1、Designation: E1184 10Standard Practice forDetermination of Elements by Graphite Furnace AtomicAbsorption Spectrometry1This standard is issued under the fixed designation E1184; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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 practice covers a procedure for the determinationof microgram per millilitre (g/mL) or lower concentrations
3、 ofelements in solution using a graphite furnace attached to anatomic absorption spectrometer. A general description of theequipment is provided. Recommendations are made for pre-paring the instrument for measurements, establishing optimumtemperature conditions and other criteria which should result
4、 indetermining a useful calibration concentration range, andmeasuring and calculating the test solution analyte concentra-tion.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of
5、 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. Specific safetyhazard statements are given in Section 9.2. Referen
6、ced Documents2.1 ASTM Standards:2E50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE131 Terminology Relating to Molecular SpectroscopyE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE40
7、6 Practice for Using Controlled Atmospheres in Spec-trochemical AnalysisD1193 Specification for Reagent Water3. Terminology3.1 Refer to Terminologies E131 and E135 for the definitionof terms used in this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 atomizationthe formation of gr
8、ound state atoms thatabsorb radiation from a line emission source. The atomizationprocess in graphite furnace atomic absorption spectrometry(GF-AAS) analysis is covered in 6.2.3.2.2 pyrolysisthe process of heating a specimen to atemperature high enough to remove or alter its original matrix,but not
9、so high as to volatilize the element to be measured. Thepurpose of the pyrolysis step in GF-AAS analysis is to removeor alter the original specimen matrix, thereby reducing oreliminating possible interferences to the formation of groundstate atoms that are formed when the temperature is increaseddur
10、ing the atomization step. Many publications and referenceswill refer to pyrolysis as charring or ashing.3.2.3 pyrolytic graphite coatinga layer of pyrolytic graph-ite that coats a graphite tube used in GF-AAS analysis.Pyrolytic graphite is formed by pyrolizing a hydrocarbon, forexample, methane, at
11、2000 C.3.2.4 rampinga slow, controlled increase of the tempera-ture in the graphite tube. Ramping will provide for an efficientbut not too rapid removal or decomposition of the specimenmatrix. Most graphite furnaces allow for ramping during thedrying, pyrolysis, and atomization steps. It is usually
12、employedduring the drying and pyrolysis steps. However, some instru-ment manufacturers may recommend ramping during theatomization step depending on the specimen matrix and theelement being measured (for example, the analysis of cadmiumor lead in hair or blood). The power supplies for mostinstrument
13、s also allow the rate of the temperature increase tobe varied.4. Significance and Use4.1 This practice is intended for users who are attempting toestablish GF-AAS procedures. It should be helpful for estab-lishing a complete atomic absorption analysis program.1This practice is under the jurisdiction
14、 of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current edition approved June 1, 2010. Published August 2010. Originallyapproved in 1987. Last previous edition approved in 2002 as E1
15、184 02. DOI:10.1520/E1184-10.2For 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 Summary page onthe ASTM website.1Copyright ASTM International, 1
16、00 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Theory of Atomic Absorption Spectrometry (AAS)5.1 In flame atomic absorption spectrometry (Flame-AAS),a test solution is aspirated into a flame through which passesradiation from a line emission source of the eleme
17、nt sought.The radiation of the element sought is absorbed in proportionto the concentration of its neutral atoms present in the flame.The concentration of the analyte is obtained by comparison tocalibrations.5.2 The theoretical basis for using atomic absorption todetermine analyte concentration can
18、be found in texts oninstrumental analysis in analytical chemistry and in the litera-ture.6. Theory of Graphite Furnace Atomic AbsorptionSpectrometry6.1 Basic TechniqueA discrete amount of test solution isheated in a graphite furnace to produce a cloud of neutralatoms. Light, emitted by a specific el
19、ement from a line sourceat a specific wavelength, is passed through the cloud andneutral atoms of this same element in the cloud absorb some ofthis light. Thus, the intensity of the beam is decreased at thewavelengths characteristic of the element. This absorbance ofradiation from the external light
20、 source depends on thepopulation of the neutral atoms and is proportional to theconcentration of the element in the test solution.6.2 Graphite Furnace Atomization Thermodynamic andkinetic theories must be considered to fully understand theatomization process that takes place in the graphite furnace.
