1、Designation: D 3609 00 (Reapproved 2005)Standard Practice forCalibration Techniques Using Permeation Tubes1This standard is issued under the fixed designation D 3609; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes a means for using permeationtubes for dynamically calibrating instruments, analyzers, andanalytic
3、al procedures used in measuring concentrations ofgases or vapors in atmospheres (1,2).21.2 Typical materials that may be sealed in permeation tubesinclude: sulfur dioxide, nitrogen dioxide, hydrogen sulfide,chlorine, ammonia, propane, and butane (1).1.3 The values stated in SI units are to be regard
4、ed asstandard.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 limitations prior to use.2
5、. Referenced Documents2.1 ASTM Standards:3D 1356 Terminology Relating to Sampling and Analysis ofAtmospheresD 3195 Practice for Rotameter CalibrationE 1 Specification for ASTM Liquid-in-Glass Thermometers3. Terminology3.1 DefinitionsFor definitions of terms used in thismethod, refer to Terminology D
6、 1356.4. Summary of Practice4.1 A liquefiable gas, when enclosed in an inert plastic tube,escapes by permeating the tubing wall at a constant, reproduc-ible, temperature-dependent rate.4.2 Permeation tubes are calibrated gravimetrically, with theweight loss of the tube equated to the weight of the e
7、scapingmaterial.4.3 Permeation tubes are held at constant temperature in acarrier-gas stream of dry air or nitrogen to produce a gasconcentration dependent on the permeation rate and the flow ofthe carrier gas.5. Significance and Use5.1 Most analytical methods used in air pollutant measure-ments are
8、 comparative in nature and require calibration orstandardization, or both, often with known blends of the gas ofinterest. Since many of the important air pollutants are reactiveand unstable, it is difficult to store them as standard mixtures ofknown concentration for extended calibration purposes. A
9、nalternative is to prepare dynamically standard blends as re-quired. This procedure is simplified if a constant source of thegas of interest can be provided. Permeation tubes provide thisconstant source, if properly calibrated and if maintained atconstant temperature. Permeation tubes have been spec
10、ified asreference calibration sources, for certain analytical procedures,by the Environmental Protection Agency (3).6. Interferences and Precautions6.1 Permeation tubes are essentially devices to provide aconstant rate of emission of a specific gaseous substance overperiod of time. They consist of a
11、 two-phase (gas-liquid) systemto maintain a constant vapor pressure (at constant temperature)which is the driving force for emission of the gas through asemipermeable membrane (tube walls). They can be expectedto maintain a constant emission rate that is temperaturedependent as long as a significant
12、 amount of liquid is presentin the device. The liquid shall be pure, else its composition maychange during the life time of the tube, due to differentialevaporation, with consequent vapor pressure changes. Caremust also be exercised that the diffusion membrane (tubewalls) is not damaged or altered d
13、uring use. The contents ofpermeation tubes are under relatively high pressure. Accord-ingly, there is the possibility of violent rupture of tube wallsunder high temperature exposure. Permeation rates have tem-perature coefficients up to 10 % per degree Celsius. Whentemperature coefficients are large
14、, above 3 % per degree1This practice is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.01 on Quality Control.Current edition approved Oct. 1, 2005. Published January 2006. Originallyapproved in 1977. Last previous edition approved in 2
15、000 as D 3609 - 00.2The boldface numbers in parentheses refer to references appended to thisstandard.3For 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 D
16、ocument Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Celsius, stringent temperature control is required. Furthermorepermeation tubes exhibit temperature hysteresis so that theymust be temperature eq
17、uilibrated from 2 to 24 h before use,depending upon the temperature differential between storageand use (4). It is important that permeation tubes are filled withanhydrous constituents of high purity. They shall be handledwith care to minimize contact with moisture, oil, and foreignsubstances.6.2 Su
18、lfur dioxide (SO2) permeation tubes are relativelyinsensitive to interferences.6.3 Nitrogen dioxide (NO2) permeation tubes are sensitiveto moisture, hence they should be stored in dry atmospheresand used with relatively dry carrier gases (10 % relativehumidity). Permeation of moisture into the conte
