1、Designation: D4628 14Standard Test Method forAnalysis of Barium, Calcium, Magnesium, and Zinc inUnused Lubricating Oils by Atomic AbsorptionSpectrometry1This standard is issued under the fixed designation D4628; the number immediately following the designation indicates the year oforiginal adoption
2、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.This standard has been approved for use by agencies of the U.S. Department of Defense.1.
3、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 concentrations of metals such
4、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 viscosity index improversmay giv
5、e 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 asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concer
6、ns, 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 8.1.2. Referenced Documents2.
7、1 ASTM Standards:2D6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3. 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 solution,c
8、ontaining potassium as an ionization suppressant, are added,and the sample and oil are dissolved. (WarningHazardous.Potentially toxic and explosive.) Standards are similarlyprepared, always adding oil if necessary to yield a total mass of0.25 g. These solutions are burned in the flame of an atomicab
9、sorption 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 more of thes
10、e 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.4.2 Several additive metals and their compounds are addedto the lubricating oils to give beneficial performanc
11、e. (SeeTable 1.)5. Apparatus5.1 Atomic Absorption Spectrophotometer.5.2 Analytical Balance.5.3 Automatic Measuring Pipet or Volumetric ClassAPipet,50-mL capacity.5.4 Bottles with Screw Caps, 60 mL.NOTE 1Suitable volumetric flasks or plastic bottles may be substi-tuted.5.5 Shaker, Mechanical Stirrer,
12、 or Ultrasonic Bath, capableof handling 60-mL bottles.6. Reagents6.1 Base Oil, metal-free, with a viscosity of about 4 cSt at100C. A100 neutral oil which provides good solvency for1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and
13、 is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved Dec. 1, 2014. Published January 2015. Originallyapproved in 1986. Last previous edition approved in 2011 as D4628 05 (2011)1.DOI: 10.1520/D4628-14.2For referenced ASTM standards, visit the ASTM website
14、, 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Driv
15、e, PO Box C700, West Conshohocken, PA 19428-2959. United States1standards and additive concentrate is satisfactory. Highlyparaffinic oils should be avoided.6.2 2-Ethyl HexanoicAcid, which has been determined to befree of interfering metals.6.3 Kerosine, Metal-FreeSee Notes 2-4.(WarningCombustible. V
16、apor harmful.) Distillation range from 170C to280C at 100 kPa (1 atm). When the kerosine solvent iscontaminated, it may be purified metal-free by running throughattapulgus clay.NOTE 2Solvents other than kerosine, such as xylene MEK and soforth, may be used in this test method, however, the precision
17、 data quotedin Section 16 was obtained using kerosine.NOTE 3Metal-free kerosine can be obtained from most laboratorysupply houses, but should be tested for metal content before using.NOTE 4Satisfactory results have been obtained in this test method byusing Baker “kerosine” (deodorized) which has typ
18、ical 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 maximumof 3.2 volume % aromatics. If the kerosine used by an operator deviatesappreciably from this composition, there may be significant error.6.4 Oi
19、l-Soluble Metal Compounds ,3stock standard blendin base oil.A0.25 6 0.01-g portion of this stock standard blenddiluted with 50 mL of the potassium ionization 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
20、using a minimum of scale expansion or burnerrotation. The concentrations of the metal should be blendedaccurately to three significant figures. The actual concentra-tions should be chosen to conform to the optimum workingrange of the particular instrument being used, but as a guideone cooperator use
21、d 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 solution.NOTE 5In addition to the calibration standards identified in 6.4,single-element or multielement calibration standards may also be preparedfrom mater
22、ials similar to the samples being analyzed, provided thecalibration standards to be used have previously been characterized byindependent, primary (for example, gravimetric or volumetric), andanalytical techniques to establish the elemental concentration masspercent levels.6.5 Potassium Ionization S
23、uppressant Solutioncontainingan oil-soluble potassium compound in kerosine at 2.0 6 0.1 gpotassium/litre of solution.NOTE 6The actual potassium concentration needed varies with thesource of potassium and perhaps the instrumental conditions as well. Todetermine the needed concentration, atomize solut
24、ions 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 absorbanceversus potassium concentration as shown in Fig. 1. The minimumconcentration of potassium needed is that above the knee for both thebarium and
25、 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)0gofstock 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
