ASTM D5954-98
(Test Method)Standard Test Method for Mercury Sampling and Measurement in Natural Gas by Atomic Absorption Spectroscopy
Standard Test Method for Mercury Sampling and Measurement in Natural Gas by Atomic Absorption Spectroscopy
SCOPE
1.1 This test method covers the determination of total mercury in natural gas at concentrations down to 0.01 [mu]g/m . It includes separate procedures for both sampling and the atomic absorption spectrophotometric determination of mercury. The procedure detects both inorganic and organic forms of mercury.
1.2 The values stated in SI units are to be regarded as the 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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Designation:D5954–98
Standard Test Method for
Mercury Sampling and Measurement in Natural Gas by
Atomic Absorption Spectroscopy
This standard is issued under the fixed designation D 5954; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This test covers the determination of total mercury in 4.1 This test method can be used to measure the level of
natural gas at concentrations down to 1 ng/m . It includes mercury in natural gas streams for purposes such as determin-
separate procedures for both sampling and atomic absorption ing compliance with regulations, studying the effect of various
spectrophotometric determination of mercury. The procedure abatement procedures on mercury emissions, checking the
detects both inorganic and organic forms of mercury. validity of direct instrumental measurements, and verifying
1.2 The values stated in SI units are to be regarded as the that mercury concentrations are below those required for
standard. natural gas processing and operation.
1.3 This standard does not purport to address all of the 4.2 Adsorption of the mercury on gold-coated beads can
safety concerns, if any, associated with its use. It is the remove interferences associated with the direct measurement
responsibility of the user of this standard to establish appro- of mercury in natural gas. It preconcentrates the mercury
priate safety and health practices and determine the applica- before analysis thereby offering measurement of ultra-low
bility of regulatory limitations prior to use. average concentrations in a natural gas stream over a long span
of time. It avoids the cumbersome use of liquid spargers with
2. Referenced Documents
on-site sampling, and eliminates contamination problems as-
5,6,7
2.1 ASTM Standards: sociated with the use of potassium permanganate solutions.
D 1193 Specification for Reagent Water
5. Apparatus
D 3223 Test Method for Total Mercury in Water
D 3684 Test Method for Total Mercury in Coal by the 5.1 Atomic Absorption Spectrophotometer, equipped with a
Oxygen Bomb Combustion/Atomic Absorption Method 10-cm-long path quartz absorption cell and a mercury source
E 200 Practice for Preparation, Standardization, and Stor- lamp (EDLor other high intensity lamp). It must be capable of
age of Standard and Reagent Solutions for Chemical collecting and integrating data over a 30- to 60-s time window.
Analysis Background capabilities are strongly recommended.
NOTE 1—Detection sensitivity may vary significantly depending on the
3. Summary of Test Method
type of spectrophotometer and its accessories.
3.1 Mercury in a gas stream is adsorbed onto gold-coated
5.2 Rotameter or Other Flow Measurement Device capable
silica beads and subsequently directly desorbed by heat into a
of attaining and regulating air at approximately 500 mL/min.
long path-length quartz cell connected to an atomic absorption
5.3 Rotameter or Other Flow Measurement Device capable
spectrophotometer. Mercury atoms are detected by measuring
of attaining and regulating the natural gas sample at approxi-
their absorbance of light from a mercury source lamp at a
mately 1000 to 2500 mL/min.
characteristic wavelength. The mercury concentration is ob-
5.4 Dry or Wet Positive Displacement Test Meter, or other
tained from the absorbance peak area by comparison to
calibrated total flow measurement device for measuring the
standards prepared at the time of analysis.
volume of the sample.
This test method is under the jurisdiction ofASTM Committee D-3 on Gaseous
Fuels and is the direct responsibility of Subcommittee D03.05 on Determination of Schroeder,W.H.,“SamplingandAnalysisofMercuryanditsCompoundsinthe
Special Constituents of Gaseous Fuels. Atmosphere,” Environmental Science & Technology, 16, 1982, 394A–399A.
Current edition approved May 10, 1998. Published March 1999. Originally Chao, S.S., andAttari,A., “Characterization and Measurements of Natural Gas
published as D 5954–96. Last previous edition D 5954–96. Trace Constituents—Volume II: Survey,” Final Report GRI-94/0243.2, June 1994.
2 7
Annual Book of ASTM Standards, Vol 11.01. Braman, R.S., and Johnson, D.L., “Selective Absorption Tubes and Emission
Annual Book of ASTM Standards, Vol 05.05. Technique for the Determination of Ambient Forms of Mercury in Air,” Environ-
Annual Book of ASTM Standards, Vol 15.05. mental Science & Technology, 8, 1974, pp. 996–1003.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5954
5.5 TFE-Fluorocarbon Tubing, to make connections to the where such specifications are available. Other grades may be
atomic absorption spectrophotometer. The size should be used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the
appropriate for the quartz absorption cell.
