1、Designation: D 4628 05An American National StandardStandard Test Method forAnalysis of Barium, Calcium, Magnesium, and Zinc inUnused Lubricating Oils by Atomic AbsorptionSpectrometry1This standard is issued under the fixed designation D 4628; the number immediately following the designation indicate
2、s 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 (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of th
3、e Department of Defense.1. Scope*1.1 This test method is applicable for the determination ofmass percent barium from 0.005 to 1.0 %, calcium andmagnesium from 0.002 to 0.3 %, and zinc from 0.002 to 0.2 %in lubricating oils.1.2 Higher concentrations can be determined by appropriatedilution. Lower con
4、centrations of metals such as barium,calcium, magnesium, and zinc at about 10 ppm level can alsobe determined by this test method. Use of this test method forthe determination at these lower concentrations should be byagreement between the buyer and the seller.1.3 Lubricating oils that contain visco
5、sity index improversmay give low results when calibrations are performed usingstandards that do not contain viscosity index improvers.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to add
6、ress 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 warningstatements are given in 3.1, 6.3, and 8
7、.1.2. Referenced Documents2.1 ASTM Standards:D 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformance23. Summary of Test Method3.1 A sample is weighed and base oil is added to 0.25 60.01-g total mass. Fifty millilitres of a kerosine so
8、lution,containing potassium as an ionization suppressant, are added,and the sample and oil are dissolved. (WarningHazardous.Potentially toxic and explosive.) Standards are similarly pre-pared, always adding oil if necessary to yield a total mass of0.25 g. These solutions are burned in the flame of a
9、n atomicabsorption spectrophotometer. An acetylene/nitrous oxideflame is used. (WarningCombustible. Vapor harmful.)4. Significance and Use4.1 Some oils are formulated with metal-containing addi-tives that act as detergents, antioxidants, antiwear agents, etc.Some of these additives contain one or mo
10、re of these metals:barium, calcium, zinc, and magnesium. This test methodprovides a means of determining the concentration of thesemetals that gives an indication of the additive content in theseoils.5. Apparatus5.1 Atomic Absorption Spectrophotometer.5.2 Analytical Balance.5.3 Automatic Measuring P
11、ipet or Volumetric Class A Pipet,50-mL capacity.5.4 Bottles with Screw Caps, 60 mL (2 oz).NOTE 1Suitable volumetric flasks or plastic bottles may be substi-tuted.5.5 Shaker, Mechanical Stirrer, or Ultrasonic Bath, capableof handling 60-mL bottles.6. Reagents6.1 Base Oil, metal-free, with a viscosity
12、 of about 4 cSt at100C. A100 neutral oil which provides good solvency forstandards and additive concentrate is satisfactory. Highlyparaffinic oils should be avoided.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility
13、of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Nov. 1, 2005. Published November 2005. Originallyapproved in 1986. Last previous edition approved in 2002 as D 462802.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servicea
14、stm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
15、States.6.2 2-Ethyl HexanoicAcid, which has been determined to befree of interfering metals.6.3 Kerosine, Metal-FreeSee Notes 2-4.(WarningCombustible. Vapor harmful.) Distillation range from 170C to280C at 100 kPa (1 atm). When the kerosine solvent iscontaminated, it may be purified metal-free by run
16、ning throughattapulgus clay.NOTE 2Solvents other than kerosine, such as xylene MEK and soforth, may be used in this test method, however, the precision data quotedin Section 16 was obtained using kerosine.NOTE 3Metal-free kerosine can be obtained from most laboratorysupply houses, but should be test
17、ed for metal content before using.NOTE 4Satisfactory results have been obtained in this test method byusing Baker “kerosine” (deodorized) which has typical initial and endboiling points of 191C and 240C, respectively, and a typical composi-tion of 96.7 volume % saturates, 0.1 volume % olefins, and a
18、 maximumof 3.2 volume % aromatics. If the kerosine used by an operator deviatesappreciably from this composition, there may be significant error.6.4 Oil-Soluble Metal Compounds,3stock standard blend inbase oil. A 0.25 6 0.01-g portion of this stock standard blenddiluted with 50 mL of the potassium i
19、onization suppressantsolution (see 6.5) shall yield a reading of 0.5 6 0.1 absorbanceunits for each of the elements barium, calcium, magnesium,and zinc using a minimum of scale expansion or burnerrotation. The concentrations of the metal should be blendedaccurately to three significant figures. The
