1、Designation: D7260 12Standard Practice forOptimization, Calibration, and Validation of InductivelyCoupled Plasma-Atomic Emission Spectrometry (ICP-AES)for Elemental Analysis of Petroleum Products andLubricants1This standard is issued under the fixed designation D7260; the number immediately followin
2、g the designation indicates the year oforiginal adoption or, in the 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. Scope*1.1 This practice cover
3、s information on the calibration andoperational guidance for the multi-element measurements us-ing inductively coupled plasma-atomic emission spectrometry(ICP-AES).1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the
4、 user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4307 Practice for Preparation of Liqui
5、d Blends for Use asAnalytical StandardsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6792 Practice for Quality System in Petroleum Productsand Lubricants Testing Laboratories2.2 ICP-AES Related Standards:
6、C1111 Test Method for Determining Elements in WasteStreams by Inductively Coupled Plasma-Atomic EmissionSpectroscopyC1109 Practice for Analysis of Aqueous Leachates fromNuclear Waste Materials Using Inductively CoupledPlasma-Atomic Emission SpectroscopyD1976 Test Method for Elements in Water by Indu
7、ctively-Coupled Argon Plasma Atomic Emission SpectroscopyD4951 Test Method for Determination ofAdditive Elementsin Lubricating Oils by Inductively Coupled PlasmaAtomicEmission SpectrometryD5184 Test Methods for Determination of Aluminum andSilicon in Fuel Oils by Ashing, Fusion, InductivelyCoupled P
8、lasma Atomic Emission Spectrometry, andAtomic Absorption SpectrometryD5185 Test Method for Determination of Additive Ele-ments, Wear Metals, and Contaminants in Used Lubricat-ing Oils and Determination of Selected Elements in BaseOils by Inductively Coupled Plasma Atomic EmissionSpectrometry (ICP-AE
9、S)D5600 Test Method for Trace Metals in Petroleum Coke byInductively Coupled Plasma Atomic Emission Spectrom-etry (ICP-AES)D5708 Test Methods for Determination of Nickel, Vana-dium, and Iron in Crude Oils and Residual Fuels byInductively Coupled Plasma (ICP) Atomic Emission Spec-trometryD6130 Test M
10、ethod for Determination of Silicon and OtherElements in Engine Coolant by Inductively CoupledPlasma-Atomic Emission SpectroscopyD6349 Test Method for Determination of Major and MinorElements in Coal, Coke, and Solid Residues from Com-bustion of Coal and Coke by Inductively CoupledPlasmaAtomic Emissi
11、on SpectrometryD6357 Test Methods for Determination of Trace Elementsin Coal, Coke, how-ever, the time lag between such homogenization and ICP-AESmeasurement should be kept to a minimum so that the particlesdo not settle out during the waiting period. Thus, for suchsamples autosampler may not be use
12、ful.6.3.3 To minimize nebulizer transport effects caused by highviscosity oils or viscosity improvers and additives in the oil,and to reduce potential spectral interferences, dilute thesamples and standards as appropriate to minimize transporteffects (minimum tenfold dilution). Both calibration stan
13、dardsand sample solutions should not contain more than 10 mass %oil. The calibration standards should be prepared with analyte-free oil added to the solution matrix such that all solutionscontain the same mass % oil. Also, when diluting samples togreater dilution factors, consistent oil to solvent r
14、atio should bemaintained. See 7.2 about the dilution solvents.6.3.4 Use of internal standard(s) could also be used in placeof dilution or standard additions. With samples containingacids, the biggest variation can actually be observed at low acidconcentrations.Acommon solution to this problem is to
15、ensurethat all samples and standards contain the same acid concen-tration (for example, 2 % nitric acid).6.3.5 Viscosity Index Improver EffectViscosity index im-provers that may be present in multi-grade lubricating oils, canbias the measurements.10However, these biases can be reducedto negligible p
16、roportion by using the above specified solvent-to-sample dilution or an internal standard, or both. Followinginternal standards have been successfully used in the labora-tories: Ag, Be, Cd, Co (most common), La, Mn, Pb, Sc, and Y.Often a viscosity index improver is included in the dilutingsolution t
17、o help reduce the effect on multi-grade oils.6.3.6 The use of an internal standard assumes the sample tocontain essentially no quantity of this internal standard element(see 8.8.4). This can be monitored by several means beyondanalysis of the sample beforehand to ascertain the un-dopedinternal stand
18、ard concentration. This may include the monitor-ing of multiple internal standard elements or comparison of theexpected magnitude of correction imposed by the internalstandard relative to a known or blank solution analyzed as asample.Also, the internal standard must be analyte-free as wellas free of
