1、Designation: D6350 14Standard Test Method forMercury Sampling and Analysis in Natural Gas by AtomicFluorescence Spectroscopy1This standard is issued under the fixed designation D6350; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of totalmercury in natural gas streams down to 0.001 g/m3.Itinc
3、ludes procedures to both obtaining a representative sampleand the atomic fluorescence detection of the analyte. Thisprocedure can be applied for both organic and inorganicmercury compounds.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in
4、thisstandard.1.2.1 Exception: Inch-pound units are used in Sections 5.1.2and 7.3 when discussing pressure regulator usage.1.3 Warning: Mercury has been designated by many regu-latory agencies as a hazardous material that can cause seriousmedical issues. Mercury, or its vapor, has been demonstrated t
5、obe hazardous to health and corrosive to materials. Cautionshould be taken when handling mercury and mercury contain-ing products. See the applicable product Safety Data Sheet(SDS) for additional information. Users should be aware thatselling mercury and/or mercury containing products into yourstate
6、 or country may be prohibited by law.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory lim
7、itations prior to its use.2. Referenced Documents2.1 ASTM Standards:2D5954 Test Method for Mercury Sampling and Measure-ment in Natural Gas by Atomic Absorption Spectroscopy2.2 ISO Standard3ISO 6978 Determination of Mercury in Natural Gas3. Summary of Test Method3.1 Mercury from the gaseous stream i
8、s absorbed andpreconcentrated onto a gold-coated silica sand trap. Theanalyte is desorbed by raising the temperature of the trap, anda flow of inert gas carries the mercury atoms into the cellassembly of an atomic fluorescence spectrophotometer. Thecell is irradiated by a low pressure mercury vapor
9、lamp at253.652 nm. Excitation of mercury atoms produces resonancefluorescence which reradiates at the excitation wavelength. Thefluorescence radiation is detected by a photomultiplier tube andis directly proportional to the amount of mercury in the cell.The concentration of the element in the origin
10、al sample isobtained by comparison to freshly prepared standards, whichare analyzed by direct injection of mercury vapor into theinstrument at a specified temperature on supported gold traps.4. Significance and Use4.1 This test method can be used to determine the totalmercury concentration of a natu
11、ral gas stream down to 0.001g/m3. It can be used to assess compliance with environmentalregulations, predict possible damage to gas plant equipment,and monitor the efficiency of mercury removal beds.Where L1and L2are the specimen lengths at temperatures T1and T2, respectively. is, therefore, obtaine
12、d by dividing thelinear expansion per unit length by the change in temperature.4.2 The preferred sampling method for mercury collectionis on supported gold sorbent, which allows the element to betrapped and extracted from the interfering matrix of the gas.Thermal desorption of mercury is performed b
13、y raising thetemperature of the trap by means of a nichrome wire coiledaround it.4.3 The preferred sampling method for mercury collectionis on supported gold sorbent, which allows the element to betrapped and extracted from the interfering matrix of the gas.1This test method is under the jurisdictio
14、n ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.05 on Determination ofSpecial Constituents of Gaseous Fuels.Current edition approved Feb. 1, 2014. Published February 2014. Originallyapproved in 1998. Last previous edition approved in 2003 as D6350 - 98(200
15、3),which was withdrawn in July 2012 and reinstated February 2014. DOI: 10.1520/D6350-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summa
16、ry page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Thermal desorption of mercury is
17、 performed by raising thetemperature of the trap by means of a nichrome wire coiledaround it.4.4 Since AFS demonstrates lower detection limits ap-proaching 0.1 pg, this test method avoids difficulties associatedwith prolonged sampling time. Saturation of the trap withinterferants such as hydrogen su
18、lfide (H2S) is avoided.Averagesampling can range between 15 to 30 min, or less.5. Apparatus and Materials5.1 Sampling Equipment:5.1.1 Sample probe, equipped with a ball valve of the Type316 SS, connected to the sampling point is highly recom-mended.5.1.2 Pressure regulation devices, such as two-stag
19、e stain-less steel pressure regulator, capable of reducing the pressurefrom 2000 to 30 psi.5.1.3 On/off and micrometric-type valves capable of regu-lating the natural gas sample flow rate in the range of 100 to200 mL/min.5.1.4 Stainless steel tubing and compression-type fittings, asrequired.5.1.5 Dr