21、Jackson (1)3and also Campbell and Ottaway (2) provide acomplete discussion of the thermodynamic theory. They alsodiscuss thermal dissociation of metal oxides, reduction ofmetal oxides, evaporation of metal oxides prior to atomization,and carbide formation. Several models have been proposed toexplain
22、 the theory of kinetic atomization. A search of theliterature will find discussions of atomization under increasingtemperature, and atomization under isothermal conditions (3).Additional discussion and clarification of the kinetic atomiza-tion theory is provided by Paveri-Fontana et al. (4).7. Appar
23、atus7.1 Atomic Absorption SpectrometerMost flame atomicabsorption spectrometers manufactured currently can be easilyadapted for graphite furnace analysis.7.1.1 Automatic background correction is necessary for allspectrometers used with graphite furnaces. When graphitefurnaces are heated to high temp
24、eratures, background fromabsorption is produced within the graphite tube. Also, smallamounts of particulate matter in the furnace contribute to thebackground signal. Therefore, it is essential to correct orcompensate for this background.7.2 Electrothermal AtomizersThe most commonly usedelectrotherma
25、l atomizer is the graphite tube furnace. Thisatomizer consists of a graphite tube positioned in a water-cooled unit designed to be placed in the optical path of thespectrometer so that the light from the hollow cathode lamppasses through the center of the tube. The tubes vary in sizedepending upon a
26、 particular instrument manufacturers furnacedesign. These tubes are available with or without pyrolyticgraphite coating. However, because of increased tube life,tubes coated with pyrolytic graphite are commonly used. Thewater- cooled unit or atomizer head which holds the graphitetube is constructed
27、in such a way that an inert gas, usuallyargon or nitrogen, is passed over, around, or through thegraphite tube to protect it from atmospheric oxidation. Theheating of all of these atomizers is controlled by powersupplies which make it possible to heat the graphite tube to3000 C in less than 1 s. Tem
28、peratures and drying, pyrolysis,and atomization times are controlled by these power supplies(determination of these parameters is covered later in Section10). The flow of the inert gas through the atomizer head also iscontrolled by the power supplies.7.2.1 Other types of atomizers and accessories su
29、ch as thegraphite cup, graphite rod, Lvov platform, tantalum filament,and tantalum boat have been used and are covered in theliterature. With the exception of the Lvov platform, they havenot enjoyed the widespread and general use that the graphitetube atomizers have. Therefore, they will not be cove
30、red indetail within this practice. A good general description of theseother units can be found in the literature.7.3 Signal Output SystemThe output signal resulting fromthe atomization of a specimen may be displayed by a strip chartrecorder, video display, digital computer, printer, or othersuitable
31、 device depending on the electronic capability of thespectrometer employed.7.3.1 If a strip chart recorder is used, it must have a fullscale response of 0.5 s or less. Normally, when a strip chartrecorder is used, the absorption is determined by measuring thepeak height of the recorder tracing. This
32、 procedure is appro-priate because the absorption signal generated by a graphitefurnace atomizer usually results in a very narrow peak (absorp-tion versus time). However, some specimen matrices mayrequire instrumental parameters (for example, ramping), whichwill result in broad absorption versus tim
33、e peaks. In such cases,peak area measurement may be more appropriate. The instru-ment manufacturers manual should be consulted to determinewhich procedure is most suitable for the instrument being used.8. Reagents and Materials8.1 Picogram quantities of some elements can be deter-mined by means of g
34、raphite furnace atomization. Therefore,ultra-pure acids and Type I (Specification D1193) water shallbe used to prepare calibration solutions and test solutions.9. Hazards9.1 Electrical HazardsThe power supplies for graphitefurnaces require high-voltage (greater than 200 V) electricalservice. Electri
35、cal power shall be supplied as determined fromload requirements in accordance with the latest revision of theNational Electrical Code. The recommendations of the equip-ment manufacturers and local engineers should be followed indesigning the electrical service.9.2 Compressed Gas HazardThe inert or n