19、nts of a tubemay damage the walls and also cause progressive decreases inthe permeation rate. Moisture incorporated in the contentsduring manufacture can cause the same effect (4).6.4 Hydrogen sulfide (H2S) permeation tubes may turnwhite during use in the presence of oxygen because of inversepermeat
20、ion and formation of collodial sulfur. This phenom-enon may affect the permeation rate, if severe, hence is areason for recalibration. However, in an inert gas stream, thetubes are relatively stable.6.5 Materials of construction shall be compatible with thecontents of the tube. For instance, some fl
21、uorocarbons maycause FEP tubes to swell and possibly to rupture.7. Apparatus7.1 Permeation Tube sized in accordance with and cali-brated to concentrations needed or expected for the analysismethod. The user should check calibration as described inSection 9.1.7.2 Flow and Temperature Control SystemPr
22、epare orpurchase a system that will dry the carrier gas, and control andmeasure its flow as it passes over the permeation tube that isbeing held at constant temperature. If lower concentrations aredesired, a second gas supply (diluent gas) with its control andmeasurement devices may be needed to mix
23、 with the gas fromthe permeation tube chamber. Equipment of this kind isavailable commercially. A typical system contains a thermo-electrically temperature-controlled permeation tube chamberwith temperature control within 60.1C over the range from15 to 35C. Such equipment is well suited to field usa
24、ge.7.3 A typical system for laboratory use that can be as-sembled from readily available parts is shown schematically inFig. 1. The parts required are described in the followingsubsections.7.3.1 FlowmetersSeveral, sufficient to cover the rangefrom 0 to 15 L/min, calibrated by Practice D 3195.7.3.2 C
25、opper TubingApproximately 1 m long 3 ft by6.25 mm 0.25 in. in outside diameter for use as a heatexchanger in the water bath.7.3.3 Ball Joints (Ungreased) and Tubing, for the necessaryconnections. Butt seals may also be used made with inertmaterials such as polyethylene.7.3.4 Mixing Bulbto ensure ade
26、quate mixing of the per-meated gas and the diluent gas stream. A Kjeldahl trap isrecommended.7.3.5 Long Condenser, with large bore in which a thermom-eter and a permeation tube can be inserted.7.3.6 Temperature Controlled Water BathAbout 8-L2-gal capacity, capable of 60.1C or better water temperatur
27、econtrol, with a variable temperature control range from aboutNOTE 1This system has the advantage of smaller uncertainty of the temperature of the permeation tube.FIG. 1 Optional System for Laboratory Use of a Permeation TubeD 3609 00 (2005)215 to 35C, preferably equipped with a positive displacemen
28、ttype recirculating pump with at least 1-L/min liquid flow rateto supply water to the condenser.7.3.7 Thermometer, ASTM No. 91C or equivalent, cali-brated to 60.1C.7.3.8 Mercury Barometer.7.4 An alternate system is shown in Fig. 2. It has theadvantage of lower uncertainty of the temperature of thepe
29、rmeation tube. The required parts are described in the figure.8. Reagents and Materials8.1 Carrier Gas or Diluent Gas for Flow Over PermeationTubeCylinder of dry nitrogen or pure, dry air, or purifiedroom air (charcoal and drying agentinert air mover).8.1.1 Drier, indicating type and should be disca
30、rded whencolor changes.8.2 Diluent Gas for Blending with Carrier Stream Down-stream from Permeation Tube, free from impurities that wouldconsume test substances.9. Calibration of Permeation Tubes9.1 Permeation tubes may be calibrated gravimetrically bymeasurement of the weight loss occurring during
31、storage at aconstant temperature (4,5).Aslow stream of dry air or nitrogenshall flow over the tube during the calibration period. Aspecially constructed constant temperature chamber may beused or, if more convenient, the weight loss occurring duringuse of the tube in the actual flow system (7.2 and
32、7.3) can bemeasured. In the latter case, place the tube in its chamber(condenser) and run the system as described in Section 10.Remove the tube at 24-h intervals and weigh on a semimicroanalytical balance. Handle the tube with gloves or forceps tominimize pickup of moisture or grease. Remove the tub
33、e foronly the minimum time required for the weighing. Further-more, it is advisable to conduct the weighings when the relativehumidity does not exceed 50 %. Record the weighings to thenearest 0.01 mg. Because NO2permeation tubes may pick upmoisture on exposure to air, they may need to be weighed ona
34、 rigid time schedule to reproduce any mass changes as a resultof this cause (5). Repeat the weighing operation at scheduledintervals and plot the gross weight against elapsed time inminutes. The slope expressed as micrograms per minuterepresents the output of the tube. The total time usually neededt
