ASTM D4951-00
(Test Method)Standard Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry
Standard Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry
SCOPE
1.1 This test method covers the quantitative determination of barium, boron, calcium, copper, magnesium, phosphorus, sulfur, and zinc in unused lubricating oils and additive packages.
1.2 The precision statements are valid for dilutions in which the mass % sample in solvent is held constant in the range of 1 to 5 mass % oil.
1.3 The precision tables define the concentration ranges covered in the interlaboratory study. However, both lower and higher concentrations can be determined by this test method. The low concentration limits are dependent on the sensitivity of the ICP instrument and the dilution factor. The high concentration limits are determined by the product of the maximum concentration defined by the linear calibration curve and the sample dilution factor.
1.4 Sulfur can be determined if the instrument can operate at a wavelength of 180 nm.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 4951 – 00 An American National Standard
Standard Test Method for
Determination of Additive Elements in Lubricating Oils by
Inductively Coupled Plasma Atomic Emission Spectrometry
This standard is issued under the fixed designation D 4951; 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.
1. Scope Magnesium, and Zinc in Unused Lubricating Oils by
Atomic Absorption Spectrometry
1.1 This test method covers the quantitative determination
D 4927 Test Methods for Elemental Analysis of Lubricant
of barium, boron, calcium, copper, magnesium, phosphorus,
and Additive Components—Barium, Calcium, Phospho-
sulfur, and zinc in unused lubricating oils and additive pack-
rus, Sulfur, and Zinc by Wavelength-Dispersive X-Ray
ages.
Fluorescence Spectroscopy
1.2 The precision statements are valid for dilutions in which
D 5185 Test Method for Determination of Additive Ele-
the mass % sample in solvent is held constant in the range of
ments, Wear Metals, and Contaminants in Used Lubricat-
1 to 5 mass % oil.
ing Oils and Determination of Selected Elements by
1.3 The precision tables define the concentration ranges
Inductively Coupled Plasma Atomic Emission Spectrom-
covered in the interlaboratory study. However, both lower and
etry
higher concentrations can be determined by this test method.
D 6299 Practice for Applying Statistical Quality Assurance
The low concentration limits are dependent on the sensitivity
Techniques to Evaluate Analytical Measurement System
of the ICP instrument and the dilution factor. The high
Performance
concentration limits are determined by the product of the
maximum concentration defined by the linear calibration curve
3. Summary of Test Method
and the sample dilution factor.
3.1 A sample portion is weighed and diluted by mass with
1.4 Sulfur can be determined if the instrument can operate at
mixed xylenes or other solvent. An internal standard, which is
a wavelength of 180 nm.
required, is either weighed separately into the test solution or is
1.5 The values stated in SI units are to be regarded as the
previously combined with the dilution solvent. Calibration
standard. The values given in parentheses are for information
standards are prepared similarly. The solutions are introduced
only.
to the ICP instrument by free aspiration or an optional
1.6 This standard does not purport to address all of the
peristaltic pump. By comparing emission intensities of ele-
safety concerns, if any, associated with its use. It is the
ments in the test specimen with emission intensities measured
responsibility of the user of this standard to establish appro-
with the calibration standards and by applying the appropriate
priate safety and health practices and determine the applica-
internal standard correction, the concentrations of elements in
bility of regulatory limitations prior to use.
the sample are calculable.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
4.1 This test usually requires several minutes per sample.
D 1552 Test Method for Sulfur in Petroleum Products
2 This test method covers eight elements and thus provides more
(High-Temperature Method)
elemental composition data than Test Method D 4628 or Test
D 4057 Practice for Manual Sampling of Petroleum and
3 Method D 4927. In addition, this test method provides more
Petroleum Products
accurate results than Test Method D 5185, which is intended
D 4307 Practice for Preparation of Liquid Blends for Use as
3 for used lubricating oils and base oils.
Analytical Standards
4.2 Additive packages are blends of individual additives,
D 4628 Test Method for Analysis of Barium, Calcium,
which can act as detergents, antioxidants, antiwear agents, etc.
Many additives contain one or more elements covered by this
This test method is under the jurisdiction of ASTM Committee D-2 on
test method. Additive package specifications are based, in part,
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
on elemental composition. Lubricating oils are typically blends
D02.03 on Elemental Analysis.
Current edition approved Jan. 10, 2000. Published March 2000. Originally
published as D 4951 – 89. Last previous edition D 4951 – 96.