36、on-oxidizingatmosphere required in the graphite furnace during heating3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.E1184 102cycles is usually maintained by using argon or nitrogen gasdelivered from portable gas cylinders.9.2.1 Sufficient space shall b
37、e provided for the cylinders,which shall be kept in a vertical position and always wellsecured. They shall not be used or stored near burners, hotplates, or in any area where the temperature exceeds 52 C(125 F). The contents shall be identified with labels or stencilsand color coding.9.2.2 Two-stage
38、 regulators with pressure gages should beused as part of the basic flow system to deliver requiredcylinder gas to the instrument at a reduced pressure. PracticeE406 and the manufacturers instructions should be followedwith regard to the types of regulators, flow-metering valves,and tubing for gas tr
39、ansport when designing a gas deliverysystem.9.2.3 Reserve gas cylinders should not be stored in thelaboratory area. Gas storage areas shall be adequately venti-lated, fire-resistant, located away from sources of ignition orexcessive heat, and dry. All cylinders shall be chained in placeor placed in
40、partitioned cells to prevent them from falling over.In all cases, storage areas shall comply with local, state, andmunicipal requirements as well as with the standards of theCompressed Gas Association and the National Fire PreventionAssociation. Access to gas storage areas should be limited toauthor
41、ized personnel.9.3 Chemical HazardPractice E50 should be consultedfor recommendations and precautions concerning chemicalhazards.9.4 VentilationAsmall hood is required to carry away anytoxic fumes that may result from the atomization process.Follow the manufacturers instructions for proper hood inst
42、al-lation.9.5 LaboratoryThe laboratory in which the graphite fur-nace is operated shall be kept as clean as possible. Anyprocedures that may produce an atmosphere that is corrosive tothe instrumentation or detrimental to the analysis of thespecimen should be removed from the laboratory.9.6 Laborator
43、y ApparatusIt is imperative that all labora-tory apparatus and containers used in the preparation ofcalibration and test solutions be acid cleaned. All laboratoryware, including plastic tips used on micropipets for the transferof calibration solutions and test solutions to the graphite tube,should b
44、e acid rinsed before being used. Once laboratory wareis acid rinsed, all of the items that come in contact withanalytical solutions shall be isolated from subsequent contactwith fingers, clothing, bench tops, etc.9.7 Magnetic Background CorrectionIf the graphite fur-nace atomic absorption unit is pr
45、ovided with a backgroundcorrection that does or can produce a magnetic field, the unitshould not be operated by an individual who wears, internallyor externally, a medical device such as a pacemaker, that can beaffected by the magnetic field, without the approval of theprescribing or installing phys
46、ician, or both. In addition anappropriate warning sign should warn visitors of the magneticfield.10. Preparation of Apparatus10.1 Graphite Furnace ParametersAll graphite furnacesare resistance-heated by power supplies that provide individu-ally controlled heating stages for drying, pyrolysis, and at
47、omi-zation. The means to control the times and temperatures ofthese stages will vary with instrumentation. Most manufactur-ers provide a listing of the parameters required for the graphitefurnace analysis of numerous elements in the most commonlyencountered matrices. The recommended parameters for a
48、particular element should be verified for the specific instrumentbeing used with an appropriate solution. Also, for samplematrices that differ from those printed in the manufacturerslist, the most appropriate time and temperature setting for eachstage must be calculated or determined experimentally
49、(see10.1.1).NOTE 1Ramping is normally used during the drying and pyrolysisstages. Some procedures may also recommend that ramping be usedduring the atomization stage, depending upon the specimen matrix and theelement being measured. Refer to the instrument manufacturers manualof the particular instrument for the recommended ramp rates, if any, forthe type of solution being analyzed.10.1.1 DryingThe drying stage is a low temperature stagein which the graphite tube is heated to a temperature highenough to evaporate, but not boil, any solvent. The ideal
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1