1、Designation: E1832 08 (Reapproved 2012)Standard Practice forDescribing and Specifying a Direct Current Plasma AtomicEmission Spectrometer1This standard is issued under the fixed designation E1832; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of 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 describes the components of a directcurrent plasma (DCP) atomic emission spect
3、rometer. Thispractice does not attempt to specify component tolerances orperformance criteria. This practice does, however, attempt toidentify critical factors affecting bias, precision, and sensitivity.A prospective user should consult with the vendor beforeplacing an order to design a testing prot
4、ocol for demonstratingthat the instrument meets all anticipated needs.1.2 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
5、 applica-bility of regulatory limitations prior to use. Specific hazardsstatements are give in Section 9.2. Referenced Documents2.1 ASTM Standards:2E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE158 Practice for Fundamental Calculations to ConvertIntensities
6、 into Concentrations in Optical Emission Spec-trochemical Analysis (Withdrawn 2004)3E172 Practice for Describing and Specifying the ExcitationSource in Emission SpectrochemicalAnalysis (Withdrawn2001)3E406 Practice for Using Controlled Atmospheres in Spec-trochemical AnalysisE416 Practice for Planni
7、ng and Safe Operation of a Spec-trochemical Laboratory (Withdrawn 2005)3E520 Practice for Describing Photomultiplier Detectors inEmission and Absorption SpectrometryE528 Practice for Grounding Basic Optical Emission Spec-trochemical Equipment (Withdrawn 1998)3E1097 Guide for Determination of Various
8、 Elements byDirect Current Plasma Atomic Emission Spectrometry3. Terminology3.1 For terminology relating to emission spectrometry, referto Terminology E135.4. Significance and Use4.1 This practice describes the essential components of theDCP spectrometer. This description allows the user or potentia
9、luser to gain a basic understanding of this system. It alsoprovides a means of comparing and evaluating this system withsimilar systems, as well as understanding the capabilities andlimitations of each instrument.5. Overview5.1 A DCP spectrometer is an instrument for determiningconcentration of elem
10、ents in solution. It typically is comprisedof several assemblies including a direct current (dc) electricalsource, a sample introduction system, components to form andcontain the plasma, an entrance slit, elements to disperseradiation emitted from the plasma, one or more exit slits, oneor more photo
11、multipliers for converting the emitted radiationinto electrical current, one or more electrical capacitors forstoring this current as electrical charge, electrical circuitry formeasuring the voltage on each storage device, and a dedicatedcomputer with printer. The liquid sample is introduced into as
12、pray chamber at a right angle to a stream of argon gas. Thesample is broken up into a fine aerosol by this argon stream andcarried into the plasma produced by a dc-arc discharge betweena tungsten electrode and two or more graphite electrodes.When the sample passes through the plasma, it is vaporized
13、and atomized, and many elements are ionized. Free atoms andions are excited from their ground states. When electrons ofexcited atoms and ions fall to a lower-energy state, photons ofspecific wavelengths unique to each emitting species areemitted. This radiation, focussed by a lens onto the entrance
14、slitof the spectrometer and directed to an echelle grating and1This practice is under the jurisdiction 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 Dec. 1,
15、 2012. Published December 2012. Originallyapproved in 1996. Last previous edition approved in 2003 as E1832 03, which waswithdrawn October 2004 and reinstated in May 2008. DOI: 10.1520/E1832-08R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service a
16、t serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohoc
17、ken, PA 19428-2959. United States1quartz prism, is dispersed into higher orders of diffraction.Control on the diffraction order is accomplished by thelow-dispersion echelle grating. Radiation of specific wave-length or wavelengths passes through exit slits and impinges ona photomultiplier or photomu
18、ltipliers. The current outputscharge high-quality capacitors, and the voltages thus generatedare measured and directed to the computer. Using calibrationsolutions, a calibration curve is generated for each element ofinterest. The computer compares the signals arising from themany elements in the sam
19、ple to the appropriate calibrationcurve and then calculates the concentration of each element.Over seventy elements may be determined. Detection limits ina simple aqueous solution are less than 1 mg/L for most ofthese elements. Mineral acids or organic liquids also may beused as solvents, and detect