20、actual concentra-tions should be chosen to conform to the optimum workingrange of the particular instrument being used, but as a guideone cooperator used 0.4 % barium, 0.03 % calcium, 0.03 %magnesium, and 0.06 % zinc. The stock standard blend shouldbe heated and stirred to ensure a homogeneous solut
21、ion.NOTE 5In addition to the calibration standards identified in 6.4,single-element or multielement calibration standards may also be preparedfrom materials similar to the samples being analyzed, provided thecalibration standards to be used have previously been characterized byindependent, primary (
22、for example, gravimetric or volumetric), andanalytical techniques to establish the elemental concentration masspercent levels.6.5 Potassium Ionization Suppressant Solutioncontainingan oil-soluble potassium compound in kerosine at 2.0 6 0.1 gpotassium/litre of solution.NOTE 6The actual potassium conc
23、entration needed varies with thesource of potassium and perhaps the instrumental conditions as well. Todetermine the needed concentration, atomize solutions containing 0, 500,1000, 1500, 2000, 2500, and 3000 ppm potassium with 25 ppm bariumand 5 ppm calcium in each. Plot graphs of barium and calcium
24、 absorbanceversus potassium concentration as shown in Fig. 1. The minimumconcentration of potassium needed is that above the knee for both thebarium and calcium curves.6.6 Working StandardsFreshly prepared by weighing intosix 60-mL bottles (1) 0.25, (2) 0.20, (3) 0.15, (4) 0.10, (5) 0.05,and (6)0gof
25、stock standard blend (see 6.4) to three significantfigures and add 0.0, 0.05, 0.10, 0.15, 0.20, and 0.25 6 0.01 gof base oil, respectively. Add 50 mL of potassium ionizationsuppressant solution (see 6.5) to each bottle and shake or stir todissolve.NOTE 7Many modern AAS instruments can store up to 3
26、or 4calibration standards in memory. In such cases, follow the manufacturersinstructions, ensuring that the unknown samples absorbance is in thelinear part of the calibration range used.6.7 Quality Control (QC) Samples, preferably are portionsof one or more liquid petroleum materials that are stable
27、 and3Oil soluble metal compounds found satisfactory for this test method areavailable from National Institute of Standards and Technology, Office of StandardReference Materials, Washington, DC 20234.FIG. 1 Plot Graphs for Barium and CalciumD4628052representative of the samples of interest. These QC
28、samplescan be used to check the validity of the testing process asdescribed in Section 16.7. Sampling7.1 Shake the sample thoroughly before sampling to ensureobtaining a representative sample.8. Preparation of Apparatus8.1 Consult the manufacturers instructions for the opera-tion of the atomic absor
29、ption spectrophotometer. The presenttest method assumes that good operating procedures arefollowed. Design differences between spectrophotometersmake it impractical to specify the required manipulations indetail here. (WarningProper operating procedures are re-quired for safety as well as for reliab
30、ility of results. Anexplosion can result from flame blow-back unless the correctburner head and operating sequence are used.)8.2 For the barium determination, fit the barium hollowcathode lamp and set the monochromator at 553.6 nm. Makefine adjustments to the wavelength setting to give maximumoutput
31、. Using the correct burner head for acetylene/nitrousoxide, set up the acetylene/nitrous oxide flame. On instrumentswhere applicable, adjust the gain control to set this maximumat full scale, when aspirating standard (6)in6.6.8.3 Aspirate at about 2.5 to 3 mL/min a standard bariumsolution into the f
32、lame. Make adjustments to the height andangle of the burner and to the acetylene flow rate to givemaximum absorption. Make sure that standard (6)in6.6 stillgives zero absorbance by making adjustments, if necessary.9. Calibration (Barium)9.1 Aspirate standard (1)in6.6. With a minimum of scaleexpansio
33、n or burner rotation, obtain a reading of 0.5 6 0.1 onthe absorbance meter or alternative readout device.9.2 Aspirate the standards of 6.6 sequentially into the flameand record the output (or note the meter deflections). Aspiratethe solvent alone after each standard.9.3 Determine the net absorbance
34、of each standard. If thespectrophotometer output is linear in absorbance, the netabsorbance is given by the difference between the absorbancefor the standard or sample solution and the absorbance for thesolvent alone. If the spectrophotometer output is proportionalto transmission (that is, to light