20、y or wet flow meter or integrating anemometer tomeasure properly the total volume of the gas sample collected.5.1.6 Gold-coated fused silica sand traps.NOTE 1For details on trap preparation refer to Test Method D5954,the procedure of vapor deposition used in scanning electron microscopy(SEM) techniq
21、ues, Fitzgerald and Gill4, and ISO 6978, 1993.5.2 Analytical Equipment:5.2.1 Atomic Fluorescence Spectrophotometer, equippedwith a quartz cell and a mercury lamp capable of irradiating at253.652-nm wavelength.5.2.2 Chromatography Grade Teflon and Silicon Tubing,for connections between the thermal de
22、sorption system and theAFS. Length, ID, and OD are selected as appropriate.5.2.3 Nichrome Wire (22 gauge) coiled (20 turns/inch)around the traps for the thermal desorption of mercury.5.2.4 Variable Voltage Regulator, (rheostat) used in con-junction with the nichrome wire for the rapid heating of the
23、traps.5.2.5 Temperature-Resistant Rubber Tubing, of14 in. (0.06mm), connecting the trap to the temperature desorption system.5.2.6 GC-Grade Septa, low bleed, made of silicone used inthe injection port and mercury-sealed vial.5.2.7 Constant Temperature Bath, capable of regulating thetemperature of a
24、sealed vial of mercury to 25 6 0.1C.5.2.8 Various Stainless Steel “T” Fittings.5.2.9 Gastight Syringes, fixed or variable volume, in therange of 10 to 500 L.5.2.10 A Glass Vial, 100 mL fitted with a septum to performas mercury container.5.2.11 Chart Recorder, or integrator to process a hard copyof t
25、he data acquired by the detector.NOTE 2Commercially available permeation injection sources, basedon the principle of permeation tubes, can be used instead of gastightsyringes. Permation devices can be used in lieu of gastight syringe-basedsample introduction. A permiation system can automatically in
26、troduce anaccurately known amount of mercury vapor onto a gold trap. This isparticularly convenient for quantifying low pg amounts of mercury.6. Reagents and Materials6.1 Because of the error and contamination that may beintroduced from impurities in the chemicals, the use of highpurity reagents is
27、strongly recommended.6.1.1 Mercury Analytical Grade, triple distilled.NOTE 3Warning: Mercury vapor is harmful. Use proper ventilationwhen handling.6.2 Argon Gas, ultra high purity grade (UHP 99.999 %).NOTE 4For the permeation injection source procedure, certifiedmercury permeation tubes are commerci
28、ally available. Tubes can also beprepared and calibrated by comparison to syringe injection or by weightloss, over time, using an analytical balance with a resolution of 60.01 mg.7. Sampling Procedure7.1 Every effort should be made to ensure that the sample isrepresentative of the gas source from wh
29、ich it is taken. Selectalways the best and more representative sampling point formercury trapping. Sampling will require the use of specificprocedures; consult appropriate regulations.7.2 Sampling arrangements will always use a minimum oftwo sampling gold tubes per location. The recommendedsampling
30、setup is shown schematically in Fig. 1.7.3 Assemble the parts without connecting the gold traps, asdepicted in Fig. 1. Open the flow of gas from the main valveand regulate the pressure down to 30 psi. Open the on/off valveand set an approximate flow of 150 mL/min with the micro-metric valve adjustme
31、nt. Check the flow with a dry or bubbleflow meter. Let the system purge for at least 30 min. Purging isnecessary, especially if the pressure regulator, tubing, andvalves were used at a previous location. The longer the purgingperiod the better.7.4 When purging is completed, close the on/off valve an
32、dconnect both gold traps to the system. Use Tygon tubing orsimilar to connect traps together.7.5 Open the on/off valve again and record the time and theexact flow through the traps. Periodically check, every 15 min,that the flow remains constant throughout the duration ofsampling. Best results are o
33、btained with a 100- to 200-mL/minflow rate and an average sampling time of 15 to 30 min. Recordboth readings.7.6 When sampling time has elapsed, close the on/off valveand disconnect the traps. Carefully cap and label them accord-ingly (Tube 1 and Tube 2).Accurately record the final time andflow data
34、 for later calculations.8. Calibration of the Instrument (Gaseous Standard)8.1 Calibration according to the following procedure isrecommended since it is easy to perform and results in4Fitzgerald, W.F., and Gill, G.A. “Subnanogram Determination of Mercury byTwo-Stage Gold Amalgamation and Gas Phase
