ASTM D7214-07a(2012)
(Test Method)Standard Test Method for Determination of the Oxidation of Used Lubricants by FT-IR Using Peak Area Increase Calculation
Standard Test Method for Determination of the Oxidation of Used Lubricants by FT-IR Using Peak Area Increase Calculation
SIGNIFICANCE AND USE
5.1 The PAI is representative of the quantity of all the compounds containing a carbonyl function that have formed by the oxidation of the lubricant (aldehydes, ketones, carboxylic acids, esters, anhydrides, etc.). The PAI gives representative information on the chemical degradation of the lubricant which has been caused by oxidation.
5.2 This test method was developed for transmission oils and is used in the CEC L-48-A-00 test (Oxidation Stability of Lubricating Oils Used in Automotive Transmissions by Artificial Aging) as a parameter for the end of test evaluation.
SCOPE
1.1 This test method covers the determination of the oxidation of used lubricants by FT-IR (Fourier Transform Infrared Spectroscopy). It measures the concentration change of constituents containing a carbonyl function that have formed during the oxidation of the lubricant.
1.2 This test method may be used to indicate relative changes that occur in an oil under oxidizing conditions. The test method is not intended to measure an absolute oxidation property that can be used to predict performance of an oil in service.
1.3 This test method was developed for transmission oils which have been degraded either in service, or in a laboratory test, for example a bulk oxidation test. It may be used for other in-service oils, but the stated precision may not apply.
1.4 The results of this test method may be affected by the presence of other components with an absorbance band in the zone of 1600–1800 cm-1. Low PAI values may be difficult to determine in those cases. Section 6 describes these possible interferences in more detail.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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: D7214 − 07a (Reapproved 2012)
Standard Test Method for
Determination of the Oxidation of Used Lubricants by FT-IR
Using Peak Area Increase Calculation
This standard is issued under the fixed designation D7214; 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.
INTRODUCTION
This test method was jointly developed with “Groupement Francais de Coordination” (GFC),
technicalcommitteeLM5and“CoordinatingEuropeanCouncil”(CEC) SurveillanceGroupT-048for
the purpose of monitoring the oxidation stability of artificially aged automotive transmission fluids.
This test method has been used in the CEC L-48-A-00 method as an end of test measurement
parameter.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method covers the determination of the oxida-
bility of regulatory limitations prior to use.
tion of used lubricants by FT-IR (Fourier Transform Infrared
Spectroscopy). It measures the concentration change of con-
2. Referenced Documents
stituents containing a carbonyl function that have formed
2.1 ASTM Standards:
during the oxidation of the lubricant.
D4057 Practice for Manual Sampling of Petroleum and
1.2 This test method may be used to indicate relative
Petroleum Products
changes that occur in an oil under oxidizing conditions. The
D4177 Practice for Automatic Sampling of Petroleum and
test method is not intended to measure an absolute oxidation
Petroleum Products
property that can be used to predict performance of an oil in
D6299 Practice for Applying Statistical Quality Assurance
service.
and Control Charting Techniques to Evaluate Analytical
1.3 This test method was developed for transmission oils
Measurement System Performance
which have been degraded either in service, or in a laboratory
E131 Terminology Relating to Molecular Spectroscopy
test, for example a bulk oxidation test. It may be used for other
E1421 Practice for Describing and Measuring Performance
in-service oils, but the stated precision may not apply.
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
eters: Level Zero and Level One Tests
1.4 The results of this test method may be affected by the
E1866 Guide for Establishing Spectrophotometer Perfor-
presence of other components with an absorbance band in the
-1
mance Tests
zone of 1600–1800 cm . Low PAI values may be difficult to
determine in those cases. Section 6 describes these possible
2.2 CEC Standard:
interferences in more detail.
CEC L-48-A-00 Oxidation Stability of Lubricating Oils
Used in Automotive Transmissions by Artificial Aging
1.5 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3. Terminology
standard.
3.1 Definitions—For terminology relating to molecular
1.6 This standard does not purport to address all of the
spectroscopic methods, refer to Terminology E131.
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D02.96.03 on FTIR Testing Practices and Techniques Related to contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
In-Service Lubricants. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2012. Published November 2012. Originally the ASTM website.
approved in 2006. Last previous edition approved in 2007 as D7214–07a. DOI: Available from Coordinating European Council (CEC), c/o Interlynk Admin-
10.1520/D7214-07AR12. istrative Services, Ltd., P.O. Box 6475, Earl Shilton, Leicester, LE9 9ZB, U.K.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7214 − 07a (2012)
3.2.1 carbonyl region, n—region of the FT-IR spectrum tee onAnalytical Reagents of theAmerican Chemical Society,
corresponding to the absorbance of compounds containing a where such specifications are available. Other grades may be
carbonyl function. Depending on the nature of the carbonyl
used, provided it is first ascertained that the reagent is of
compounds, this region is usually located between approxi- sufficiently high purity to permit its use without lessening the
-1 -1
mately 1820 cm and 1650 cm .
accuracy of the determination.