35、intensity) then the net absor-bance is given by log10d0/d1, where the deflections are d0when solvent alone is aspirated and d1when the standard orsample solution is aspirated.9.4 Plot the net absorbance against the concentration (mg/50mL suppressant solution) of barium in the standards to give acali
36、bration curve.NOTE 8The calibration curve may be automatically calculated by theinstrument software and displayed by way of the instrument computerterminal, making actual plotting unnecessary.9.5 Calibration must be carried out prior to each group ofsamples to be analyzed and after any change in ins
37、trumentalconditions, as variation occurs in the instrument behavior.Readings may also vary over short times from such causes asbuildup of deposits on the burner slot or in the nebulizer. Thus,a single standard should be aspirated from time to time duringa series of samples to check whether the calib
38、ration haschanged (a check after every fifth sample is recommended).The visual appearance of the flame also serves as a usefulcheck to detect changes of condition.9.6 Determine the slope and intercept for barium based onthe calibration curve developed. The values will be used todetermine barium conc
39、entrations of samples to be tested.Ensure that the regression coefficient is at least 0.99 for barium,otherwise the laboratory needs to re-calibrate for barium whenthis criteria is not satisfied.10. Procedure (Barium)10.1 Weigh the sample to three significant figures into a60-mL (2-oz) bottle. The s
40、ample mass is chosen to give anabsorbance reading of 0.2 to 0.5. Add base oil to make 0.25 60.01 g total mass. Add 50 mL of potassium suppressantsolution, see 6.5, and dissolve. The maximum sample size to beused is 0.25 g, and the minimum is 0.05 g.10.1.1 To hazy samples add 0.25 6 0.01 mL of 2-ethy
41、lhexanoic acid and shake. If this clears up the haze, the analysisis run, and the dilution error is corrected by multiplying thefound results by 1.005. If the sample remains hazy, the sampleis not suitable to be analyzed by this test method.10.2 Samples yielding absorbances greater than 0.5 evenwith
42、 the minimum sample size can be accurately diluted withnew base oil to a suitable concentration. Make sure the newsolution is homogeneous before proceeding as instructed in10.1.10.3 Aspirate the sample solution and determine the absor-bance, aspirating solvent alone before and after each reading.11.
43、 Calculation (Barium)11.1 Read from the calibration curve the concentration, C,corresponding to the measured absorbance.C = concentration of barium in the diluted sample solution,mg/50 mL of suppressant solution.11.2 Calculate the barium content of the oils in percent massas follows:Barium, % mass 5
44、CD10W(1)where:W = grams of sample/50 mL,C = milligrams of metal/50 mL, andD = dilution factor if dilution was necessary in 10.2.NOTE 9If the calibration curve is linear, the concentration may bedetermined by an equation instead of a calibration curve.12. Calcium Determination12.1 Repeat Sections 7 t
45、hrough 10 replacing referencesmade to barium with calcium using the following conditions:12.1.1 Acetylene/nitrous oxide flame,12.1.2 Calcium hollow cathode lamp, and12.1.3 Analytical line 422.7 nm.13. Magnesium Determination13.1 Repeat Sections 7 through 10 replacing referencesmade to barium with ma
46、gnesium using the following condi-tions:D462805313.1.1 Acetylene/nitrous oxide flame,13.1.2 Magnesium hollow cathode lamp, and13.1.3 Analytical line 285.2 nm.14. Zinc Determination14.1 Repeat Sections 7 through 10 replacing referencesmade to barium with zinc using the following conditions:14.1.1 Ace
47、tylene/nitrous oxide flame,14.1.2 Zinc hollow cathode lamp, and14.1.3 Analytical line 213.9 nm.NOTE 10Although this test method has been described for thedetermination of four elements on a single sample, the sequence ofoperations in analyzing several samples should also be considered.Aspiration of
48、a sample to determine its absorbance is very quick.Changing wavelength setting and lamps takes longer. Thus, it is mosteconomical to make measurements at a single wavelength on a series ofsamples and standards before changing conditions.15. Report15.1 Report concentrations greater than 0.1 % to thre
49、esignificant figures.15.2 Concentrations between 0.0050.1 % barium and0.0020.1 % zinc, calcium, and magnesium are reported to twosignificant figures.15.3 Concentrations less than the lower limits in 15.2 shallbe reported as less than the appropriate lower limit.16. Quality Control16.1 Confirm the performance of the instrument or the testprocedure by analyzing a quality control (QC) sample (see6.7).16.1.1 When QC/Quality Assurance (QA) protocols arealready established in the testing facility, these may be usedwhen they confirm the reliability of the test resu