20、ion limits are usually within anorder of magnitude of those obtained with water. Detectionlimits may be improved by using preconcentration procedures.Solid samples are dissolved before analysis.6. Description of Equipment6.1 Echelle SpectrometerComponents of the equipmentshown in Fig. 1 and describe
21、d in this section are typical of acommercially available spectrometer.Although a specific spec-trometer is described herein, other spectrometers having equalor better performance may be satisfactory. The spectrometer isa Czerny-Turner mount and consists of a condensing lens infront of an entrance sl
22、it, a collimating mirror, combineddispersing elements (grating and prism), focus mirror, exit slits,photomultipliers, control panel, and wavelength selectormechanism.6.1.1 Condensing Lens, placed between the DCP source andthe entrance slit. It should have a focal length capable offocusing an image o
23、f the source on the entrance slit and withsufficient diameter to fill the aperture of the spectrometer withradiant energy.6.1.2 Entrance Slit, although available with fixed width andheight, a slit variable in both width and height provides greaterflexibility. Typical values are 0.025 mm to 0.500 mm
24、in widthand 0.100 mm to 0.500 mm in height. Adjustable slit widthsand heights are useful in obtaining optimal spectral band widthand radiant energy entering the spectrometer for the require-ments of the analytical method.6.1.3 Collimating Mirror, renders all rays parallel afterentering the spectrome
25、ter. These parallel rays illuminate thecombined dispersing elements. The focal length and f numbershould be specified. Typical focal length and f number are 750mm and f/13.6.1.4 Combined Dispersing Components, positioned so thatthe radiant energy from the collimating mirror passes throughthe prism,
26、is refracted and reflected by a plane grating and backthrough the prism. Specify the ruling on the grating (forexample, 79 grooves/mm).6.1.5 Focus Mirror, placed to focus the radiant energy fromthe combined dispersing elements on a flat two-dimensionalfocal plane where the exit slits are located.6.1
27、.6 Fixed Exit Slits, mounted in a removable fixture calledan optical cassette for multielement capability. A two-mirrorperiscope behind each exit slit directs the radiant energy to acorresponding photomultiplier. For single element capability,energy for one wavelength usually passes through its exit
28、 slitdirectly to the photomultiplier without the need for a periscope.Select the specific exit slit width before installation. Provide asingle channel cassette with one exit slit variable from 0.025mm to 0.200 mm in width and from 0.100 mm to 0.500 mm inlength.6.1.7 Photomultipliers, up to twenty en
29、d-on tubes, aremounted behind the focal plane in a fixed pattern. Considersensitivity at specific wavelength and dark current in theselection of appropriate photomultipliers. Provide variablevoltage to each photomultiplier to change its response asrequired by the specific application. A typical rang
30、e is from550 V to 1000 V in 50-V steps. A survey of the properties ofphotomultipliers is given in Practice E520.6.1.8 Control Panels, are provided to perform several func-tions and serve as input to microprocessors to control theoperation of the spectrometer. Provide a numeric keyboard toenter high
31、and low concentrations of reference materials forcalibration and standardization of each channel and to displayentered values for verification. Provide a switch on this panelto set the mode either to integrate during analysis or to measureinstantaneous intensity. The latter mode is required to obtai
32、nthe peak position for a specific channel by seeking maximumintensity by wavelength adjustment and verifying by wave-length scanning. Conduct interference and background inves-tigations with this mode. Scanning is required if automaticbackground correction is to be performed. Provide othernecessary
33、switches for the following purposes: to calibrate orstandardize the spectrometer, start analysis, interrupt the func-tion being performed, set integration time and the number ofFIG. 1 Echelle Grating SpectrometerE1832 08 (2012)2replicate analyses, and direct the output to a printer, display, orstora
34、ge medium. Impose a fixed time delay of 10 s beforeintegration can begin to ensure that the solution being analyzedis aspirated into the DCP discharge. Provide digital and analogvoltmeters for displaying the instantaneous or integrated inten-sities during peaking, scanning, or analysis. If a compute
