ASTM D6481-99(2010)
(Test Method)Standard Test Method for Determination of Phosphorus, Sulfur, Calcium, and Zinc in Lubrication Oils by Energy Dispersive X-ray Fluorescence Spectroscopy
Standard Test Method for Determination of Phosphorus, Sulfur, Calcium, and Zinc in Lubrication Oils by Energy Dispersive X-ray Fluorescence Spectroscopy
SIGNIFICANCE AND USE
Some oils are formulated with organo-metallic additives, which act, for example, as detergents, antioxidants, and antiwear agents. Some of these additives contain one or more of these elements: calcium, phosphorus, sulfur, and zinc. This test method provides a means of determining the concentrations of these elements, which in turn provides an indication of the additive content of these oils.
This test method is primarily intended to be used at a manufacturing location for monitoring of additive elements in lubricating oils. It can also be used in central and research laboratories.
SCOPE
1.1 This test method covers the quantitative determination of additive elements in unused lubricating oils, as shown in Table 1.
1.2 This test method is limited to the use of energy dispersive X-ray fluorescence (EDXRF) spectrometers employing an X-ray tube for excitation in conjunction with the ability to separate the signals of adjacent elements.
1.3 This test method uses interelement correction factors calculated from empirical calibration data.
1.4 This test method is not suitable for the determination of magnesium and copper at the concentrations present in lubricating oils.
1.5 This test method excludes lubricating oils that contain chlorine or barium as an additive element.
1.6 This test method can be used by persons who are not skilled in X-ray spectrometry. It is intended to be used as a routine test method for production control analysis.
1.7 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 to use.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6481 − 99(Reapproved 2010)
Standard Test Method for
Determination of Phosphorus, Sulfur, Calcium, and Zinc in
Lubrication Oils by Energy Dispersive X-ray Fluorescence
Spectroscopy
This standard is issued under the fixed designation D6481; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope simultaneous measurements employing primary and secondary
beam filters. There can be correction of measured intensities
1.1 This test method covers the quantitative determination
for spectral overlap. Concentrations of the elements of interest
of additive elements in unused lubricating oils, as shown in
are determined by comparison of these intensities against a
Table 1.
calibration curve using empirical interelement correction fac-
1.2 This test method is limited to the use of energy
tors and ratio to backscatter.
dispersive X-ray fluorescence (EDXRF) spectrometers em-
2.2 The EDXRF spectrometer is initially calibrated using a
ploying an X-ray tube for excitation in conjunction with the
ability to separate the signals of adjacent elements. setofpreparedstandardstocollectthenecessaryintensitydata.
Each calibration line and any correction coefficient are ob-
1.3 This test method uses interelement correction factors
tained by a regression of this data, using the program supplied
calculated from empirical calibration data.
with the spectrometer.
1.4 This test method is not suitable for the determination of
magnesium and copper at the concentrations present in lubri-
3. Significance and Use
cating oils.
3.1 Some oils are formulated with organo-metallic
1.5 This test method excludes lubricating oils that contain
additives, which act, for example, as detergents, antioxidants,
chlorine or barium as an additive element.
and antiwear agents. Some of these additives contain one or
1.6 This test method can be used by persons who are not
more of these elements: calcium, phosphorus, sulfur, and zinc.
skilled in X-ray spectrometry. It is intended to be used as a
This test method provides a means of determining the concen-
routine test method for production control analysis.
trations of these elements, which in turn provides an indication
1.7 This standard does not purport to address all of the of the additive content of these oils.
safety concerns, if any, associated with its use. It is the
3.2 This test method is primarily intended to be used at a
responsibility of the user of this standard to establish appro-
manufacturing location for monitoring of additive elements in
priate safety and health practices and determine the applica-
lubricating oils. It can also be used in central and research
bility of regulatory limitations to use.
laboratories.
2. Summary of Test Method
4. Interferences
2.1 A specimen is placed in the X-ray beam, and the
4.1 The additive elements found in lubricating oils will
appropriate regions of its spectrum are measured to give the
affect the measured intensities from the elements of interest to
fluorescent intensities of phosphorus, sulfur, calcium, and zinc.
a varying degree. In general, for lubricating oils, the
Other regions of the spectrum are measured to compensate for
X-radiation emitted by the element of interest can be absorbed
varying background. If the detector does not completely
by itself (self-absorption) or by the other elements present in
resolve all the elements in a single measurement, then to
the sample matrix. Also the X-radiation emitted from one
improve selectivity, there is a combination of sequential and
element can further excite (enhance) another element. These
interelement effects are significant at concentrations varying
from 0.03 mass %, due to the heavier elements, to 1 mass %,
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
forthelighterelements.Enhancementeffectscanbeminimised
D02.03 on Elemental Analysis.
byselectiveexcitation.Themeasuredconcentrationforagiven
Current edition approved May 1, 2010. Published May 2010. Originally
element can be mathematically corrected for self-absorption
approved in 1999. Last previous edition approved in 2004 as D6481 - 99 (2004).