19、 concomitant species that may impose a spectralinterference on the analyte lines applied.6.4 Chemical Interferences:6.4.1 Chemical interferences are caused by molecular com-pound formation, ionization effects, and thermochemical ef-fects associated with sample vaporization and atomization inthe plas
20、ma. Normally these effects are not pronounced and canbe minimized by careful selection of operating conditions suchas incident power, plasma observation position, and so forth,by matrix matching, and by standard addition procedures.These types of interferences can be highly dependent on matrixtype a
21、nd the specific analyte.6.4.2 Selective volatilization can occur when the analyte ispresent in the sample in a relatively volatile form and canvaporize during the nebulization process. Whereas the trans-port efficiency of droplets produced from a standard pneumaticnebulizer is typically around 1 or
22、2 %, for vapor it can be muchhigher giving rise to enhanced results that can vary dependingon the relative concentrations of various chemical speciespresent in the sample (for example, volatile sulfur species suchas H2S, lead alkyls, and some silicon compounds).6.5 Salt buildup at the tip of the neb
23、ulizer can occur fromhigh dissolved solids (for example, in solutions prepared byalkali fusion with subsequent dilution with acids). This saltbuildup affects aerosol flow rate that can cause instrumentaldrift. To control this problem, in cases of aqueous analysisargon should be wetted prior to nebul
24、ization, using a tipwasher, or by diluting the sample.6.6 Carbon BuildupInspect the torch for carbon build-upduring the warm up period. If it occurs, replace the torchimmediately and consult the manufacturers operating guide totake proper steps to remedy the situation.6.6.1 Carbon that accumulates o
25、n the tip of the torchinjector tube can be removed by using nebulizer gas thatconsists of approximately 1 % oxygen in argon. However,oxygen absorbs radiation and cools the plasma that affects mostof the elements. Hence, it may not be a useful practice, exceptwhen high sensitivity for sodium is desir
26、ed.Also, oxygen in thenebulizer or auxiliary gas streams may defeat the purpose ofpurged optical path or vacuum for lines below 190 nm.6.6.2 The carbon buildup can also be cleaned off-line bybaking the torch in a furnace at 500C for 1 to 3 h dependingon the amount of carbon buildup.6.6.3 Generally,
27、carbon buildup can be minimized by reduc-ing the pump rate, adjusting the intermediate argon flow rate,using a chilled spray chamber, diluting the sample, adjustingthe torch vertically relative to the load coil, torch aerosol tipinternal diameter selection, or making other adjustments pos-sible desc
28、ribed in the instrument manufacturers instructionmanual. Consider also selection of diluent for organics (re-evaporation issue such as comparing solvents suggested belowof toluene versus xylenes versus kerosine. This considerationwill obviously be affected as well by volatility of samplematrix compo
29、nents that often may be safely evaporated prior todilution, as long as the analyte is not volatile. Often, increasingthe argon flow rate may be the only way to avoid carbonbuildup; other means do not work as well.10Bansal, J. B. and McElroy, F. C., “Accurate Elemental Analysis of MultigradeLubricati
30、ng Oils by ICP Method: Effect of Viscosity Modifiers,” SAE TechnicalPaper, 932694, 1993, pp. 6168.D7260 1256.7 Better control of the argon flow rate improves instru-ment performance. This control of the argon flow rate can beaccomplished with the use of mass flow controllers.7. Reagents and Material
31、s7.1 Base Oil, or other solvents used for diluting the samplesshould be free of analyte of interest and have a viscosity atroom temperature as close as possible to that of the samples tobe analyzed.7.1.1 Lubricating base oils can contain sulfur. For prepara-tion of sulfur standards and blending of a
32、dditive packages,white oil should be used.7.2 Dilution Solvents, Mixed xylenes, O-xylene, and kero-sine have been successfully used in the laboratories. Usereagent grade quality as a minimum. Select solvents and otherreagents that do not contain analytically significant levels ofthe analyte. Wavelen
33、gth scanning can indicate contaminatedreagents. For ICP-AES instruments that provide a visual profileof emission peaks, a check may be made of the solvent purityby aspirating the solvent and viewing the spectral regionswhere the element emissions of interest are to be found. Theabsence of emission p
34、eaks in these regions is evidence that thesolvent purity is satisfactory.7.3 Chemical stabilizers are often added to elemental stan-dard and blank solutions to keep the elements in a homogenousstable solution without precipitating out over long periods ofstorage.7.4 Water, acids, alkalies, and other