35、r is anintegral part of the spectrometer, most of the control functionsare accomplished with software.6.1.9 Wavelength Adjustment, provided to adjust the wave-length range and diffraction order for peaking the spectrometerbecause a two-dimensional spectrum is produced. Both coarseand final control o
36、f these adjustments are required. To maintainoptical alignment, the spectrometer should be thermally iso-lated from the DCP source or heated. A heated base on whichthe spectrometer rests has been satisfactory for this purpose.6.1.10 Dispersion and Spectral Band PassTypical disper-sion and spectral b
37、and pass with a 0.025-mm slit width varyfrom 0.061 nm/mm and 0.0015 nm at 200 nm to 0.244 nm/mmand 0.0060 nm at 800 nm, respectively.6.2 DCP Source, composed of several distinct parts, namelythe electrode, direct current power supply, gas flow, sampleintroduction, exhaust, water cooling, and safety
38、systems. Referto Practice E172 for a list of the electrical source parametersthat should be specified in a DCP method.6.2.1 Electrode System, Fig. 2, consists of two graphiteanodes fixed in a vertical plane and at a typical angle of 60 toone another, and a tungsten cathode fixed in a horizontal plan
39、eat an angle of 45 to the optic axis. In their operating position,the tips of the two anodes are separated by a distance of 1316in., (3.0 cm), and the tungsten cathode is 158 in., (4.1 cm),above the anode tips. Each electrode is recessed in a ceramicsleeve fitted into water-cooled anode and cathode
40、blocks.Because the electrodes are of special design to fit into and beheld by these blocks, the user must follow the manufacturersrecommendations for these electrodes. The electrode systemshall provide mechanism to adjust the electrodes vertically andhorizontally across the optic axis to properly pr
41、oject the imageof the excitation region onto the entrance slit and obtain amaximum signal-to-noise ratio. Sometimes a visible excitationregion is not produced when some specimens are aspirated intothis source. Iron solutions, as well as solutions of several otherelements, however, are satisfactory f
42、or this purpose.6.2.2 Direct Current Power Supply, capable of maintaininga constant current of 7 A dc in the discharge with a voltage of40 V to 50 V dc between the anodes and cathodes. Theresulting discharge has the shape of an inverted letter Y with aluminous zone in the crotch of the Y.6.2.3 Gas F
43、low System, (Refer to Practice E406) shall becapable of the following:6.2.3.1 Providing argon gas delivered at a pressure of 80 psi(5.62 kg/cm2) to the discharge sustaining gas and samplenebulization.6.2.3.2 Providing a pneumatic system to extend the anodeand cathode out of their sleeves and move th
44、e cathode blockdownwards so that the cathode electrode makes contact withone of the anodes and initiates the plasma.6.2.3.3 Providing gas pressures of 15 psi to 30 psi (1.05kg/cm2to 2.01 kg/cm2) for nebulization and 50 psi (3.52kg/cm2) for other functions. Needle valves are used to adjustthese press
45、ures, as well as provide for division of gas flowsamong three electrode blocks. A balance among the gas flowsthrough these blocks and past the electrodes is necessary toproduce and maintain a symmetrical discharge and atriangular- or arrowhead-shaped excitation region where thespecimens spectrum is
46、generated.6.2.3.4 Providing isolation of the gas flow system from theambient atmosphere. For good analytical performance, ensurethat all tubing connections are tight and O-rings are in goodcondition.6.2.4 Sample Introduction System is required to control theflow of sample solution. This typically in
47、volves placing aflexible tube in the sample container, which aspirates thesample solution into a nebulizer, usually a cross-flow design. Aperistaltic pump is used to pump the sample solution to thenebulizer.As a specimen drop is formed at the nebulizer orifice(0.02 in. or 0.05 cm), it is removed by
48、the argon stream andbroken into several smaller drops. Most of these impinge onthe walls of the spray chamber running down to collect in awaste reservoir. Typically, about 20 % of the nebulized speci-men is carried by the argon stream as an aerosol into theplasma. The liquid in the waste reservoir i
49、s removed continu-ously by the same peristaltic pump used to feed the nebulizer,and passes the waste through a second tube to be safelydisposed. If this is not done, the volume of liquid waste in thereservoir and the spray chamber is increased, increasing the gaspressure and volume of the specimen injected into the plasma,thus extinguishing the plasma. Because this pump crushesthese tubes with use, daily damage inspection is required foroptimum performance.6.2.5 Exhaust SystemProvide a small hood connected toan exhaust fan above the plasma cabinet to remove the wastegases.
