ASTM D7751-11
(Test Method)Standard Test Method for Determination of Additive Elements in Lubricating Oils by EDXRF Analysis
Standard Test Method for Determination of Additive Elements in Lubricating Oils by EDXRF Analysis
SIGNIFICANCE AND USE
Lubricating oils are formulated with organo-metallic additives, which act, for example, as detergents, antioxidants, antifoaming, or antiwear agents, or a combination thereof. Some of these additives contain one or more of the following elements: magnesium, phosphorus, sulfur, chlorine, calcium, zinc, and molybdenum. 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.
Additive packages are the concentrates that are used to blend lubricating oils.
This test method is primarily intended to be used for the monitoring of additive elements in lubricating oils.
If this test method is applied to lubricating oils with matrices significantly different from the calibration materials specified in this test method, the cautions and recommendations in Section 6 should be observed when interpreting the results.
SCOPE
1.1 This test method covers the quantitative determination of additive elements in unused lubricating oils and additive packages, as shown in Table 1. The pooled limit of quantitation of this test method as obtained by statistical analysis of interlaboratory test results is 0.02% for magnesium, 0.003 % for phosphorus, 0.002 % for sulfur, 0.001 % for chlorine, 0.003 % for calcium, 0.001 % for zinc, and 0.002 % for molybdenum.
1.2 Additive packages require dilution with a contamination free diluent (base oil) prior to analysis. The dilution factor has to be calculated from the expected concentrations to bring the concentrations for all elements into the ranges listed in Table 1.
1.3 Some lubrication oils will contain higher concentrations than the maximum concentrations listed in Table 1. These samples require dilution with a contamination free diluent (base oil) prior to analysis. The dilution factor has to be calculated from the expected concentrations to bring the concentrations for all elements into the ranges listed in Table 1.
1.4 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 by using a high resolution semiconductor detector.
1.5 This test method uses inter-element correction factors calculated from a fundamental parameters (FP) approach or from another matrix correction method.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6.1 The preferred concentration units are mg/kg or mass %.
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 prior to use.
TABLE 1 Elements and Range of Applicability
General Information
Relations
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:D7751–11
Standard Test Method for
Determination of Additive Elements in Lubricating Oils by
EDXRF Analysis
This standard is issued under the fixed designation D7751; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the quantitative determination
of additive elements in unused lubricating oils and additive D4057 Practice for Manual Sampling of Petroleum and
packages,asshowninTable1.Thepooledlimitofquantitation Petroleum Products
of this test method as obtained by statistical analysis of D4177 Practice for Automatic Sampling of Petroleum and
interlaboratory test results is 0.02% for magnesium, 0.003 % Petroleum Products
forphosphorus,0.002%forsulfur,0.001%forchlorine,0.003 D6299 Practice for Applying Statistical Quality Assurance
% for calcium, 0.001 % for zinc, and 0.002 % for molybde- and Control Charting Techniques to Evaluate Analytical
num. Measurement System Performance
1.2 Additivepackagesrequiredilutionwithacontamination D6300 Practice for Determination of Precision and Bias
free diluent (base oil) prior to analysis. The dilution factor has Data for Use in Test Methods for Petroleum Products and
to be calculated from the expected concentrations to bring the Lubricants
concentrationsforallelementsintotherangeslistedinTable1. D6792 Practice for Quality System in Petroleum Products
1.3 Some lubrication oils will contain higher concentrations and Lubricants Testing Laboratories
than the maximum concentrations listed in Table 1. These D7343 Practice for Optimization, Sample Handling, Cali-
samples require dilution with a contamination free diluent bration, and Validation of X-ray Fluorescence Spectrom-
(base oil) prior to analysis. The dilution factor has to be etry Methods for Elemental Analysis of Petroleum Prod-
calculated from the expected concentrations to bring the ucts and Lubricants
concentrationsforallelementsintotherangeslistedinTable1. E1621 Guide for X-Ray Emission Spectrometric Analysis
1.4 This test method is limited to the use of energy 2.2 ISO Standards:
dispersive X-ray fluorescence (EDXRF) spectrometers em- ISO 4259 Determination and application of precision data
ploying an X-ray tube for excitation in conjunction with the in relation to methods of test
ability to separate the signals of adjacent elements by using a
3. Terminology
high resolution semiconductor detector.
1.5 This test method uses inter-element correction factors 3.1 Definitions:
3.1.1 energy dispersive X-ray spectrometry, n—XRF spec-
calculated from a fundamental parameters (FP) approach or
from another matrix correction method. trometry applying energy dispersive selection of radiation.
3.2 Abbreviations:
1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 3.2.1 EDXRF—Energy Dispersive X-ray Fluorescence
Spectrometry.
standard.
1.6.1 The preferred concentration units are mg/kg or mass 3.2.2 FP—Fundamental Parameters.
%.
