1、Designation: E 1479 99 (Reapproved 2005)Standard Practice forDescribing and Specifying Inductively-Coupled PlasmaAtomic Emission Spectrometers1This standard is issued under the fixed designation E 1479; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, the year of last 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 the components of aninductively-coupled plasma atomic emissio
3、n spectrometer(ICP-AES) that are basic to its operation and to the quality ofits performance. This practice identifies critical factors affect-ing accuracy, precision, and sensitivity. It is not the intent ofthis practice to specify component tolerances or performancecriteria, since these are unique
4、 for each instrument. A prospec-tive user should consult with the vendor before placing anorder, to design a testing protocol to demonstrate that theinstrument meets all anticipated needs.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for inf
5、ormationonly.1.3 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. S
6、pecific safetyhazard statements are given in Section 13.2. Referenced Documents2.1 ASTM Standards:2E 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 158 Practice for Fundamental Calculations to ConvertIntensities into Concentrations in Optical Emission Spec-t
7、rochemical AnalysisE 172 Practice for Describing and Specifying the ExcitationSource in Emission Spectrochemical AnalysisE 416 Practice for Planning and Safe Operation of a Spec-trochemical LaboratoryE 520 Practice for Describing Photomultiplier Detectors inEmission and Absorption Spectroscopy3. Ter
8、minology3.1 DefinitionsFor terminology relating to emission spec-trometry, refer to Terminology E 135.4. Summary of Practice4.1 An ICP-AES is an instrument used to determine elemen-tal composition. It typically is comprised of several assembliesincluding a radio-frequency (RF) generator, an impedanc
9、ematching network (where required), an induction coil, a plasmatorch, a plasma ignitor system, a sample introduction system, alight gathering optic, an entrance slit and dispersing element tosample and isolate wavelengths of light emitted from theplasma, one or more devices for converting the emitte
10、d lightinto an electrical current or voltage, one or more analogpreamplifiers, one or more analog-to-digital converter(s), and adedicated computer with printer (see Fig. 13).4.1.1 The sample is introduced into a high-temperature(6000 K) plasma that is formed from the ionization of the gasstream cont
11、ained in the torch. The torch is inserted throughmetal tubing formed into a helix, which is called the load coil.Energy is applied to the load coil by means of an RF generator.4.1.2 The term inductively-coupled refers to the fact that thephysical phenomenon of induction creates a plasma by trans-fer
12、ring energy from the load coil to the gas stream that has beenmomentarily preionized by a high voltage ignitor electrode thatfunctions only during plasma ignition.4.2 When material passes through the plasma, it is vapor-ized, atomized, and many elements are almost completelyionized. Free atoms and i
13、ons are excited by collision from theirground states. When the excited atoms or ions subsequentlydecay to a lower energy state, they emit photons, some ofwhich pass through the entrance slit of a spectrometer. Eachelement emits a unique set of emission lines. Photons of adesired wavelength may be se
14、lected from the ultraviolet andvisible spectra by means of a dispersing element.4.2.1 Instruments may determine elements either simulta-neously or sequentially. The output of the detector generally isdirected to a preamplifier, an analog-to-digital converter, and acomputer which measures and stores
15、a value proportional tothe electrical current or voltage generated by the detector(s).1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry of Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current e
16、dition approved May 1, 2005. Published June 2005. Originallyapproved in 1992. Last previous edition approved in 1999 as E 1479 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume informat
17、ion, refer to the standards Document Summary page onthe ASTM website.3Courtesy of PerkinElmer, Inc., 761 Main Ave., Norwalk, CT 06859.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Using blank and known calibration solutions, a cali
18、brationcurve is generated for each element of interest.4.2.2 The computer compares the signals arising from thevarious elements in the sample to the appropriate calibrationcurve. The concentrations of more than 70 elements may bedetermined.4.3 Sensitivities (see 12.3) in a simple aqueous solution ar