35、Detection Applied to AtmosphericAnalysis,” Analytical Chemistry, 11, 1714, 1979.D6350 142repeatability not exceeding a 10 % range between duplicateanalyses. (see Dumarey, Temmerman, Dams, and Hoste5andISO 6978).8.2 Standards are prepared by injection of different volumesof the head space from a ther
36、mostatted sealed mercury vial.Injection of the aliquots, usually in the microlitre range, shouldbe made directly onto a mercury trapping tube, using a T-pieceinjection port and argon gas as carrier. See Fig. 2 for details.8.3 All surfaces coming in contact with the mercury vaporshould be passivated
37、(except the analytical trap) before actualreadings can be taken. Condition all tubing, instrumentconnections, as well as all syringes, by multiple injections ofthe gaseous mercury vapor head space contained in thetemperature-controlled mercury vial.8.4 The concentration of a particular aliquot, take
38、n with agastight syringe, can be calculated by the following equation ofstate of real gases:logng. mL! 5 2 3104 K! 1 11.709 (1)where:K = Mercury temperature in Kelvins.For instance, a 100-L withdrawal of the head space overmercury at 24C will result in an absolute mercury concentra-tion of 1.83 ng o
39、n the gold trap.8.5 The analytical system should be assembled using mini-mal length of high density Teflon tubing. The carrier gas flowshould be carefully controlled using a rotameter, mass flowcontroller, or other equivalent device at 100 to 150 mL/min(see Fig. 2 and Fig. 3).8.6 After injection of
40、the standard, allow 2 min to elapsebefore starting the heating cycle. Continuously flow argonthrough the trap during this waiting period to establish a flatbaseline.8.7 Start the heating cycle by turning on the voltageregulator. The nichrome wire will start to heat rapidly. Whenproperly adjusted, it
41、 can reach 550C in less than 40 s withoutthe risk of burning the heater wire.8.8 A chart recorder, integrator, or computer (with appro-priate peak processing software) must be connected at all timesto the signal output of the fluorescence detector to obtain a hardcopy of peak (see Fig. 2 and Fig. 3)
42、.NOTE 5The temperature of the mercury vial must be kept at a value5Dumarey, R., Temmerman, E., Dams, R., and Hoste, J., “The Accuracy of theVapour-Injection Calibration Method for the Determination of Mercury byAmalgamation/Cold-Vapor Atomic Absorption Spectrometry,” Analytica ChimicaActa, 170, (198
43、5), pp. 341-346.FIG. 1 Diagram of Sampling Arrangement with Gold-Coated Silica Sand Traps InstallationD6350 143of 25 6 0.1C with the use of a thermostatic bath and a certified NISTtraceable thermometer. The vapor pressure of mercury is significantlyimpacted by small temperature changes. Therefore, s
44、ufficient thermalreequilibration time is required between headspace samplings.9. Analytical Procedure9.1 For sample analysis, connect the field trap on theanalysis train as decipted in Fig. 2. Argon must flow throughthe trap into the detector inlet. Field traps must be connected tothe system in the
45、reverse direction of flow used in sampling thenatural gas stream.9.2 The trap must pass through the coiled nichrome wire, foreasy in-and-out installation procedure. The coil has to fitaround the trap tight enough to provide sufficient contact foracceptable heat transfer, but leave enough room for th
46、e trap toslide in and out with ease.9.3 Set the appropriate parameters in the detector unit andon the integrator system, such as threshold, peak width, areareject, and other parameters.9.4 Start the integrator and wait for at least 30 s, baselineshould be straight and present low noise levels (noise
47、 must notexceed13 the signal expected for 1-pg standard). Turn on thevoltage regulator; a minimum temperature of 550C must beachieved in 40 to 50 s. Absorbed mercury will evolve from thetrap and be detected.An integrator, chart recorder, or computersoftware will record the detector response. Under a
48、ppropriateconditions and normal concentrations, typical peaks will span20 to 50 s.9.5 Leave the heating filament hot for a few more seconds toensure that all the mercury has evolve from the trap. Turn thevoltage regulator and the integrator off. With an auxiliary airline rapidly cool the outside sur
49、face of the trap and filament.Remove the analyzed tube (which is now clean and free frommercury) and repeat Steps 1 through 5 on the remaining sampletube traps.9.6 As part of the QA/QC program recommended for thismethod, a standard is introduced onto a trap used for sampleanalysis. After recovering mercury from a trap, a knownamount of mercury vapor is introduced onto the trap anddesorbed into the analytic system. Percent recoveries arecalculated based upon the amount of mercury introduced ontothe trap and the amount determined by this method. Anacceptable re