4. Summary of Test Method
1.7 This standard does not purport to address all of the
4.1 A specimen is placed in the X-ray beam, and the
safety concerns, if any, associated with its use. It is the
appropriate regions of its spectrum are measured to give the
responsibility of the user of this standard to establish appro-
fluorescent intensities of magnesium, phosphorus, sulfur, chlo-
priate safety and health practices and determine the applica-
rine, calcium, zinc, and molybdenum. Other regions of the
bility of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee D02 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee Standards volume information, refer to the standard’s Document Summary page on
D02.03 on Elemental Analysis. the ASTM website.
CurrenteditionapprovedOct.1,2011.PublishedNovember2011.DOI:10.1520/ Available from International Organization for Standardization (ISO), 1, ch. de
D7751-11. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7751–11
TABLE 1 Elements and Range of Applicability
5.4 If this test method is applied to lubricating oils with
Element Concentration Range in mass % matrices significantly different from the calibration materials
specified in this test method, the cautions and recommenda-
Magnesium 0.02 to 0.4
Phosphorous 0.003 to 0.25
tions in Section 6 should be observed when interpreting the
Sulfur 0.002 to 1.5
results.
Chlorine 0.001 to 0.4
Calcium 0.003 to 1.0
Zinc 0.001 to 0.25
6. Interferences
Molybdenum 0.002 to 0.05
6.1 The additive elements found in lubricating oils will
affect the measured intensities from the elements of interest to
a varying degree. In general the X-radiation emitted by the
spectrum are measured to compensate for matrix variation. To
element of interest can be absorbed by itself (self-absorption)
optimize the sensitivity for each element or group of elements,
or by the other elements present in the sample matrix.Also the
a combination of optimized excitation and detection conditions
X-radiation emitted from one element can further excite
may be used (no more than two conditions should be used in
(enhance) another element. These inter-element effects are
order to keep the analysis time as short as possible, typically
significant at concentrations varying from 0.03 mass %, due to
under ten minutes). There may be a correction of measured
the higher atomic number elements (for example, molybde-
intensities for spectral overlap.
num), to 1 mass %, for the lower atomic number elements (for
4.1.1 Concentrations of the elements of interest are deter-
example, sulfur). If an element is present at significant con-
mined by comparison of these intensities against a calibration
centrations and an inter-element correction for that element is
curve using a fundamental parameters (FP) approach, possibly
not employed, the results can be low due to absorption or high
combined with corrections from backscatter. The FP approach
due to enhancement.
uses the physical processes forming the basis of X-ray fluo-
6.2 Absorption and enhancements effects will be corrected
rescence emission in order to provide a theoretical model for
by corrections from the FP approach or by other matrix
the correction of matrix effects. The correction term is calcu-
correction models.
lated from first principle expressions derived from basic
6.3 There can be spectral overlap of one element onto
physical principles and contain physical constants and param-
another, and the instrument must include correction procedures
eters that include absorption coefficients, fluorescence yield,
for any such overlaps.
primary spectral distribution and spectrometry geometry. The
calculation of concentrations in samples is based on making
7. Apparatus
successively better estimates of composition by an iteration
7.1 Energy Dispersive X-ray Fluorescent Spectrometer—
procedure.
Any energy dispersive X-ray fluorescence spectrometer can be
NOTE 1—The algorithm used for the procedure is usually implemented
used if its design incorporates at least the following features:
in the instrument manufacturer’s software.
7.1.1 Source of X-ray Excitation—X-ray tube with palla-
4.2 The EDXRF spectrometer is initially calibrated using a dium, silver, rhodium, or tungsten target. Other targets may be
suitable as well. The voltage of the X-ray tube shall be
set of standards to collect the necessary intensity data. Each
calibration line and any correction coefficient are obtained by a programmable between 4 and at least 30 kV for preferential
excitation of elements or groups of elements.
regression of this data, using the program supplied with the
spectrometer. (Warning—Exposure to excessive quantities of 7.1.2 X-ray Detector—Semiconductor detector with high
X-radiation is injurious to health. The operator needs to take
sensitivityandaspectralresolutionvaluenottoexceed175eV
appropriate actions to avoid exposing any part of their body, at 5.9 keV.
not only to primary X-rays, but also to secondary or scattered
7.1.3 Primary Beam Filters (Optional)—To make the exci-
radiation that might be present.The X-ray spectrometer should tation more selective and to reduce the intensity of background
be operated in accordance with the regulations governing the
radiation.
use of ionizing radiation.) 7.1.4 Secondary or Polarization Targets, or Both
(Optional)—To make the excitation more selective and to
5. Significance and Use
improve peak-to-background ratio.
7.1.5 SignalConditioningandDataHandlingElectronics—
5.1 Lubricating oils are formulated with organo-metallic
That include the functions of X-ray intensity counting, spectra
additives, which act, for example, as detergents, antioxidants,
handling by background variation correction, overlap correc-
antifoaming, or antiwear agents, or a combination thereof.
tions, inter-elements effects corrections, and conversion of
Some of these additives contain one or more of the following
X-ray intensity into concentration.
elements: magnesium, phosphorus, sulfur, chlorine, calcium,
zinc, and molybdenum. This test method provides a means of 7.1.6 Helium Purgeable Optical Path (Optional)—Helium
purge improves the sensitivity of low energy X-rays emitted
determiningtheconcentrationsoftheseelements,whichinturn
provides an indication of the additive content of these oils. from low atomic number elements (Z< 22).