2 4
Annual Book of ASTM Standards, Vol 05.01. Annual Book of ASTM Standards, Vol 05.03.
3 5
Annual Book of ASTM Standards, Vol 05.02. Annual Book of ASTM Standards, Vol 05.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 4951
of additive packages, and their specifications are also deter- 6.7 Ultrasonic Homogenizer, Optional—A bath-type or
mined, in part, by elemental composition. This test method can probe-type ultrasonic homogenizer can be used to homogenizer
be used to determine if additive packages and unused lubricat- the test specimen.
ing oils meet specifications with respect to elemental compo-
sition. 7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be
5. Interferences
used in all tests. Unless otherwise indicated, it is intended that
5.1 Spectral—There are no known spectral interferences
all reagents conform to the specifications of the Committee on
between elements covered by this test method when using the
Analytical Reagents of the American Chemical Society where
spectral lines listed in Table 1. However, if spectral interfer-
such specifications are available.
7.2 Base Oil, U.S.P. white oil, or a lubricating base oil that
A
is free of analytes, with a viscosity of about 4 cSt at 100°C.
TABLE 1 Elements Determined and Suggested Wavelengths
(Warning—Lubricating base oils can contain sulfur. For
Element Wavelength, nm
preparation of sulfur standards and blending of additive pack-
Barium 233.53, 455.40, 493.41
B ages, white oil is recommended.)
Boron 182.59, 249.68
Calcium 315.88, 317.93, 364.4, 422.67 7.3 Internal Standard, (Required)—An oil-soluble internal
Copper 324.75
standard element is required. The following internal standards
Magnesium 279.08, 279.55, 285.21
B were successfully used in the interlaboratory study on preci-
Phosphorus 177.51, 178.29, 213.62, 214.91, 253.40
B
Sulfur 180.73, 182.04, 182.62 sion: Ag, Be, Cd, Co (most common), La, Mn, Pb, Y.
Zinc 202.55, 206.20, 213.86, 334.58, 481.05
7.4 Organometallic Standards—Multi-element standards,
A
These wavelengths are only suggested and do not represent all possible
containing known concentrations (approximately 0.1 mass %)
choices.
B of each element, can be prepared from the individual metal
Wavelengths for boron, phosphorus, and sulfur below 190 nm require that a
vacuum or inert gas purged optical path be used. concentrates. Refer to Practice D 4307 for a procedure for
preparation of multicomponent liquid blends. When preparing
multi-element standards, be certain that proper mixing is
ences exist because of other interfering elements or selection of
achieved. Commercially available multi-element blends (with
other spectral lines, correct for the interference using the
known concentrations of each element at approximately 0.1
technique described in Test Method D 5185.
mass %) are also satisfactory.
5.2 Viscosity Index Improver Effect—Viscosity index im-
7.4.1 More than one multi-element standard can be neces-
provers, which can be present in multi-grade lubricating oils,
sary to cover all elements, and the user of this test method can
can bias measurements. However, the biases can be reduced to
select the combination of elements and their concentrations in
negligible proportion by using the specified solvent-to-sample
the multi-element standards. It can be advantageous to select
dilution and an internal standard.
concentrations that are typical of unused oils. However, it is
imperative that concentrations are selected such that the
6. Apparatus
emission intensities measured with the working standards can
6.1 Inductively-Coupled Plasma Atomic Emission
be measured precisely (that is, the emission intensities are
Spectrometer—Either a sequential or simultaneous spectrom-
significantly greater than background) and that these standards
eter is suitable, if equipped with a quartz ICP torch and r-f
represent the linear region of the calibration curve. Frequently,
generator to form and sustain the plasma.
the instrument manufacturer publishes guidelines for determin-
6.2 Analytical Balance, capable of weighing to 0.001 g or
ing linear range.
0.0001 g, capacity of 150 g.
7.4.2 Some commercially available organometallic stan-
6.3 Peristaltic Pump, (Recommended)—A peristaltic pump
dards are prepared from metal sulfonates and therefore contain
is strongly recommended to provide a constant flow of solu-
sulfur. For sulfur determinations, a separate sulfur standard can
tion. The pumping speed must be in the range 0.5 to 3 mL/min.
be required. A sulfur standard can be prepared by blending
The pump tubing must be able to withstand at least 6 h
NIST SRM 1622 with white oil.
exposure to the dilution solvent. Fluoroelastomer copolymer
7.4.3 Metal sulfonates can be used as a sulfur standard if the
tubing is recommended.
sulfur content is known or determined by an appropriate test
6.4 Solvent Dispenser, (Optional)—A solvent dispenser
method such as Test Method D 1552.
calibrated to deliver the required weight of diluent can be
7.4.4 Petroleum additives can also be used as organometal-
advantageous. Ensure that solvent drip does not affect accu-
lic standards if their use does not adversely affect precision nor
racy.
introduce significant bias.
