compliance with environmental
responsibility of the user of this standard to establish appro-
regulations, predict possible damage to gas plant equipment,
priate safety and health practices and determine the applica-
and monitor the efficiency of mercury removal beds.
bility of regulatory limitations prior to its use.
4.2 The preferred sampling method for mercury collection
2. Referenced Documents is on supported gold sorbent, which allows the element to be
trapped and extracted from the interfering matrix of the gas.
2.1 ASTM Standards:
Thermal desorption of mercury is performed by raising the
D3684 Test Method for Total Mercury in Coal by the
temperature of the trap by means of a nichrome wire coiled
Oxygen Bomb Combustion Atomic Method
around it.
D5954 Test Method for Mercury Sampling and Measure-
4.3 Since AFS demonstrates lower detection limits ap-
ment in Natural Gas
proaching0.1pg,thistestmethodavoidsdifficultiesassociated
2.2 ISO Standard:
with prolonged sampling time. Saturation of the trap with
ISO6978 Determination of Mercury in Natural Gas
interferantssuchashydrogensulfide(H S)isavoided.Average
3. Summary of Test Method
sampling can range between 15 to 30 min, or less.
3.1 Mercury from the gaseous stream is absorbed and
5. Apparatus and Materials
preconcentrated onto a gold-coated silica sand trap. The
5.1 Sampling Equipment:
analyte is desorbed by raising the temperature of the trap, and
5.1.1 Sample probe, equipped with a ball valve of the Type
a flow of inert gas carries the mercury atoms into the cell
316 SS, connected to the sampling point is highly recom-
assembly of an atomic fluorescence spectrophotometer. The
mended.
cell is irradiated by a low pressure mercury vapor lamp at
5.1.2 Pressure regulation devices, such as two-stage stain-
253.652 nm. Excitation of mercury atoms produces resonance
less steel pressure regulator, capable of reducing the pressure
from 2000 to 30 psi.
5.1.3 On/off and micrometric-type valves capable of regu-
This test method is under the jurisdiction of ASTM Committee D-03 on
lating the natural gas sample flow rate in the range of 100 to
Gaseous Fuels and is the direct responsibility of Subcommittee D03.05 on
200 mL/min.
Determination of Special Constituents of Gaseous Fuels.
Current edition approved Nov. 10, 1998. Published March 1999. Originally
5.1.4 Stainlesssteeltubingandcompression-typefittings,as
published as D6350-98.
required.
Annual Book of ASTM Standards, Vol 05.05
3 5.1.5 Dry or wet flow meter or integrating anemometer to
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor New York, NY 10036. measure properly the total volume of the gas sample collected.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D6350–98
5.1.6 Gold-coated fused silica sand traps. mercury trapping. Sampling will require the use of specific
procedures; consult appropriate regulations.
NOTE 1—For details on trap preparation refer to Test Method
7.2 Sampling arrangements will always use a minimum of
D5954D5954, the procedure of vapor deposition used in scanning
two sampling gold tubes per location. The recommended
electron microscopy (SEM) techniques, and, ISO6978, 1993.
sampling setup is shown schematically in Fig. 1.
5.2 Analytical Equipment:
7.3 Assemblethepartswithoutconnectingthegoldtraps,as
5.2.1 Atomic Fluorescence Spectrophotometer, equipped
depicted in Fig. 1. Open the flow of gas from the main valve
with a quartz cell and a mercury lamp capable of irradiating at
andregulatethepressuredownto30psi.Opentheon/offvalve
253.652-nm wavelength.
and set an approximate flow of 150 mL/min with the micro-
5.2.2 Chromatography Grade Teflont and Silicon Tubing,
metric valve adjustment. Check the flow with a dry or bubble
forconnectionsbetweenthethermaldesorptionsystemandthe
flowmeter.Letthesystempurgeforatleast30min.Purgingis
AFS. Length, ID, and OD are selected as appropriate.
necessary, especially if the pressure regulator, tubing, and
5.2.3 Nichrome Wire (22 gauge) coiled (20 turns/inch)
valveswereusedatapreviouslocation.Thelongerthepurging
around the traps for the thermal desorption of mercury.
period the better.