7.1.7 Sample Cells—Providing a depth of at least 6 mm and
5.2 Additive packages are the concentrates that are used to
blend lubricating oils. equipped with replaceable X-ray transparent film.
5.3 This test method is primarily intended to be used for the 7.1.8 Sample Film—Suitable films include polypropylene,
monitoring of additive elements in lubricating oils. polyester, and polycarbonate with thickness from 3.5 to 8 µm.
D7751–11
Athickfilmmaylimittheperformanceforlowatomicnumbers 8.4.2.3 Bis(2-Ethylhexyl)Hydrogen Phosphate, 97 % purity
(for example, Magnesium). (approximately 9.62 mass % phosphorus).
7.2 Instrument Setting-Up Samples (Elemental Reference
8.4.2.4 Di-n-butyl Sulfide, 97 % purity (approximately 21.9
Samples) (Optional)—To quantify spectral overlaps. These are mass % sulfur).
not required when the instrument’s software does include
8.4.2.5 Magnesium-2-ethylhexoate, (2.99 % magnesium).
software to deconvolute spectra.
8.4.2.6 1-Chlorooctane, 98 % purity, (23.9 mass % chlo-
7.3 Drift Correction Monitors (Optional)—To correct for
rine).
instrumentaldrift.Atleasttwosamplesarenecessarytocorrect
8.4.2.7 Commercially available single element standard for
both sensitivity and possible changes in the background. For
molybdenum based on molybdenumsulfonate.
each element and scatter region, there shall be one providing a
8.4.2.8 Stabilizers, 2-ethylhexanoic acid, 2-ethylamine, also
count rate similar to samples from the upper end of the
proprietarystabilizer/chelatingsolutionsareavailablecommer-
calibration and another providing a count rate as if from a
cially. Stabilizers shall be free of the additive element.
blank. This last can be a blank oil. For the high concentration
NOTE 3—In addition to the calibration standard materials identified in
of each element, a glass disk, XRF fusion bead, or pressed
8.4,singleormultielementcalibrationstandardscanalsobepreparedfrom
pellet have all been found to be satisfactory. Elemental
materials similar to the samples being analyzed, provided the calibration
reference samples (7.2) may also be used.
standards to be used have previously been characterized by independent
7.3.1 Drift correction is usually implemented automatically
primary (for example, gravimetric or volumetric) analytical techniques to
in software, although the calculation can readily be done
establish the elemental concentration mass % levels.
manually. For X-ray instruments that are highly stable, the
magnitude of the drift correction factor may not differ signifi- 9. Hazards
cantly from unity.
9.1 Occupational health and safety standards for X-rays and
7.4 Quality Control (QC) Samples (Optional)—Samples for
ionizing radiation shall be observed. It is also recommended
useinestablishingandmonitoringthestabilityandprecisionof
that proper practices be followed as presented by most manu-
an analytical measurement system. Use homogeneous materi-
factures documentation or described in Guide E1621.
als, similar to samples of interest and available in sufficient
quantity to be analyzed regularly for a long period of time.
10. Sampling and Test Specs and Units
7.5 Foradditionalinformation,alsorefertoPracticeD7343.
10.1 Samples shall be taken in accordance with the instruc-
NOTE 2—Verification of system control through the use of QC samples
tions in Practices D4057 or D4177. For sample handling, also
and control charting is highly recommended.
refer to Practice D7343.
10.2 When reusable sample cells are used, clean and dry
8. Reagents and Materials
cells before each use. Disposable sample cells shall not be
8.1 Purity of Reagents —Reagent grade chemicals shall be
reused. For each sample, an unused piece of X-ray film is
used in all tests. Unless otherwise indicated, it is intended that
required for the sample cell. Avoid touching the inside of the
all reagents conform to the specifications of the Committee on
sample cell, the portion of the window film in the cell, or the
Analytical Reagents of the American Chemical Society where
instrument window that is exposed to X-rays. Oil from
such specifications are available. Other grades may be used,
fingerprintscanaffectthereadingwhendetermininglowlevels
provided it is first ascertained that the reagent is of sufficiently
of analytes. Wrinkles in the film will affect the intensity of the
high purity to permit its use without lessening the accuracy of
X-raystransmitted,therefore,itisessentialthatthefilmbetaut
the determination.
andcleantoensurereliableresults.Whenhandlingthewindow
8.2 Diluent Solvent—Asuitablesolventcontaininglessthan
film, avoid touching the central part (the part that actually
10 mg/kg of sulfur and containing less than 1 mg/kg of metals
forms the optical window) as this can lead to contamination
as well as of all other ele
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