ASTM D4628-97

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: D 4628 – 97
Standard Test Method for
Analysis of Barium, Calcium, Magnesium, and Zinc In
Unused Lubricating Oils By Atomic Absorption
Spectrometry
This standard is issued under the fixed designation D 4628; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
NOTE 2—Warning: Hazardous. Potentially toxic and explosive.
1. Scope
1.1 This test method is applicable for the determination of
3. Significance and Use
mass percent barium from 0.005 to 1.0 %, calcium and
3.1 Some oils are formulated with metal-containing addi-
magnesium from 0.002 to 0.3 %, and zinc from 0.002 to 0.2 %
tives that act as detergents, antioxidants, antiwear agents, etc.
in lubricating oils.
Some of these additives contain one or more of these metals:
1.2 Higher concentrations can be determined by appropriate
barium, calcium, zinc, and magnesium. This test method
dilution. Lower concentrations of metals such as barium,
provides a means of determining the concentration of these
calcium, magnesium, and zinc at about 10 ppm level can also
metals that gives an indication of the additive content in these
be determined by this test method. Use of this test method for
oils.
the determination at these lower concentrations should be by
agreement between the buyer and the seller.
4. Apparatus
1.3 Lubricating oils that contain viscosity index improvers
4.1 Atomic Absorption Spectrophotometer.
may give low results when calibrations are performed using
4.2 Analytical Balance.
standards that do not contain viscosity index improvers.
4.3 Automatic Measuring Pipet or Volumetric Class A Pipet,
1.4 The values stated in SI units are to be regarded as the
50-mL capacity.
standard.
4.4 Bottles with Screw Caps, 60 mL (2 oz).
1.5 This standard does not purport to address all of the
NOTE 3—Suitable volumetric flasks or plastic bottles may be substi-
safety concerns, if any, associated with its use. It is the
tuted.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4.5 Shaker, Mechanical Stirrer, or Ultrasonic Bath, capable
bility of regulatory limitations prior to use. Specific precau-
of handling 60-mL bottles.
tionary statements are given in Note 1, Note 5, and Note 7.
5. Reagents
2. Summary of Test Method
5.1 Base Oil, metal-free, with a viscosity of about 4 cSt at
2.1 A sample is weighed and base oil is added to 0.256
100°C. A100 neutral oil which provides good solvency for
0.01-g total mass. Fifty mililitres of a kerosine solution,
standards and additive concentrate is satisfactory. Highly
containing potassium as an ionization suppressant, are added,
paraffinic oils should be avoided.
and the sample and oil are dissolved. (Warning—See Note 2.)
5.2 2-Ethyl Hexanoic Acid, which has been determined to be
Standards are similarly prepared, always adding oil if neces-
free of interfering metals.
sary to yield a total mass of 0.25 g. These solutions are burned
5.3 Kerosine, Metal-Free (Note 4)—(See Note 5, Note 6,
in the flame of an atomic absorption spectrophotometer. An
and Warning Note 7), distillation range from 170°C to 280°C
acetylene/nitrous oxide flame is used. (Warning—See Note 1.)
at 100 kPa (1 atm). When the kerosine solvent is contaminated,
it may be purified metal-free by running through attapulgus
NOTE 1—Warning: Combustible. Vapor harmful.
clay.
NOTE 4—Solvents other than kerosene, such as xylene MEK and so
This test method is under the jurisdiction of ASTM Committee D-2 on
forth, may be used in this test method, however, the precision data quoted
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
in Section 16 was obtained using kerosene.
D02.03 on Elemental Analysis.
NOTE 5—Metal-free kerosine can be obtained from most laboratory
Current edition approved Nov. 10, 1997. Published June 1998. Originally
supply houses, but should be tested for metal content before using.
published as D 4628 – 86. Last previous edition D 4628 – 96a.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D4628–97
NOTE 6—Satisfactory results have been obtained in this test method by
5.5 Potassium Ionization Suppressant Solution—containing
using Baker “kerosine” (deodorized) which has typical initial and end
an oil-soluble potassium compound in kerosine at 2.0 6 0.1 g
boiling points of 191°C and 240°C, respectively, and a typical composi-
potassium/litre of solution.
tion of 96.7 volume % saturates, 0.1 volume % olefins, and a maximum
of 3.2 volume % aromatics. If the kerosine used by an operator deviates
NOTE 9—The actual potassium concentration needed varies with the
appreciably from this composition, there may be significant error.
source of potassium and perhaps the instrumental conditions as well. To
determine the needed concentration, atomize solutions containing 0, 500,
NOTE 7—Warning: Combustible. Vapor harmful.