1 accuracy of the determination.
5.6 Quartz Tubing, 12 cm long, ⁄4-in. outside diameter, to
6.2 Reagent Water—Reagent water, conforming to Type II
be used for sorbent (gold-coated silica) packing.
of Specification D 1193, shall be used for preparation of
NOTE 2—All glass and plastic ware coming into contact with the
reagents and washing of the quartz tubing.
sample must be acid washed with 20 % nitric acid and thoroughly rinsed
6.3 Gold Chloride—Dissolve2gof gold chloride
with water.
(HAuCl ·3H O)inapproximately10mLofwater(Warning—
4 2
Poison).
5.7 Quartz Tubing, approximately 24 in. long and 1-in.
6.4 Sulfuric Acid, (concentrated, H SO , relative density
outside diameter, to be used for the preparation of the gold- 2 4
1.84) (Warning—Poison).
coated silica.
6.5 Nitric Acid, (concentrated, HNO , relative density 1.42)
5.8 Quartz Wool to be used for sorbent (gold-coated silica)
(Warning—Poison).
packing.
6.6 Nitric Acid, (20 %)—Mix 1 volume of concentrated
5.9 Fused Silica or Quartz Beads, 60/80 mesh, to be used
nitric acid with 4 volumes of water.
for the preparation of the gold-coated silica.
6.7 Mercury, triple distilled (Warning—Poison).
5.10 Tube Furnace, approximately 8 to 10 cm in length, to
6.8 Mercury Standard Stock Solution, (1000 µg/mL)—
be used for the preparation of the gold-coated silica and the
Dissolve 1.080 g of mercury (II) oxide (HgO) in a minimal
mercury desorption. It must be capable of maintaining tem-
amount of HCl (1 + 1). Dilute to 1 L with water.
peratures up to 750 6 25°C over a 4-cm length. A Variac or
6.9 Mercury Standard Intermediate Solution, (10 µg/mL)—
other temperature control device may be required.
Add 10.00 mL of the mercury standard stock solution to
approximately 500 mL of water. Add 0.5 mL of concentrated
NOTE 3—A shorter sampling tube and a shorter tube furnace may be
nitric acid and dilute to 1 L with water. Prepare this standard
used as long as the specified temperature can be maintained.
solution daily.
5.11 Silicone Tubing, ⁄4-in. inside diameter for connections.
6.10 Mercury Standard Working Solution, (100 ng/mL)—
1 1
5.12 Stainless Steel Tubing, ⁄4- and ⁄8-in outside diameter,
Add 1.00 mL of the mercury standard intermediate solution to
various lengths, for connections. approximately 50 mL of water. Add 0.05 mL of concentrated
nitric acid and dilute to 100 mL with water. If micropipets are
5.13 Gastight Tube Fittings, ⁄4-in. nylon or TFE-
not available, this standard may be prepared by serial dilution
fluorocarbon construction, gastight end-cap type, plus one
of the mercury standard intermediate solution. Prepare this
stainless steel “T” fitting.
standard solution daily.
5.14 Precision Gastight Syringe, 500 µL, equipped with a
6.11 Air, PP grade, or carbon filtered.
needle with a side port opening.
6.12 Hydrogen, PP grade (Warning—Flammable).
NOTE 4—A digital syringe is recommended for better accuracy and 6.13 Nitrogen, PP grade.
precision in calibration.
6.14 Sulfur Impregnated Carbon, used to filter carrier
gases.
5.15 Septum Material, GC grade, low bleed type, made
from silicone.
7. Procedure for the Preparation of the Gold-Coated
5.16 Water Bath or Constant Temperature Apparatus, ca-
Beads
pable of regulating a sealed vial of mercury to 26 6 0.05°C.
7.1 Soak the silica beads in concentrated sulfuric acid
5.17 Sealed Vial of Mercury, prepared from a 250-mL glass
overnighttoremoveanycoatingorcontamination.Silicabeads
bottle with a TFE-fluorocarbon septum cap and triple distilled
used for GC operations are often deactivated by silanization
elemental mercury.
and this coating must be removed. Wash thoroughly with
5.18 Thermocouple, for monitoring tube furnace tempera-
reagent water and dry.
tures.
7.2 Add 50 g of acid washed silica beads to 10 mL of gold
5.19 Heating Tape, capable of maintaining a temperature of
chloride solution. This will result in a 2 % loading of gold on
50 to 60°C, to heat trace tubing from the outlet end of the the silica substrate. Add a minimal amount of water, if
sampling tube to the inlet port of the AAS cell. A Variac or necessary, to form a slurry. Heat on a hot plate with stirring
other temperature control device may be required. until most of the water evaporates. Let the beads air-dry until
5.20 StainlessSteel6-PortSwitchingValve, ⁄8in.forcarrier
gas control (optional).
