ASTM E1770-2014 Standard Practice for Optimization of Electrothermal Atomic Absorption Spectrometric Equipment《电热原子吸收光谱仪器优化的标准实践规程》.pdf

1、Designation: E1770 14Standard Practice forOptimization of Electrothermal Atomic AbsorptionSpectrometric Equipment1This standard is issued under the fixed designation E1770; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o

2、f 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 the optimization of electrothermalatomic absorption spectrometers and the checking of spectrom-

3、eter performance criteria.1.2 The values stated in SI units are to be regarded as thestandard.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 pra

4、ctices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated MaterialsE135 Terminology Relating to Analytical Chemistry for

5、Metals, Ores, and Related MaterialsE876 Practice for Use of Statistics in the Evaluation ofSpectrometric Data (Withdrawn 2003)3E1184 Practice for Determination of Elements by GraphiteFurnace Atomic Absorption SpectrometryE1452 Practice for Preparation of Calibration Solutions forSpectrophotometric a

6、nd for Spectroscopic Atomic Analy-sis (Withdrawn 2005)33. Terminology3.1 For definitions of terms used in this test method, refer toTerminology E135.4. Significance and Use4.1 This practice is for optimizing the parameters used inthe determination of trace elements in metals and alloys by theelectro

7、thermal atomic absorption spectrometric method. It alsodescribes the practice for checking the spectrometer perfor-mance. The work is expected to be performed in a properlyequipped laboratory by trained operators and appropriatedisposal procedures are to be followed.5. Apparatus5.1 Atomic Absorption

8、 Spectrometer with ElectrothermalAtomizer, equipped with an appropriate background corrector,a signal output device such as a video display screen (VDS), adigital computer, a printer, and an autosampler.5.2 Pyrolytic Graphite-Coated Graphite Tubes, conformingto the instrument manufacturers specifica

9、tions.5.3 Pyrolytic Graphite Platforms, Lvov design, fitted to thetubes specified in 5.2.5.4 Pyrolytic Graphite-Coated Graphite Tubes,platformless, conforming to the instrument manufacturersspecifications.5.5 Radiation Source for the AnalyteA hollow cathodelamp or electrodeless discharge lamp is sui

10、table.NOTE 1The use of multi-element lamps is not generallyrecommended, since they may be subject to spectral line overlaps.5.6 For general discussion of the theory and instrumentalrequirements of electrothermal atomic absorption spectromet-ric analysis, see Practice E1184.6. Reagents6.1 Purity and

11、Concentration of ReagentsThe purity andconcentration of common chemical reagents shall conform toPractices E50. The reagents should be free of or containminimal amounts (0.01 g/g) of the analyte of interest.6.2 Magnesium Nitrate Solution 2 g/L Mg(NO3)2Dissolve 0.36 6 0.01 g high-purity Mg(NO3)26H2O

12、in about50 mL of water, in a 100-mL beaker, and transfer the solutioninto a 100-mL volumetric flask. Dilute to mark with water and1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommit

13、tee E01.20 on Fundamental Practices.Current edition approved Dec. 1, 2014. Published February 2015. Originallyapproved in 1995. Last previous edition approved in 2006 as E1770 95 (2006).DOI: 10.1520/E1770-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custome

14、r Service at 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, Wes

15、t Conshohocken, PA 19428-2959. United States1mix. Store in polypropylene or high-density polyethylenebottle. Alternatively, this solution may be purchased from acommercial supplier.6.3 Calibration SolutionsRefer to the preparation of cali-bration solutions in the relevant analytical method for thede

16、termination of trace elements in the specific matrix. Calibra-tion solution S0represents the calibration solution containingno analyte; S1the least concentrated calibration solution; S2thecalibration solution with the next highest concentration;through Sk, the most concentrated calibration solution.

17、 Alsorefer to Practice E1452.6.4 Matrix ModifiersRefer to the relevant analyticalmethod for the determination of trace elements in the specificmatrix.7. Initial Checks and Adjustments7.1 Turn on power, cooling water, gas supplies, and fumeexhaust system as required for the instrument being used.7.2

18、Open the furnace to inspect the tube and contacts.Replace graphite components, if wear or contamination isevident. Inspect windows and clean or replace as required.7.2.1 New graphite contacts or new tubes should be condi-tioned prior to use, in accordance with the heating programrecommended by the m

19、anufacturer.7.2.1.1 In the absence of manufacturers recommendations,a conditioning program for a graphite furnace is shown inTable 1.8. Radiation Source8.1 Install and operate hollow cathode lamps or electrode-less discharge lamps in accordance with the manufacturersinstructions.8.2 After the manufa