6.5 Specimen Solution Containers, 30 to 120 mL, glass or
polyolefin vials or bottles, with screw caps.
6.6 Vortexer, (Optional)—Vortex the sample plus diluent
Reagent Chemicals, American Chemical Society Specifications, American
mixture until the sample is completely dissolved.
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Fluoroelastomer copolymer is manufactured as Viton, a trademark owned by E. and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
I. duPont de Nemours. MD.
D 4951
7.5 Dilution Solvent—Mixed xylenes, o-xylene, and kero- 10.3 ICP Excitation Source—Initiate the plasma source at
sine were successfully used in the interlaboratory study on least 30 min before performing an analysis. During this warm
precision. up period, nebulize dilution solvent. Inspect the torch for
carbon build-up during the warm up period. If carbon build-up
8. Internal Standardization (Required)
occurs, replace the torch immediately and consult the manu-
8.1 The internal standard procedure requires that every test facturer’s operating guide to take proper steps to remedy the
solution (sample and standard) have the same concentration (or situation.
a known concentration) of an internal standard element that is
NOTE 2—Carbon that accumulates on the tip of the torch injector tube
not present in the original sample. The internal standard is
can be removed by using nebulizer gas that consists of approximately 1 %
usually combined with the dilution solvent. Internal standard
oxygen in argon.
compensation is typically handled in one of two different ways,
10.3.1 Generally, carbon build-up can be minimized by
which can be summarized as follows.
increasing the intermediate argon flow rate or lowering the
8.1.1 Calibration curves are based on the measured intensity
torch, or both, relative to the load coil.
of each analyte divided (that is, scaled) by the measured
NOTE 3—Some manufacturers recommend even longer warm up peri-
intensity of the internal standard per unit internal standard
ods to minimize changes in the slopes of the calibration curves.
element concentration. Concentrations for each analyte in the
test specimen solution are read directly from these calibration
10.4 Wavelength Profiling—Perform any wavelength profil-
curves.
ing that is specified in the normal operation of the instrument.
8.1.2 For each analyte and the internal standard element,
10.5 Operating Parameters—Assign the appropriate oper-
calibration curves are based on measured (unscaled) intensi- ating parameters to the instrument task file so that the desired
ties. Uncorrected concentrations for each analyte in the test
elements can be determined. Parameters to be included are
specimen solution are read from these calibration curves. element, wavelength, background correction points (optional),
Corrected analyte concentrations are calculated by multiplying
interelement correction factors (refer to 5.1), integration time,
the uncorrected concentrations by a factor equal to the actual
and internal standard compensation (required). Multiple inte-
internal standard concentration divided by the uncorrected
grations (typically three) are required for each measurement. A
internal standard concentration determined by analysis.
typical integration time is 10 s.
8.2 Dissolve the organometallic compound representing the
11. Preparation of Test Specimens
internal standard in dilution solvent and transfer to a dispensing
11.1 Diluent—Diluent refers to the dilution solvent contain-
vessel. The stability of this solution must be monitored and
prepared fresh (typically weekly) when the concentration of the ing the internal standard (refer to 8.2).
11.2 Test specimen solutions are prepared in the same way
internal standard element changes significantly. The concen-
tration of internal standard element shall be at least 100 times that calibration standards are prepared (refer to 12.2). The mass
% oil in diluent must be the same for calibration standards and
its detection limit. A concentration in the range of 10 to 20
mg/kg is typical. test specimen solutions.
11.2.1 Lubricating Oil Specimens—Weigh approximately
NOTE 1—This test method specifies that the internal standard is
0.5 g oil to the nearest 0.001 g and dilute by mass with the
combined with the dilution solvent because this technique is common and
diluent. Mix well.
efficient when preparing many samples. However, the internal standard
11.2.2 Additive Packages—The concentrations of additive
can be added separately from the dilution solvent as long as the internal
standard concentration is constant or accurately known. elements in additive packages are typically ten times the
concentrations in lubricating oils. Therefore, add
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