3.2.2 differential spectrum, n—FT-IR absorbance spectrum
8.2 Heptane, used as cleaning solvent. Other solvents and
resulting from the subtraction of the fresh oil from the used oil.
solvent mixtures may be used provided they adequately clean
3.2.3 PAI (peak area increase), n—area of the carbonyl
the cell(s) between samples. A 50/50 mixture of cyclohexane
region of the differential FT-IR spectrum, divided by the cell
and toluene has been found to be useful in cleaning cells after
pathlength in millimetres. In this standard, PAI refers to a
highly contaminated and degraded samples have been run.
relative measurement of the oxidation of a used lubricant by
(Warning—Flammable.)
FT-IR.
8.3 PAO4, used as dilution oil (PAO4: PolyAlphaOlefin
4. Summary of Test Method withakinematicviscosityat100°Cofapproximately4mm /s)
4.1 FT-IR spectra of the fresh oil and of the used oil are
9. Calibration and Standardization
recorded in a transmission cell of known pathlength. Both
spectra are converted to absorbance and then subtracted. Using
9.1 Calculation of the Cell Pathlength—Use a cell with a
this resulting differential spectrum, a baseline is set under the
knownpathlengthofapproximately0.025to0.1mm.Calibrate
-1
peak corresponding to the carbonyl region around 1650 cm
the infrared cell pathlength using the interference fringe
-1
and 1820 cm and the area created by this baseline and the
method:
carbonyl peak is calculated. The area of the carbonyl region is
9.1.1 Acquire the single beam background infrared spec-
divided by the cell pathlength in millimetres and this result is
trum.Usingtheemptyinfraredcellintheinfraredspectrometer
reported as Peak Area Increase (PAI).
sample compartment, acquire the cell single beam infrared
spectrum. Calculate the transmittance spectrum by dividing the
5. Significance and Use
cell single beam spectrum by the background single beam
5.1 The PAI is representative of the quantity of all the
spectrum. Optionally, convert the transmittance spectrum to an
compoundscontainingacarbonylfunctionthathaveformedby
absorbance spectrum by taking the negative logarithm (base
the oxidation of the lubricant (aldehydes, ketones, carboxylic
10) of the transmittance spectrum. The fringe calculation may
acids, esters, anhydrides, etc.). The PAI gives representative
be done on either the transmittance or absorbance. spectrum.
informationonthechemicaldegradationofthelubricantwhich
The final spectrum is obtained by subtraction of the back-
has been caused by oxidation.
ground spectrum from the cell spectrum.
5.2 This test method was developed for transmission oils
NOTE 1—This computation is generally an integral part of the infrared
and is used in the CEC L-48-A-00 test (Oxidation Stability of
spectrometer software.
Lubricating Oils Used in Automotive Transmissions by Artifi-
cial Aging) as a parameter for the end of test evaluation. 9.1.2 Choose 2 minima separated by about 20 measurable
interference fringes as shown in Fig. 1. Count the number of
6. Interferences
interference fringes between the lower and the higher
6.1 Some specific cases (very viscous oil, use of ester as wavenumbers, referred to as λ and λ .
1 2
base stock, high soot content) may require a dilution of the
NOTE 2—The spectral range may be chosen freely in an area where the
sample and a specific area calculation, which are described in
fringes are regular.
14.1 – 14.3. In those cases, the result is corrected by a dilution
9.1.3 The cell pathlength is calculated by the formula:
factor, which is applied to the sample.
5·n
7. Apparatus
e 5 (1)
λ 2 λ
~ !
1 2
7.1 FT-IR Spectrophotometer, suitable for recording mea-
-1 -1
where:
surements between 1650 cm and 1820 cm and with a
-1
e = the pathlength in mm, and
resolution of 4 cm .
n = the number of fringes between λ and λ .
1 2
7.2 Transmission Cell,withwindowsofpotassiumbromide,
having a known pathlength of approximately 0.025 to 0.1 mm. 9.2 Instrument Performance Checks:
9.2.1 Periodically, the performance of the FT-IR instrument
7.3 Syringe, or Other Automated or Semi-Automated
should be monitored using the Level 0 procedure of Practice
Device, with adequate volume to fill the cell, for example, 2
E1421. If significant change in performance is noted, then
mL.
testing should be suspended until the cause of the performance
8. Reagents and Materials
change is diagnosed and corrected.
8.1 Purity of Reagents—Reagent grade chemicals shall be 9.2.2 Alternative instrument performance tests conforming
used in all tests. Unless otherwise indicated, it is intended that totherecommendationsofGuideE1866maybesubstitutedfor
all reagents shall conform to the specifications of the commit- the Practice E1421 test.