20、cturers prescribed warm-up time, thesignal from the radiation source should not deviate by morethan 0.5 % from the maximum value (that is, by not more than0.002 absorbance units) over a period of 15 min. Significantlygreater fluctuations are usually indicative of a faulty lamp orpower supply.9. Spec

21、trometer Parameters9.1 Wavelength, as specified by the appropriate procedure.9.2 Slit Width, as recommended by the manufacturer. Wheretwo slit width settings are available, select the shorter width.9.3 Background Correction:9.3.1 Zeeman Background Correction System:9.3.1.1 Ensure that the poles of t

22、he magnet are clean andsecurely tightened.9.3.1.2 If necessary, set the optical temperature sensor inaccordance with the instrument manufacturers instructions.9.3.2 Continuum Background System:9.3.2.1 Select the background correction option and allowlamps to stabilize for 30 min. Verify that the ene

23、rgies of theanalyte lamp and the deuterium lamp are balanced withintolerances recommended by the manufacturer.9.3.2.2 If necessary, set the optical temperature sensor inaccordance with the instrument manufacturers recommenda-tion.9.3.3 To check the performance of the background correc-tion system, m

24、easure the atomic background absorbance of 20L of 2 g/L magnesium nitrate solution at a wavelength in the200 to 250 nm region (for example, Bi 223.1 nm) using a drytemperature of 120C, a pyrolysis temperature of 950C, andan atomization temperature of 1800C. A large backgroundsignal should be observe

25、d with no over-or under-correction ofthe atomic signal.NOTE 2In general, Zeeman systems should compensate for back-ground levels as high as 1.0 to 1.5 absorbance units. A continuumcorrection system should be able to correct for the broad-band backgroundabsorbance up to 0.5 to 0.6 absorbance units.9.

26、4 AutosamplerCheck operation of the autosampler. Payparticular attention to the condition of the pipette tip andposition of the tip during sample deposition. Clean the pipettetip with methanol. Adjust in accordance with the manufactur-ers instructions.NOTE 3Use of an appropriate surfactant in the ri

27、nse water mayenhance operation. If a surfactant is used, it should be checked for thepresence of all the analytes to be determined.10. Optimization of the Furnace Heating Program10.1 Optimization of the furnace heating program is essen-tial. Furnace programs recommended by the manufacturers areoften

28、 designed for samples of a completely unrelated matrix.The analyst shall optimize the furnace program for a particularsample matrix (for example, steel, nickel alloys, etc.) andmodifier system in accordance with the following procedure:Furnace Step SectionDrying 10.2Pyrolysis 10.3Atomization 10.4Cle

29、an-out 10.510.2 Drying Step:10.2.1 Select the graphite tube type (Lvov or platformless)and measurement mode (peak height or integrated peak area).Then select the same heating parameters used in 9.3.3. Opti-mize the drying parameters using any of the calibrationsolutions (see 6.3) and the procedure g

30、iven in either 10.2.2 or10.2.3.10.2.2 Samples Deposited on the Tube WallFor wall-deposited samples, a drying temperature of 120C is satisfac-tory. To avoid spattering, a 20 s ramping time should be usedto reach the 120C temperature and then held at that tempera-ture. The holding time will depend on

31、the volume of the sampleintroduced. Typical holding times are as follows:TABLE 1 Program for Graphite Furnace ConditioningStep Temperature, C Ramp, s Hold, sGas flow, mL/min1 1500 60 20 3002 20 1 10 3003 2000 60 20 3004 20 1 10 3005 2600 60 10 3006 20 1 10 3007 2650 2 5 0E1770 142Injected Volume, L

32、Holding Time, s10 1540 3010.2.3 Samples Deposited on the Lvov Platform:10.2.3.1 When using a Lvov platform, a two-stage dryingprocess is beneficial to prevent spattering.10.2.3.2 In the first stage, heat the sample rapidly to 80C,usinga1sramp and then hold the temperature at 80C for ashort time. The

33、 holding time depends upon the volume of thesolution injected. Typical holding times are shown in 10.2.2.10.2.3.3 For the second stage, the temperature is rampedover a period of 20 to 30 s, to a value 20 to 40C above theboiling point of the solvent. The holding times should be thesame as given in 10

34、.2.3.2.10.2.4 In both cases, select a preliminary set of dryingconditions and monitor the drying process visually with the aidof a dental mirror, to ensure that it proceeds without spattering.Hold the mirror directly above the sample introduction port(avoid touching the magnet), or near the end wind