DOI: 10.1520/D6481-99R10. and for interelement effects by other elements present in the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6481 − 99 (2010)
TABLE 1 Elements and Range of Concentrations Determined
5.4 Drift Correction Monitors, to correct for instrumental
Element Concentration Range drift. At least two samples are necessary to correct both
Phosphorus 0.02 to 0.3 mass % sensitivity and baseline drifts. For each element and scatter
Sulfur 0.05 to 1.0 mass %
region, there shall be one providing a count rate similar to
Calcium 0.02 to 1.0 mass %
samples from the upper end of the calibration and another
Zinc 0.01 to 0.3 mass %
providing a count rate as if from a blank. This last can be a
blank oil. For the high concentration of each element, a glass
disk, XRF fusion bead, or pressed pellet have all been found to
be satisfactory. They can be the same samples as in 5.3.
sample matrix. If an element is present at significant concen-
trations and an inter-element correction for that element is not
6. Reagents and Materials
employed, the results can be low due to absorption or high due
6.1 Reagent grade chemicals shall be used in all tests.
to enhancement.
Unless otherwise indicated, it is intended that all reagents
4.2 If a sample containing barium as an additive above 0.03 conform to the specifications of the Committee on Analytical
mass % is measured against a calibration derived from stan- Reagents of the American Chemical Society where such
dards without barium, then results will be low. specifications are available. Other grades can be used, pro-
vided it is first ascertained that the reagent is of sufficiently
4.3 If a sample containing chlorine as an impurity above
high purity to permit its use without lessening the accuracy of
0.03 mass % is measured against a calibration derived from
the determination.
standards without chlorine, then the results can be affected.
6.2 Helium, at least 99.5 % purity, for the optical path of the
4.4 There can be spectral overlap of one element onto
spectrometer.
another, especially for phosphorus on sulfur, and the instru-
6.3 Diluent Solvent, a suitable solvent free of metals,
mentmustincludecorrectionproceduresforanysuchoverlaps.
phosphorus, and chlorine, and containing less than 10 ppm of
5. Apparatus
sulfur (for example, deodorized kerosene, white oil, or mineral
oil).
5.1 Energy Dispersive X-ray Fluorescent Analyzer—Any
energy dispersive X-ray fluorescent analyzer can be used if its
6.4 Calibration Standard Materials:
design incorporates at least the following features. 6.4.1 Certified concentration solutions, of liquid organo-
5.1.1 Source of X-ray Excitation , X-ray tube with palla-
metallic salts, each containing calcium or zinc, or both. The
dium,silver,orrhodiumtargetprogrammablebetween4andat solutions shall be sulfur free or the certificate shall state the
least 25 keV for preferential excitation to simplify the sample
concentration of sulfur. Alternatively, the following standard
spectra. (Warning—Operation of an analyzer using an X-ray materials can be used.
tube source is to be conducted in accordance with the manu-
6.4.1.1 Calcium 2-Ethylhexanoate, approximately 12.3
facturer’s safety instructions and federal, state, and local mass % calcium, with a certified value.
regulations)
6.4.1.2 Zinc Cyclohexanebutyrate,approximately16.2mass
5.1.2 X-ray Detector, gas filled proportional counter with % zinc, with a certified value.
high sensitivity and a resolution value not to exceed 1300 eV
6.4.2 Bis(2-Ethylhexyl)Hydrogen Phosphate, 97 % purity
at 5.9 keV. (9.62 mass % phosphorus).
6.4.3 Di-n-butyl Sulfide, 97 % purity, (21.9 mass % sulfur).
NOTE1—Thelimiteddatafrominstrumentswithsolidstatedetectorsin
6.4.4 Stabilizers, 2-ethylhexanoic acid, 2-ethylamine. Also,
the inter-laboratory precision study did not support their inclusion in the
method. proprietarystabilizer/chelatingsolutionsareavailablecommer-
cially. Stabilizers shall be free of the additive element.
5.1.3 Primary Beam Filters, to make the excitation more
selective.
NOTE 2—In addition to the calibration standard materials identified in
5.1.4 Secondary Beam Filters—When a proportional coun- 6.4.1-6.4.3, single or multielement calibration standards can also be
prepared from materials similar to the samples being analyzed, provided
ter is used, these are necessary as a means of discriminating
the calibration standards to be used have previously been characterized by
between an analyte’s X rays and other analytes and the
independent primary (for example, gravimetric or volumetric) analytical
spectrum from the X-ray tube.
techniques to establish the elemental concentration mass % levels.
5.1.5 Multi-Channel Analyzer, for discrimination between
7. Preparation of Calibration Standards
an analyte’s X rays and background X rays.
5.1.6 Optional Helium Purgeable Optical Path. 7.1 To ensure complete solution of all components, prepare
calibration standards by precisely weighing the organo-
5.2 Sample Cells, providing a depth of at least 6 mm and
metallic solutions and phosphorus and sulfur solutions with the
equipped with replaceable X-ray transparent film. Suitable
films include polypropylene and polycarbonate with thickness
Reagent Chemicals, American Chemical Society Specifications, American
from 3.5 to 8 µm.
Chemical Society, Washington, D.C. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
5.3 Instrument Setting-Up Sam
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