1、Designation: E1479 99 (Reapproved 2011)Standard Practice forDescribing and Specifying Inductively-Coupled PlasmaAtomic Emission Spectrometers1This standard is issued under the fixed designation E1479; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case 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 aninductively-coupled plasma atomic emission s
3、pectrometer(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 fo
4、r 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 asstandard. The values given in parentheses are for informatio
5、nonly.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. Specific
6、 safetyhazard statements are given in Section 13.2. Referenced Documents2.1 ASTM Standards:2E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE158 Practice for Fundamental Calculations to ConvertIntensities into Concentrations in Optical Emission Spec-trochemica
7、l Analysis3E172 Practice for Describing and Specifying the ExcitationSource in Emission Spectrochemical Analysis3E416 Practice for Planning and Safe Operation of a Spec-trochemical Laboratory3E520 Practice for Describing Photomultiplier Detectors inEmission and Absorption Spectrometry3. Terminology3
8、.1 DefinitionsFor terminology relating to emission spec-trometry, refer to Terminology E135.4. 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 impedancematching
9、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 emitted lightint
10、o an electrical current or voltage, one or more analogpreamplifiers, one or more analog-to-digital converter(s), and adedicated computer with printer (see Fig. 14).4.1.1 The sample is introduced into a high-temperature(6000 K) plasma that is formed from the ionization of the gasstream contained in t
11、he 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-ferring energ
12、y 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 ions are ex
13、cited 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 selected fro
14、m the ultraviolet andvisible spectra by means of a dispersing element.4.2.1 Instruments may determine elements either simultane-ously or sequentially. The output of the detector generally isdirected to a preamplifier, an analog-to-digital converter, and a1This practice is under the jurisdiction of A
15、STM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current edition approved Nov. 15, 2011. Published June 2012. Originallyapproved in 1992. Last previous edition approved in 2005 as E1479 99
16、 (2005).DOI: 10.1520/E1479-99R11.2For 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.3Withdrawn. The last approve
17、d version of this historical standard is referencedon www.astm.org.4Courtesy 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 Sputer which measures and stores a value proportional tothe
18、electrical current or voltage generated by the detector(s).Using blank and known calibration solutions, a calibrationcurve 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 concent
19、rations of more than 70 elements may bedetermined.4.3 Sensitivities (see 12.3) in a simple aqueous solution areless 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
20、 used as solvents yieldingsensitivities that are within an order of magnitude of aqueouslimits for many common 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 perfor
21、medsuccessfully by such techniques as spark or laser ablation andslurry nebulization. However, these require greater 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 p
22、ractice describes the essential components of aninductively-coupled plasma atomic emission spectrometer(ICP-AES). The components include excitation/radio-frequency generators, sample introduction systems, spectrom-eters, detectors, and signal processing and displays. Thisdescription allows the user
23、or potential user to gain a cursoryunderstanding of an ICP-AES system. This practice alsoprovides a means for 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 o
24、f ICP spectrochemical analysis, operations ofhardware and software, and routine maintenance for at leastone operator. 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 o
25、ffered at several of the important spectros-copy meetings that occur throughout the year as well as byindependent 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 Exci
26、tationA specimen is converted into an aerosolentrained in a stream of argon gas and transported through ahigh 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
27、and compared to emissions from referencematerials of similar composition. For further details see Prac-tice E172.6.2 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 design
28、ated as clearfrequencies by U.S. Federal Communications Committee(FCC) regulations. Generators typically are 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.FIG. 1 Components of Inductively Coupled Plasma1E1479 99 (2011)26.2.2 Generators more
29、 powerful than 2.5 kW are of limitedpractical analytical utility and are not commercially marketedwith ICP spectrometers. The power requirements are related totorch geometry and types of samples to be analyzed. Refer toPractice E172 for details. More power (typically 1.5 to 2 kWfor a 27.12 MHz syste
30、m utilizing a 20-mm outside diametertorch and 1.2 to 1.7 kW for a 40.68 MHz generator) is requiredfor analyzing 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 out
31、side diameter torch).6.3 Load Coil:6.3.1 A coil made from copper (or another metal or an alloywith similar 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
32、-in. (3-mm) outside diameter and116-in. (1.6-mm) inside diameter copper tubing (though largertubing is used 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. Arg
33、on gas blown through the coil hasbeen used to cool other load coils.6.3.2 The high power conducted by the coil 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 RFgenera
34、tor in case of loss of coolant flow.6.4 Impedance Matching:6.4.1 To optimize power transfer from the generator 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 m
35、atching.6.4.2 Alternately, RF frequency may be automatically tunedor varied in free-running fashion against 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 in
36、tro-ducing sample solutions, and to optimize power transfer.7. Sample Introduction7.1 The sample introduction 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 nebu
37、lizer is employed toconvert the solution to an aerosol suitable for transport into theplasma where vaporization, 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 forc
38、e liquid up a capillary tube into thenebulizer. Precision of operation may be improved if a peri-staltic pump 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 tole
39、rant of high levels ofdissolved solids and much less affected by suspended solidsand viscosity variations.7.2.4 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
40、-resistant nebulizer for most other types of solutions, butsensitivity and precision may be degraded. An HF-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 C
41、oncentric Glass Nebulizers (CGN):7.3.1.1 CGNs consist of a fine capillary through which thesample solution 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 op
42、timal operating pressure for the samplegas flow and change the sample solution uptake rate. Uptakerates of 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 per
43、cent of dissolved solids.This problem can be greatly reduced by using an inner argonstream that has been bubbled 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
44、 in the samplesolution uptake line. This action will isolate a potentialclogging problem prior to clogging 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 capill
45、ary and TFE-fluorocarbon (or otherpolymer) outer body to minimize or eliminate undesirable largedrop formation and facilitate HF tolerance (see Fig. 34,5). Atrue aerosol, as opposed to a mist, is produced consisting ofonly the desired smallest size droplets. Liquid uptake rates toproduce similar sen
46、sitivity to CGNs are sharply reduced withthe MCN. The MCN utilizes typical uptake rates of 0.1mL/min and is HF tolerant. Unusually small sample size, lowuptake rates, fast washout times, and very low drain ratescharacterize this nebulizer. The low uptake rate is particularly5Courtesy of CETAC Techno
47、logies, a division of Transgenomic Inc., 5600 S.42nd St., Omaha, NE.FIG. 2 Concentric Glass Nebulizer (CGN)2E1479 99 (2011)3beneficial for extending limited sample volumes so that thelong nebulization times encountered with sequential spectrom-eters undertaking multielement analysis may be successfu
48、llyaccomplished.7.3.2.2 The initial purchase cost is higher for the MCN thanfor the CGN but the cost may be 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 vo
49、lume inherentwith low sample uptake rates and significantly reduced drainrates. In addition, micro-autosamplers 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
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