D7214 − 07a (2012)
FIG. 1 Example of Interference Fringes for Cell Pathlength Calculation
10. Conditioning 12. Procedure
10.1 Before using the infrared cell ensure that it is clean by 12.1 Acquire a single beam background spectrum. This
washing through with a suitable solvent, for example, heptane. background spectrum may be used in the conversion of all
Dry the cell using dry air or nitrogen, if necessary. Calibrate subsequent spectra for at least one day.
this cell as described in Section 9.
12.2 With a syringe or other injection device, fill the cell
with the fresh oil, and record its single beam sample spectrum.
11. Preparation of Sample of Used Oil
Convert this spectrum to a transmittance spectrum by dividing
11.1 Refer to Practice D4057 (Manual Sampling) or Prac- it by the single beam background spectrum and to a fresh oil
tice D4177 (Automatic Sampling) for proper sampling tech- absorbance spectrum by taking the negative logarithm (base
10) of the transmittance spectrum. Accumulate an adequate
niques.
number of scans for a satisfactory noise level of < 2 mAbs
11.2 When sampling used lubricants, the specimen shall be
-1
@2000 cm .
representative of the system sampled and shall be free of
contamination from external sources. As used oil can change
NOTE 3—Assuming there are no absorbance peaks in the range from
-1
2050 to 1950 cm for the sample, the noise level may be estimated as the
appreciably in storage, test samples as soon as possible after
standard deviation of the absorbance data over this spectral range.
removal from the lubricating system and note the dates of
sampling and testing.
12.3 Empty and clean the cell. Heptane may be used. Fill
the cell with the aged oil, and record its single beam sample
11.3 Ifthesampleofusedoilcontainsvisiblesediment,heat
spectrum. Convert this spectrum to a transmittance spectrum
to 60 6 5°C in the original container and agitate until all of the
bydividingbythesinglebeambackgroundspectrum,andtoan
sedimentishomogeneouslysuspendedintheoil.Iftheoriginal
aged oil absorbance spectrum by taking the negative logarithm
container is a can or if it is glass and more than three-fourths
(base 10) of the transmittance spectrum.
full, transfer the entire sample to a clear-glass bottle having a
NOTE 4—It may happen that the aged oil is too viscous to fill the cell.
capacity at least one third greater than the volume of the
Then it is possible to proceed to a dilution as described in 12.4.1.
sample. Transfer all traces of sediment from the original
container to the bottle by vigorous agitation of portions of the 12.4 Generate a differential spectrum by subtracting the
sample in the original container. fresh oil absorbance spectrum from the aged oil absorbance
D7214 − 07a (2012)
spectrum (see Fig. 2). Locate and zoom on the carbonyl region 14. Procedures for Interferences
-1
centered at 1720 cm . Processing may continue if the maxi-
14.1 The results of this test method may be affected by the
mum absorbance of this carbonyl region is lower than 1.5.
presence of other components with an absorbance band in the
-1
zone of 1600–1800 cm . Low PAI values may be difficult to
NOTE 5—Since the carbonyl region absorption minima (close to 1820
-1
-1
cm and 1650 cm ) can vary with the type of oil sample being tested, it
determine in those cases. The following procedures may be
was decided not to use fixed baseline limits for calculating the area A.
used if interferences are present.
NOTE 6—The carbonyl band may consist of more than one peak
14.2 Soot-Containing Oils—The presence of soot degrades
maxima.
NOTE 7—Do not calculate the differential peak area by difference of the the spectra by decreasing the transmittance level. This case
peak area of the aged oil with the peak area of the fresh oil.
mayrequireadilutionasdescribedin12.4inordertoobtainan
absorbance lower than 1.5.
12.4.1 Ifthemaximumabsorbanceofthecarbonylregionof
the differential spectrum is higher than 1.5: dilute with 1 %
14.3 Ester-Containing Oils—The ester functions contained
accuracy by weight both fresh and aged oils with the same
in some lubricants, especially those formulated with ester base
dilution factor, D (PAO 4 is recommended as dilution oil). For
oil, interfere with the oxidation peak. Dilution may be needed
example,D=2fora50% (1:1) wt/wt dilution. Record the two
with these types of lubricants and it is recommended to use a
spectra, convert them to absorbance and subtract them. If the
cell with a small pathlength (0.05 mm maximum). Check the
maximumabsorbanceofthecarbonylregionisstillhigherthan
shape of the spectrum before interpreting it. The residual
-1
1.5, then use a higher dilution factor. This occurrence could
positive or negative peaks at 1740 cm showing the presence
happen in the case of ester or soot-containing oils.
of ester function may make it difficult to correctly perform the
subtraction operation between the aged oil spectrum and the
NOTE 8—The cell pathlength may be changed to 0.05 mm or 0.025 mm
fresh oil spectrum. The different examples below show the
if absorbance in the assessment area is greater than 1.5.
NOTE 9—Dilution factors are commonly chosen between 2 and 10.
different cases that c
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