19、eless than one part per million (ppm) for all of these elements,generally less than 10 parts per billion (ppb) for most, and mayeven be below 1 ppb for some.4.3.1 Organic liquids may also be used as solvents yieldingsensitivities that are within an order of magnitude of aqueouslimits for many common
20、 organic solvents. Some organicsolvents may afford detection limits similar or even superior tothose obtained using aqueous solutions.4.3.2 Direct sampling of solid materials has been performedsuccessfully by such techniques as spark or laser ablation andslurry nebulization. However, these require g
21、reater care in thechoice of reference materials and the operation of the samplingdevices. Solid materials, therefore, are usually dissolved priorto analysis.5. Significance and Use5.1 This practice describes the essential components of aninductively-coupled plasma atomic emission spectrometer(ICP-AE
22、S). The components include excitation/radio-frequency generators, sample introduction systems, spectrom-eters, detectors, and signal processing and displays. Thisdescription allows the user or potential user to gain a cursoryunderstanding of an ICP-AES system. This practice alsoprovides a means for
23、comparing and evaluating various sys-tems, as well as understanding the capabilities and limitationsof each instrument.5.2 TrainingThe vendor should provide training in safety,basic theory of ICP spectrochemical analysis, operations ofhardware and software, and routine maintenance for at leastone op
24、erator. Training ideally should consist of the basicoperation of the instrument at the time of installation, followedby an in-depth course one or two months later. Advancedcourses are also offered at several of the important spectros-copy meetings that occur throughout the year as well as byindepend
25、ent training institutes. Furthermore, several indepen-dent consultants are available who can provide training, inmost cases at the users site.6. Excitation/Radio Frequency Generators6.1 ExcitationA specimen is converted into an aerosolentrained in a stream of argon gas and transported through ahigh
26、temperature plasma. The plasma produces excited neutralatoms and excited ions. The photons emitted when excitedatoms or ions return to their ground states or lower energylevels are measured and compared to emissions from referencematerials of similar composition. For further details see Prac-tice E
27、172.6.2 Radio-Frequency Generator:6.2.1 An RF generator is used to initiate and sustain theargon plasma. Commercial generators operate at 27.12 and40.68 MHz since these frequencies are designated as clearfrequencies by U.S. Federal Communications Committee(FCC) regulations. Generators typically are
28、capable of produc-ing 1.0 to 2.0 kW for the 27.12 MHz generator and 1.0 to 2.3kW for the 40.68 MHz system.6.2.2 Generators more powerful than 2.5 kW are of limitedpractical analytical utility and are not commercially marketedwith ICP spectrometers. The power requirements are related totorch geometry
29、 and types of samples to be analyzed. Refer toFIG. 1 Components of Inductively Coupled Plasma3E 1479 99 (2005)2Practice E 172 for details. More power (typically 1.5 to 2 kWfor a 27.12 MHz system utilizing a 20-mm outside diametertorch and 1.2 to 1.7 kW for a 40.68 MHz generator) is requiredfor analy
30、zing samples dissolved in organic solvents than isneeded for aqueous solutions (approximately 1.0 kW). Lesspower is required for small diameter torches (for example, 650to 750 W for a 13-mm outside diameter torch).6.3 Load Coil:6.3.1 A coil made from copper (or another metal or an alloywith similar
31、electrical properties) is used to transmit powerfrom the generator to the plasma torch (see 7.6). A typicaldesign consists of a two- to six-turn coil of about 1-in. (25-mm)diameter, made from18-in. (3-mm) outside diameter and116-in. (1.6-mm) inside diameter copper tubing (though largertubing is used
32、 with two-turn coils). The tubing is fitted withferrules or similar devices to provide a leak-free connection toa coolant, either recirculated by a pump or fed from amunicipal water supply. Argon gas blown through the coil hasbeen used to cool other load coils.6.3.2 The high power conducted by the c
33、oil can lead to rapidoxidation, surface metal vaporization, RF arc-over and evenmelting if the coil is not cooled continuously.6.3.3 A safety interlock must be included to turn off the RFgenerator in case of loss of coolant flow.6.4 Impedance Matching:6.4.1 To optimize power transfer from the genera
34、tor to theinduced plasma, the output impedance of the generator must bematched to the input impedance of the load coil. Someinstruments include an operator-adjustable capacitor for im-pedance matching.6.4.2 Alternately, RF frequency may be automatically tunedor varied in free-running fashion against