26、 potassium ionizationsuppressant solution (see 6.5) to each bottle and shake or stir todissolve.NOTE 7Many modern AAS instruments can store up to 3 or 4calibration standards in memory. In such cases, follow the manufacturersinstructions, ensuring that the unknown samples absorbance is in thelinear p
27、art of the calibration range used.6.7 Quality Control (QC) Samples, preferably are portionsof one or more liquid petroleum materials that are stable andrepresentative of the samples of interest. These QC samplescan be used to check the validity of the testing process asdescribed in Section 16.7. Sam
28、pling7.1 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 absorption spectrophotometer. The presenttest method assumes that good operating procedures arefollow
29、ed. 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 reliability of results. Anexplosion can result from flame blow-back unless the correctburner head and
30、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. Using the correct burner head for acetylene/nitrousoxide, set up the acetylene/nitrous oxide f
31、lame. On instrumentswhere applicable, adjust the gain control to set this maximumat full scale, when aspirating standard (6)in6.6.3Oil soluble metal compounds found satisfactory for this test method areavailable from National Institute of Standards and Technology, Office of StandardReference Materia
32、ls, Washington, DC 20234.TABLE 1 Lubricants and Additive MaterialsElement Compounds Purpose/ApplicationBarium Sulfonates, phenates Detergent inhibitors, corrosion inhibitors, detergents, rustinhibitors, automatic transmission fluidsCalcium Sulfonates, phenates Detergent inhibitors, dispersantsMagnes
33、ium Sulfonates, phenates Detergent inhibitorsZinc Dialkyldithiophosphates, dithiocarbamates,phenolates carboxylatesAnti-oxidant, corrosion inhibitors, antiwear additives,detergents, crankcase oils, hypoid gear lubricants, aircraftpiston engine oils, turbine oils, automatic transmissionfluids, railro
34、ad diesel engine oils, brake lubricantsD4628 1428.3 Aspirate at about 2.5 to 3 mL/min a standard bariumsolution into the flame. 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
35、by making adjustments, if necessary.9. Calibration (Barium)9.1 Aspirate standard (1)in6.6. With a minimum of scaleexpansion 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 t
36、he output (or note the meter deflections). Aspiratethe solvent alone after each standard.9.3 Determine the net absorbance 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 a
37、nd the absorbance for thesolvent alone. If the spectrophotometer output is proportionalto transmission (that is, to light 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
38、 Plot the net absorbance against the concentration (mg/50mL suppressant solution) of barium in the standards to give acalibration curve.NOTE 8The calibration curve may be automatically calculated by theinstrument software and displayed by way of the instrument computerterminal, making actual plottin
39、g unnecessary.9.5 Calibration must be carried out prior to each group ofsamples to be analyzed and after any change in instrumentalconditions, 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 ne
40、bulizer. Thus,a single standard should be aspirated from time to time duringa series of samples to check whether the calibration 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 t
41、he slope and intercept for barium based onthe calibration curve developed. The values will be used todetermine barium concentrations 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
42、is not satisfied.10. Procedure (Barium)10.1 Weigh the sample to three significant figures into a60-mLbottle. The sample mass is chosen to give an absorbancereading of 0.2 to 0.5. Add base oil to make 0.25 6 0.01 g totalmass. Add 50 mL of potassium suppressant solution, see 6.5,and dissolve. The maxi
43、mum sample size to be used 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-ethylhexanoic 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 sa
44、mpleis not suitable to be analyzed by this test method.10.2 Samples yielding absorbances greater than 0.5 evenwith 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.FIG. 1 Pl
45、ot Graphs for Barium and CalciumD4628 14310.3 Aspirate the sample solution and determine theabsorbance, aspirating solvent alone before and after eachreading.11. Calculation (Barium)11.1 Read from the calibration curve the concentration, C,corresponding to the measured absorbance.C = concentration o
46、f 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 5CD10W(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 th
47、e calibration curve is linear, the concentration may bedetermined by an equation instead of a calibration curve.12. Calcium Determination12.1 Repeat Sections 7 through 10 replacing referencesmade to barium with calcium using the following conditions:12.1.1 Acetylene/nitrous oxide flame,12.1.2 Calciu
48、m 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 magnesium using the following condi-tions:13.1.1 Acetylene/nitrous oxide flame,13.1.2 Magnesium hollow cathode lamp, and13.1.3 Analytical lin
49、e 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 Acetylene/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 a sample to determine its absorbance is very quick.Changing wavelength setting and lamps takes longer. Thus,