35、ows of thegraphite tube. Observe vapor formation on the mirror as dryingproceeds. Vapor evolution should cease at approximately 10 sbefore the end of the drying step. Adjust the hold timesaccordingly to accomplish this.10.2.4.1 Warning:To prevent serious eye injury, do notview the tube directly duri

36、ng the atomization or clean-outsteps.10.3 Pyrolysis Step:10.3.1 During this step, volatile components of the matrixare driven off and precursory reactions occur (for example,reduction of the analyte oxide to the elemental state and theformation of matrix refractory oxides and carbides).NOTE 4Because

37、 of the low volatility of most metal alloy matrices,most of the matrix will remain in the furnace after the pyrolysis.10.3.2 Use the optimum drying conditions as determined in10.2.NOTE 5At this stage, both the optimum pyrolysis and atomizationtemperatures are unknown. An estimate of the suitable ato

38、mizationtemperature shall be made and entered into the instrument prior tooptimization of the pyrolysis temperature.10.3.3 Set atomizing temperature according to the manufac-turers instructions. Select the “Gas Interrupt” (or “Gas Stop”)option. Select an atomization integration time of 10 s.10.3.4 S

39、elect a pyrolysis time of 30 s ramp and 30 s hold.10.3.5 Select a calibration solution (see 6.3) which will givean absorbance reading of 0.2 to 0.4 absorbance units.10.3.6 Vary the pyrolysis temperature in increments of100C, throughout the range from 500 to 1400C, taking threeabsorbance measurements

40、 at each step for the calibrationsolution selected in accordance with 10.3.5.10.3.7 Calculate the mean of the three absorbance measure-ments obtained for each temperature step. Plot a graph relatingthe pyrolysis temperature to the mean absorbance. Note thetemperature at which the absorbance starts t

41、o decline. Subtract50C from this value to obtain the optimum pyrolysis tempera-ture.NOTE 6The 50C allowance accommodates the day-to-day variationsin the working temperature of the system.10.3.8 Use the optimum pyrolysis temperature found, andvary the hold time over the range of 15 to 60 s (15 s inte

42、rvals).Take three absorbance measurements at each step for thecalibration solution selected in accordance with 10.3.5. Moni-tor the background signal during the process, and note the timeat which the background signal returns to the baseline.10.3.9 Calculate the mean of the three absorbance measure-

43、ments. There should be no evidence of analyte loss (indicatedby lower absorbances for the longer hold times).10.3.10 Provided the pyrolysis condition in 10.3.7 issatisfied, select the shortest time in which the backgroundsignal returns to the baseline and add 10 s to this value toobtain the optimum

44、hold time.NOTE 7A slow ramp time of 30 s and a hold time of 30 s is usuallysufficient for all pretreatment reactions to occur. Short ramp times mayprovoke explosive loss of sample in the tube.10.4 Atomization Step:10.4.1 This step involves the production of gaseous analyteatoms inside the graphite t

45、ube.10.4.2 The analyst should determine the optimum atomiza-tion temperature and integration time experimentally, using thesame “Gas Interrupt option,” graphite tube type, and measuringmode combination selected before the optimization of thedrying step.NOTE 8Although it is possible to optimize the L

46、vov platform usingthe peak height measurement mode, the atomization step shall beoptimized in such a manner that the conditions required for stabilizedtemperature platform furnace (STPF) operation are satisfied. In addition tothe use of “Gas Interrupt” and matrix modification (inherent in certainpro

47、cedures), the following additional conditions are to be satisfied: (1) Thetemperature difference between the pyrolysis step and the atomization stepshould be as small as possible (less than 1000C). This allows the furnaceto approach the near isothermal conditions quickly and reduces theamount of mat

48、rix volatilized; (2) Peak area integration measurement modeshall be used; and (3) There shall be zero ramping time between thepyrolysis and the atomization steps. The “Gas Interrupt” will interrupt theflow of inert gas through the graphite tube from a few seconds prior to thestart of the atomization

49、 cycle to the end of the atomization cycle.10.4.3 Use the optimum drying and pyrolysis conditions.10.4.4 Select an atomization temperature of 1200C and anintegration time of 20 s.10.4.5 Obtain three absorbance measurements with thecalibration solution used in 10.3.5.10.4.6 Repeat varying the atomization temperature in 100Cincrements up to 2500C. It is not necessary to continue raisingthe atomization temperature once the absorbance reaches aplateau.10.4.7 Plot the mean of the three absorbance measurementsobtained for each step again