35、 chemicals used inpreparation of samples to convert them from organic toaqueous matrices should be of reagent quality at the minimum.7.5 Glassware, PlasticwareThese should be acid cleanedwith 10 % nitric acid (trace metal analysis grade) followed byseveral distilled or deionized water rinses. Glassw
36、are orplasticware that has previously contained solutions with highconcentration(s) of element(s) of interest must also be thor-oughly cleaned to remove trace analyte residues. This can beconfirmed by running analysis of blank matrix solutions storedovernight in the containers.8. Calibration8.1 Afte
37、r a warm-up time of at least 30 min, operate theinstrument according to the manufacturers instructions. Somemanufacturers recommend even longer warm-up periods tominimize changes in the slopes of the calibration curves.8.2 Wavelength ProfilingPerform any wavelength profil-ing that is specified in th
38、e normal operation of the instrument,if so equipped. Correct profiling is important to reveal spectralinterferences from high concentration of additive elements onthe spectral lines used for determining low levels of otherelements present.8.3 Calibrate the instrument by aspirating the blank andstand
39、ards. Allow at least 30 s aspiration beyond the point thatthe solution reaches the nebulizer to allow the instrument toequilibrate prior to signal integration. A total flush-out time ofapproximately 1.5 to 2 min should be allowed betweenstandards or following samples of comparably high or higherconc
40、entrations, during which diluent solvent is being aspirated.The computer establishes the slope, intercept, and correlationstatistics for each element.8.4 Often a two-point calibration is used. However, multiplecalibration standards may be used for obtaining improvedelement to signal correlation or v
41、alidate linearity of theconcentration range intended for use for a given analyte.8.5 To ensure the validity of calibration, check standardswith known elemental concentration should be used aftercalibration but before actually analyzing the unknown samples.It is recommended that the calibration blank
42、 and standards bematrix matched if possible with the same solvent, base oil, andso forth.8.6 To minimize physical interferences caused by changesin sample transport process (due to variations in sampleviscosity and concentration), it may be necessary to use aperistaltic pump in conjunction with cert
43、ain nebulizers. Inter-nal standard(s) could also be used instead of or as well asperistaltic pump.8.7 Background Correction:8.7.1 Ion-electron recombination and stray radiation giverise to background continuum. Introduction of an aerosol intothe plasma may affect the intensity of this background con
44、-tinuum. An additional recombination may also give rise tobackground continuum from dissolved major ions in thesample.8.7.2 Background correction generally involves measuringthe background emission at a wavelength near the analyticalwavelength (free of line emission from concomitant elements),and su
45、btracting that intensity from the total intensity measuredat the analytical wavelength. Selection of these correctionpoints should also be carefully considered so as not to fall onthe concomitant emission lines of elements potentially presentin the solutions being analyzed. Nor should any structured
46、spectral peaks be used (as opposed to flat baseline) for thiscorrection that might result from seemingly stable/consistentemission lines that may arise from matrix elements or argon.8.7.3 In some cases, if the background continuum intensityvaries with wavelength, it may be necessary to measure theba
47、ckground on both sides of the analytical wavelength andinterpolate to estimate the continuum intensity to be subtracted.8.8 Internal Standardization:8.8.1 Several ICP-AES test methods (see 2.2) require themandatory use of internal standard in analysis. This procedurerequires that every test solution
48、 (sample and standard) have thesame concentration (or a known concentration) of an internalstandard element that is not present in the original sample. Theinternal standard is usually combined with the dilution solventbecause this technique is common and efficient when preparingmany samples. However
49、, this assumes that the dilution solventwill be diluted with sample at a consistent ratio. For example,a tenfold dilution with an internal standard spiked solvent willrender a differing final internal standard concentration solutionthan a one hundred-fold dilution of this sample if the samedilution solvent is used. Though mathematical corrections maybe applied for the resulting disparate internal standard concen-tration in these solutions, analyte/internal standard free matrixadditives are frequently used to prepare such greater (onehundred-fold) dilutions and thus address this
