1、Designation: D4628 16Standard 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 % to0.2 % in lubricating oils.1.2 Higher concentrations can be determined by appropriatedilution. Lower concentrations of metals
4、 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 viscosity index improversm
5、ay 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 asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety
6、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 8.1.2. Referenced Docum
7、ents2.1 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 g 60.01 g total mass. Fifty millilitres of a kerosene 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 similarlyprepared, always adding oil if necessary to yield a total mass of0.25 g. These solutions are burned in the flame of an
9、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 more
10、 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.4.2 Several additive metals and their compounds are addedto the lubricating oils to give beneficial pe
11、rformance. (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
12、Stirrer, or Ultrasonic Bath, capableof handling 60 mL bottles.6. Reagents6.1 Base Oil, metal-free, with a viscosity of about 4 cSt at100 C. A 100 neutral oil which provides good solvency for1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubr
13、icants and is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved Dec. 1, 2016. Published January 2017. Originallyapproved in 1986. Last previous edition approved in 2014 as D4628 14. DOI:10.1520/D4628-16.2For referenced ASTM standards, visit the ASTM websi
14、te, 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 Dr
15、ive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations i
16、ssued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1standards 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 Kerosene, Metal-FreeSee Notes 2-4.(Wa
17、rningCombustible. Vapor harmful.) Distillation range from 170 Cto 280 C at 100 kPa (1 atm). When the kerosene solvent iscontaminated, it may be purified metal-free by running throughattapulgus clay.NOTE 2Solvents other than kerosene, such as xylene MEK and soforth, may be used in this test method, h
18、owever, the precision data quotedin Section 16 was obtained using kerosene.NOTE 3Metal-free kerosene 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 “kerosene” (deod
19、orized) which has typical initial and endboiling points of 191 C and 240 C, respectively, and a typical compo-sition of 96.7 volume % saturates, 0.1 volume % olefins, and a maximumof 3.2 volume % aromatics. If the kerosene used by an operator deviatesappreciably from this composition, there may be s
20、ignificant error.6.4 Oil-Soluble Metal Compounds, stock standard blend inbase oil. A 0.25 g 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, ca
21、lcium, magnesium,and zinc 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
22、 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 solution.NOTE 5In addition to the calibration standards identified in 6.4,single-element or multielement calibration standards may
23、also be preparedfrom materials 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.
24、6.5 Potassium Ionization Suppressant Solutioncontainingan oil-soluble potassium compound in kerosene at 2.0 g 60.1 g potassium/litre of solution.NOTE 6The actual potassium concentration needed varies with thesource of potassium and perhaps the instrumental conditions as well. Todetermine the needed
25、concentration, atomize solutions containing 0 ppm,500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, and 3000 ppmpotassium with 25 ppm barium and 5 ppm calcium in each. Plot graphs ofbarium and calcium absorbance versus potassium concentration as shownin Fig. 1. The minimum concentration of potassium
26、needed is that abovethe knee for both the barium and calcium curves.6.6 Working StandardsFreshly prepared by weighing intosix 60 mL bottles (1) 0.25 g, (2) 0.20 g, (3) 0.15 g, (4) 0.10 g,(5) 0.05 g, and (6)0gofstock standard blend (see 6.4) to threesignificant figures and add 0.0 g, 0.05 g, 0.10 g,
27、0.15 g, 0.20 g,and 0.25 g 6 0.01 g of base oil, respectively. Add 50 mL ofpotassium ionization suppressant solution (see 6.5) to eachbottle and shake or stir to dissolve.NOTE 7Many modern AAS instruments can store up to 3 or 4calibration standards in memory. In such cases, follow the manufacturersin
28、structions, 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 andrepresentative of the samples of interest. These QC samplescan be used to
29、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 absorption spectrophotomete
30、r. 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 reliability of results. Anex
31、plosion 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. Using the correct bu
32、rner 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 mL min to 3 mL min a standardbarium solution into the flame. Make adju
33、stments to the heightand angle of the burner and to the acetylene flow rate to giveTABLE 1 Lubricants and Additive MaterialsElement Compounds Purpose/ApplicationBarium Sulfonates, phenates Detergent inhibitors, corrosion inhibitors, detergents, rustinhibitors, automatic transmission fluidsCalcium Su
34、lfonates, phenates Detergent inhibitors, dispersantsMagnesium Sulfonates, phenates Detergent inhibitorsZinc Dialkyldithiophosphates, dithiocarbamates,phenolates carboxylatesAnti-oxidant, corrosion inhibitors, antiwear additives,detergents, crankcase oils, hypoid gear lubricants, aircraftpiston engin
35、e oils, turbine oils, automatic transmissionfluids, railroad diesel engine oils, brake lubricantsD4628 162maximum 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 scale
36、expansion 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 abs
37、orbance 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, t
38、o 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 Plot the net absorbance against the concentration (mg/50 mL suppressant solution) of barium in the standards to g
39、ivea calibration 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 chan
40、ge 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 nebulizer. Thus,a single standard should be aspirated from time to time duringa series of samples to check whether
41、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 the slope and intercept for barium based onthe calibration curve developed. The values will be used todetermine ba
42、rium 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 is not satisfied.10. Procedure (Barium)10.1 Weigh the sample to three significant figures into a60 mL bottle. The
43、 sample mass is chosen to give an absorbancereading of 0.2 to 0.5. Add base oil to make 0.25 g 6 0.01 gtotal mass. Add 50 mL of potassium suppressant solution, see6.5, and dissolve. The maximum sample size to be used is0.25 g, and the minimum is 0.05 g.10.1.1 To hazy samples add 0.25 mL 6 0.01 mL of
44、 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 sampleis not suitable to be analyzed by this test method.10.2 Samples yielding absorbances greater than 0.5 e
45、venwith 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 theabsorbance, aspirating solvent alone before and after eachreading
46、.FIG. 1 Plot Graphs for Barium and CalciumD4628 16311. 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
47、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 the calibration curve is linear, the concentration may bedetermined by an equation instead of a calibration c
48、urve.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 Calcium hollow cathode lamp, and12.1.3 Analytical line 422.7 nm.13. Magnesium Determination13.1 Repeat Sections 7
49、 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 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 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 seque