1000, 1500, 2000, 2500, and 3000 ppm potassium with 25 ppm barium
5.4 Oil-Soluble Metal Compounds, stock standard blend in
and 5 ppm calcium in each. Plot graphs of barium and calcium absorbance
base oil. A0.25 6 0.01-g portion of this stock standard blend
versus potassium concentration as shown in Fig. 1. The minimum
concentration of potassium needed is that above the knee for both the
diluted with 50 mL of the potassium ionization suppressant
barium and calcium curves.
solution (see 5.5) shall yield a reading of 0.56 0.1 absorbance
units for each of the elements barium, calcium, magnesium,
5.6 Working Standards—Freshly prepared by weighing into
and zinc using a minimum of scale expansion or burner
six 60-mL bottles (1) 0.25, (2) 0.20, (3) 0.15, (4) 0.10, (5) 0.05,
rotation. The concentrations of the metal should be blended
and (6)0gof stock standard blend (see 5.4) to three significant
accurately to three significant figures. The actual concentra-
figures and add 0.0, 0.05, 0.10, 0.15, 0.20, and 0.25 6 0.01 g
tions should be chosen to conform to the optimum working
of base oil, respectively. Add 50 mL of potassium ionization
range of the particular instrument being used, but as a guide
suppressant solution (see 5.5) to each bottle and shake or stir to
one cooperator used 0.4 % barium, 0.03 % calcium, 0.03 %
dissolve.
magnesium, and 0.06 % zinc. The stock standard blend should
NOTE 10—Many modern AAS instruments can store up to 3 or 4
be heated and stirred to ensure a homogeneous solution.
calibration standards in memory. In such cases, follow the manufacturer’s
NOTE 8—In addition to the calibration standards identified in 5.4,
instructions, ensuring that the unknown sample’s absorbance is in the
single-element or multielement calibration standards may also be prepared
linear part of the calibration range used.
from materials similar to the samples being analyzed, provided the
calibration standards to be used have previously been characterized by
6. Sampling
independent, primary (for example, gravimetric or volumetric), and
6.1 Shake the sample thoroughly before sampling to ensure
analytical techniques to establish the elemental concentration mass
obtaining a representative sample.
percent levels.
7. Preparation of Apparatus
7.1 Consult the manufacturer’s instructions for the opera-
tion of the atomic absorption spectrophotometer. The present
Oil soluble metal compounds found satisfactory for this method are available
test method assumes that good operating procedures are
from National Institute of Standards and Technology, Office of Standard Reference
Materials, Washington, DC 20234.
FIG. 1 Plot Graphs for Barium and Calcium
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D4628–97
followed. Design differences between spectrophotometers 9. Procedure (Barium)
make it impractical to specify the required manipulations in
9.1 Weigh the sample to three significant figures into a
detail here.
60-mL (2-oz) bottle. The sample mass is chosen to give an
absorbance reading of 0.2 to 0.5. Add base oil to make 0.25 6
NOTE 11—Warning: Proper operating procedures are required for
safety as well as for reliability of results. An explosion can result from 0.01 g total mass. Add 50 mL of potassium suppressant
flame blow-back unless the correct burner head and operating sequence
solution, see 5.5, and dissolve. The maximum sample size to be
are used.
used is 0.25 g, and the minimum is 0.05 g.
9.1.1 To hazy samples add 0.25 6 0.01 mL of 2-ethyl
7.2 For the barium determination, fit the barium hollow
hexanoic acid and shake. If this clears up the haze, the analysis
cathode lamp and set the monochromator at 553.6 nm. Make
is run, and the dilution error is corrected by multiplyi
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