5.2.4 Variable Voltage Regulator, (rheostat) used in con-
7.4 When purging is completed, close the on/off valve and
junction with the nichrome wire for the rapid heating of the
connect both gold traps to the system. Use Tygon tubing or
traps.
similar to connect traps together.
5.2.5 Temperature-Resistant Rubber Tubing,of ⁄4 in. (0.06
7.5 Open the on/off valve again and record the time and the
mm),connectingthetraptothetemperaturedesorptionsystem.
exact flow through the traps. Periodically check, every 15 min,
5.2.6 GC-Grade Septa, low bleed, made of silicone used in
that the flow remains constant throughout the duration of
the injection port and mercury-sealed vial.
sampling. Best results are obtained with a 100- to 200-mL/min
5.2.7 Constant Temperature Bath, capable of regulating the
flowrateandanaveragesamplingtimeof15to30min.Record
temperature of a sealed vial of mercury to 25 6 0.1°C.
both readings.
5.2.8 Various Stainless Steel “T” Fittings.
7.6 When sampling time has elapsed, close the on/off valve
5.2.9 Gastight Syringes, fixed or variable volume, in the
and disconnect the traps. Carefully cap and label them accord-
range of 10 to 500 µL.
ingly(Tube1andTube2).Accuratelyrecordthefinaltimeand
5.2.10 A Glass Vial,100mLfittedwithaseptumtoperform
flow data for later calculations.
as mercury container.
5.2.11 Chart Recorder, or integrator to process a hard copy
8. Calibration of the Instrument (Gaseous Standard)
of the data acquired by the detector.
8.1 Calibration according to the following procedure is
NOTE 2—Commercially available permeation injection sources, based recommended since it is easy to perform and results in
on the principle of permeation tubes, can be used instead of gastight
repeatability not exceeding a 10% range between duplicate
syringes. Permation devices can be used in lieu of gastight syringe-based 5
analyses. (see Footnote 5 and ISO6978).
sample introduction.Apermiation system can automatically introduce an
8.2 Standardsarepreparedbyinjectionofdifferentvolumes
accurately known amount of mercury vapor onto a gold trap. This is
of the head space from a thermostatted sealed mercury vial.
particularly convenient for quantifying low pg amounts of mercury.
Injectionofthealiquots,usuallyinthemicrolitrerange,should
6. Reagents
be made directly onto a mercury trapping tube, using aT-piece
injection port and argon gas as carrier. See Fig. 2 for details.
6.1 Because of the error and contamination that may be
8.3 All surfaces coming in contact with the mercury vapor
introduced from impurities in the chemicals, the use of high
should be passivated (except the analytical trap) before actual
purity reagents is strongly recommended.
readings can be taken. Condition all tubing, instrument con-
6.1.1 Mercury Analytical Grade, triple distilled.
nections, as well as all syringes, by multiple injections of the
NOTE 3—Warning:Mercury vapor is harmful. Use proper ventilation
gaseous mercury vapor head space contained in the
when handling.
temperature-controlled mercury vial.
6.2 Argon Gas, ultra high purity grade (UHP 99.999%).
8.4 The concentration of a particular aliquot, taken with a
gastightsyringe,canbecalculatedbythefollowingequationof
NOTE 4—For the permeation injection source procedure, certified
state of real gases:
mercury permeation tubes are commercially available. Tubes can also be
prepared and calibrated by comparison to syringe injection or by weight
log~ng/mL! 5 ~23104/K! 111.709 (1)
loss,overtime,usingananalyticalbalancewitharesolutionof 60.01mg.
where:
7. Sampling Procedure
K =
...
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