35、 a fixed capacitor-inductor network. Most modern instruments, however, incor-porate an automatic impedance matching network to simplifyignition, to reduce incidence of plasma extinction when intro-ducing sample solutions, and to optimize power transfer.7. Sample Introduction7.1 The sample introducti
36、on system of an ICP instrumentconsists of a nebulizer, a spray chamber, and a torch.7.2 Nebulizers:7.2.1 Samples generally are presented to the instrument asaqueous or organic solutions. A nebulizer is employed toconvert the solution to an aerosol suitable for transport into theplasma where vaporiza
37、tion, atomization, excitation, and emis-sion occur.7.2.2 Some nebulizers, designated as self-aspirating pneu-matic nebulizers, operating on the Venturi principle, create apartial vacuum to force liquid up a capillary tube into thenebulizer. Precision of operation may be improved if a peri-staltic pu
38、mp controls the solution flow rate.7.2.3 Other nebulizers require an auxiliary device, such as aperistaltic pump, to drive solution to the nebulizer. Generally,pump-fed nebulizers are more tolerant of high levels ofdissolved solids and much less affected by suspended solidsand viscosity variations.7
39、.2.4 If fluoride is present in solutions to be analyzed, it isnecessary to employ a nebulizer fabricated from hydrofluoricacid (HF)-resistant materials (see 7.4.1.). It is possible to usethe HF-resistant nebulizer for most other types of solutions, butsensitivity and precision may be degraded. An HF
40、-resistantnebulizer may be more expensive to acquire and repair, andrequire greater operator proficiency and training than othernebulizers.7.3 Self-Aspirating or Non-Pump-Fed Nebulizers:7.3.1 Concentric Glass Nebulizers (CGN):7.3.1.1 CGNs consist of a fine capillary through which thesample solution
41、flows surrounded by a larger tube drawn to afine orifice (concentric) slightly beyond the end of the centralcapillary (see Fig. 2). Minor variations in capillary diameterand placement affect optimal operating pressure for the samplegas flow and change the sample solution uptake rate. Uptakerates of
42、liquid are typically 0.5 to 3 mL/min.7.3.1.2 CGNs exhibit somewhat degraded sensitivity andprecision for solutions that approach saturation or concentra-tions of more that a few tenths of a percent of dissolved solids.This problem can be greatly reduced by using an inner argonstream that has been bu
43、bbled through water in order tohumidify the sample gas argon. Furthermore, since suspendedsolids may clog the tip, it is desirable to include a piece ofcapillary tubing of even smaller diameter in the samplesolution uptake line. This action will isolate a potentialclogging problem prior to clogging
44、at the nebulizer tip.7.3.2 Micro-Concentric Nebulizer (MCN):7.3.2.1 To some extent, the MCN mimics the concept andfunction of the CGN but the MCN employs a thinner-walledpoly-ether-imide capillary and TFE-fluorocarbon (or otherpolymer) outer body to minimize or eliminate undesirable largedrop format
45、ion and facilitate HF tolerance (see Fig. 33,4). Atrue aerosol, as opposed to a mist, is produced consisting ofonly the desired smallest size droplets. Liquid uptake rates toproduce similar sensitivity to CGNs are sharply reduced withthe MCN. The MCN utilizes typical uptake rates of 0.1mL/min and is
46、 HF tolerant. Unusually small sample size, lowuptake rates, fast washout times, and very low drain ratescharacterize this nebulizer. The low uptake rate is particularlybeneficial for extending limited sample volumes so that the4Courtesy of CETAC Technologies, a division of Transgenomic Inc., 5600 S.
47、42nd St., Omaha, NE.FIG. 2 Concentric Glass Nebulizer (CGN)3E 1479 99 (2005)3long nebulization times encountered with sequential spectrom-eters undertaking multielement analysis may be successfullyaccomplished.7.3.2.2 The initial purchase cost is higher for the MCN thanfor the CGN but the cost may b
48、e offset by a substantialreduction in recurring hazardous waste disposal cost (forexample, heavy metal salts, mineral acids, etc.). This disposalcost reduction is because of the minimal waste volume inherentwith low sample uptake rates and significantly reduced drainrates. In addition, micro-autosam
49、plers that are compatible withthe MCN are available for the optimum handling of smallsample volumes.7.3.3 Cross-Flow Nebulizer (CFN)Consists of two capil-laries held perpendicularly and with exit tips close together, asshown in Fig. 4. This nebulizer is preadjusted by the manu-facturer and is known as a fixed cross-flow nebulizer. Itrequires little maintenance and is very durable. Problems withhigh levels of dissolved and suspended solids are similar tothose of the concentric glass nebulizer.7.4 Pump-Fed Pneumatic Nebulizers:7.4.1 Grid Nebulizerconstructed from a fine-mesh
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