35、o calibrate at a given temperature should not be less than fivedays. Alternatively, linear regression analysis may be used todetermine the permeation rate. Record measurements of per-meation rates at several temperatures and plot the results onsemilog paper to obtain the output at any temperature wi
36、thinthe calibration range. As a precaution against defective seals,check the first calibration after approximately two weeks; itshould be within 2 % of the initial value. If 2 % cannot beachieved, reject the tube.NOTE 1While permeation tube life may be extended by refrigeratedstorage, it is suggeste
37、d to store tubes at operating (or room) temperatureto avoid excessive preconditioning time.9.2 The frequency of recalibration will depend upon type ofpermeation tube, the quality of its construction and the careexercised in its use.9.2.1 Experience at the National Institute of Standards andTechnolog
38、y, with standard reference material permeation tubeshas indicated the following:9.2.1.1 SO2Permeation TubesCalibration is valid for oneyear or until 90 % of the liquid has permeated, whichevercomes first;9.2.1.2 NO2Permeation TubeCalibration is valid for sixmonths or until 90 % of the originally con
39、tained liquid haspermeated, whichever comes first.NOTE 1This system is constructed from readily available laboratory equipment.NOTE 2Warning: If the room temperature is significantly different from that of the water bath, a small difference in temperature between the bathand the condensor containing
40、 the permeation tube can exist. In this event, the temperature indicated by the thermometer in the condensor should be usedas that of the permeation tube, rather than that of the water bath.FIG. 2 Typical System for Laboratory UseD 3609 00 (2005)39.2.2 There has been insufficient experience in the u
41、se ofother kinds of permeation tubes as calibration standards topermit general statements. For such tubes, it is recommendedthat they be recalibrated immediately before use and at periodicintervals during use to establish any trends that may occur.10. Procedure10.1 Set up the flow system as describe
42、d in Section 7 andequilibrate at constant temperature.10.2 The concentration produced will depend upon the flowrate of the gas and the permeation rate. The latter depends inturn on the temperature of the permeation tube. Establish gasflow rates to produce concentrations desired, as calculated bythe
43、expression shown in 11.1. F1is conveniently maintained at0.05 to 0.1 L/min. F2may be any convenient value typicallyfrom 0.2 to 15 L/min.10.3 For commercially available equipment, follow themanufacturers instructions, which must be consistent with andmeet all the requirements of 10.1 and 10.2.10.4 Us
44、e output of the flow system to calibrate instruments,analyzers, or methods in the conventional manner.11. Calculation11.1 Primary Calculations:11.1.1 Determine the concentration of the gas mixture inparts per million by volume as follows:Cppmv!5 R/MW! 3 MV/F! (1)where:Cppm(v)= concentration in ppm b
45、y volume at 25C and101.3 kPa,R = permeation rate (gravimetric) g/min, corre-sponding to temperature of permeation tube,MV = molar volume (24.47 L at 25C and 101.3 kPa),F = F1+ F2= total flow rate of gas, L/min,F1= flow rate of carrier gas passing over permeationtube, L/min,F2= flow rate of diluent g
46、as, L/min, andMW = molecular weight of the permeand.NOTE 2All calculations made at operating temperatures and pres-sures.11.1.2 Concentrations may be reported in terms of mass andvolume, Cm, expressed in g/m3as follows:Cm5 Cppmv!3 MW 3 1000/24.47!3 P/101.3! 3 298.15/t 1 273.15!# (2)P = atmospheric p
47、ressure, kPa (mm Hg) andt = ambient temperature, C.11.2 Secondary Calculations:11.2.1 For convenience, standard conditions are establishedat 101.3 kPa (760 mm Hg) and 25C. This conforms with mostof the ASTM methods for atmospheric sampling and analysisthat involve volumetric corrections. Correction
48、of all volumesto these conditions is done as follows:Vs5 V 3 P/101.3! 3 298.15/t 1 273.15!# (3)where:Vs= gas volume, L at STP,V = measured volume in, L,P = barometric pressure, kPa (mm Hg), andt = measured temperature, C.NOTE 3If pressure measured is in mm Hg, the equation is the sameexcept 101.3 is
49、 replaced by 760 and the value for P in mm Hg is inserted.11.2.2 Dilution air flows may be corrected to standardconditions as follows:Fs5 F 3 P/101.3! 3 298.15/t 1 273.15!# (4)where:Fs= flow rate at standard conditions, L/min,F = measured rate of gas flow over the permeation tube,L/min,t = measured temperature, C, andP = barometric pressure, kPa (mm Hg).12. Precision and Bias12.1 The sources of error in the use of permeation devicesfor calibration purposes are evident from an inspection of therelationships given in Section 10.12.1.1 A
