1、Designation: E1184 10 (Reapproved 2016)Standard 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 o
2、f revision, 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 practice covers a procedure for the determinationof microgram per millilitre (g/mL) or lo
3、wer concentrations 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 w
4、hich should result 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
5、 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. Specific safetyhazard statements are given in Se
6、ction 9.2. Referenced 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 Re
7、lated MaterialsE406 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 atomizationt
8、he formation of ground 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 origin
9、al matrix,but not 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 temperatu
10、re is increasedduring 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, forexa
11、mple, methane, at 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 ste
12、ps. It is usually 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
13、for mostinstruments 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.5. Theory of Atomic Ab
14、sorption Spectrometry (AAS)5.1 In flame atomic absorption spectrometry (Flame-AAS),a test solution is aspirated into a flame through which passes1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibil
15、ity ofSubcommittee E01.20 on Fundamental Practices.Current edition approved April 1, 2016. Published May 2016. Originallyapproved in 1987. Last previous edition approved in 2010 as E1184 10. DOI:10.1520/E1184-10R16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM
16、Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1radiation from a line emission s
17、ource of the element 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
18、concentration can 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, emitte
19、d by a specific element 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
20、the external light 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
21、 graphite furnace.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
22、proposed toexplain 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 e
23、t al. (4).7. Apparatus7.1 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 h
24、eated to high temperatures, 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
25、 usedelectrothermal 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 si
26、zedepending upon a 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 graphitetu
27、be is constructed 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
28、less than 1 s. Temperatures 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
29、and accessories such 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, the
30、y will not be covered 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
31、, or othersuitable 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 reco
32、rder tracing. This 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 abs
33、orption versus time 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-m
34、ined by means of graphite 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) electric
35、alservice. Electrical 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 Ha
36、zardThe inert or non-oxidizingatmosphere required in the graphite furnace during heatingcycles is usually maintained by using argon or nitrogen gasdelivered from portable gas cylinders.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.E1184 10 (2016)29.2.1
37、 Sufficient space shall be 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 col
38、or coding.9.2.2 Two-stage 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 val
39、ves,and tubing for gas transport when designing a gas deliverysystem.9.2.3 Reserve gas cylinders should not be stored in thelaboratory area. Gas storage areas shall be adequatelyventilated, fire-resistant, located away from sources of ignitionor excessive heat, and dry. All cylinders shall be chaine
40、d inplace or placed in partitioned cells to prevent them from fallingover. In all cases, storage areas shall comply with local, state,and municipal requirements as well as with the standards of theCompressed Gas Association and the National Fire PreventionAssociation. Access to gas storage areas sho
41、uld be limited toauthorized personnel.9.3 Chemical HazardPractice E50 should be consulted forrecommendations and precautions concerning chemical haz-ards.9.4 VentilationAsmall hood is required to carry away anytoxic fumes that may result from the atomization process.Follow the manufacturers instruct
42、ions for proper hood instal-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
43、 laboratory.9.6 Laboratory 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 t
44、he graphite tube,should be 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 ato
45、mic absorption unit is provided 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 thepresc
46、ribing or installing physician, 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
47、drying, pyrolysis, and atomi-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 rec
48、ommended parameters for aparticular 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 d
49、etermined experimentally (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