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
6. Reagents
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
6.1 Purity of Reagents—Reagent grade chemicals shall be
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
used in all tests. Unless otherwise indicated, it is intended that
MD.
all reagents shall conform to the specifications of the Commit-
HGR carbon available from Calgon Carbon Corp., Western Region, 2750-C
tee onAnalytical Reagents of theAmerican Chemical Society, Goodrick Ave., Richmond, CA 94801.
D5954
the apparent moisture is evaporated. The color may change system must be passivated with the sample gas before any
from yellow to a yellowish orange. sampling, especially if low levels of mercury are expected.
7.3 Pack the coated beads into the 1-in. outside diameter Stainlesssteeltubingmustbeusedforconnectionsupstreamof
quartz tube with quartz wool plugs at either end and begin the pressure regulator. High density TFE-fluorocarbon or
heating using a tube furnace with a nitrogen purge. Slowly stainless steel tubing is preferred for connections downstream
raisethetemperaturefromambientto170°Ctodrythoroughly. of the regulator. Flexible silicone tubing may be used to make
A heat gun may be used to remove condensed moisture short connections to sampling tubes. Any pumps, metering
downstream of the furnace. The color of the beads will begin valves, and so forth or other flow- and pressure-controlling
to turn orange and then purplish. This may take 1 to2hto devices should be located downstream of the sampler if
complete depending on how much moisture is present. possible. The entire sampling line should be heated to prevent
condensation, especially when a pressure reduction device is
NOTE 5—Caution: Moisture and oxygen must be removed and the
used to step down the pressure for sampling.
beads completely dry before hydrogen gas is introduced.
9.3 Ascertain that the sample can be obtained at a pressure
7.4 Switch the gas to hydrogen and slowly raise the tem-
not exceeding 15 psig (10 psig is preferable) and a flow of 1 to
perature to 250°C to reduce the gold ion to metallic gold. As
2.5 L/min (2 L/min is preferable). Pressure- and flow-control
the temperature rises, HCl vapors are generated from the tube
devices may be required. A total flow volume measurement
and may appear as a smoky haze. A yellowish haze may be
device, such as a dry test meter, can be used to record the exact
seen on the inside walls of the quartz tube. The reaction is
amounts of gas sampled for more accurate sampling.
complete when this haze either disappears or does not change
9.4 Using a calibrated rotameter, installed upstream of the
over a 15- to 20-min period. Do not allow the temperature of
total flow measurement device, determine an approximate flow
the furnace to rise above 250°C since gold chloride will
control setting for the selected flow at the applied pressure.
sublimate at 265°C. This procedure may take 2 to3hto
Thiswillsavetimewhensettingupthesamplingtubesandwill
complete.
condition the sampling system.
9.5 Remove the fitting on one end of each tube and join the
NOTE 6—Caution: Thegasstreamexitingfromthetubefurnaceshould
be directed into a flask containing water to absorb the HCl gas generated
two tubes end-to-end with a short piece of silicone tubing.
as the gold ion is reduced.
9.6 Connect the back end of the sampling tube assembly
(Tube 2) to the rotameter and connect the front end of the
7.5 Raise the furnace temperature to approximately 400°C
sampling tube assembly (Tube 1) to the sampling point.
over a 10-min period. Switch the gas to nitrogen and continue
Carefully open the sampling valve and quickly adjust the flow
heating up to 500 to 550°C for an additional 10 min. Remove
control (and pressure if necessary) to obtain the required
the quartz tube from the furnace and allow to cool under the
flowrate.Recordthetimeandflowdataatthestartofsampling.
nitrogen purge.
Mark the direction the sample gas flowed through the tube.
8. Procedure for the Preparation of the Sampling Tubes
9.7 Flow the sample through the sampling tube for the
8.1 Washeach ⁄4-in.outsidediameterquartztubewith20 % desired amount of time, periodically checking that the flow is
HNO , rinse with water, and dry in an oven at 105°C. staying close to what it originally was and adjusting it if
8.2 Place a 1-cm length of quartz wool at one end of a tube. necessary. Typical volumes of gas range from 50 to 100 L. A
8.3 Add 0.5 g of the gold-coated beads to a quartz tube smaller volume of gas should be used for a sample containing
(oriented vertically) and gently tap the contents to eliminate air a high concentration of mercury.The optimal range that should
spaces. The final length of gold-coated beads should be be collected is between 2 and 300 ng of mercury. The capacity
approximately 2.5 cm and centered within the tube. of the sorbent is much higher, approximately 7 µg, but a
8.4 Add a final 1-cm length of quartz wool to the opposite loading at this level should be avoided as th
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