ASTM D7214-07a(2019)
(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 cm-1 to 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: D7214 − 07a (Reapproved 2019)
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, health, and environmental practices and deter-
1.1 This test method covers the determination of the oxida-
mine the applicability of regulatory limitations prior to use.
tion of used lubricants by FT-IR (Fourier Transform Infrared
1.7 This international standard was developed in accor-
Spectroscopy). It measures the concentration change of con-
dance with internationally recognized principles on standard-
stituents containing a carbonyl function that have formed
ization established in the Decision on Principles for the
during the oxidation of the lubricant.
Development of International Standards, Guides and Recom-
1.2 This test method may be used to indicate relative
mendations issued by the World Trade Organization Technical
changes that occur in an oil under oxidizing conditions. The
Barriers to Trade (TBT) Committee.
test method is not intended to measure an absolute oxidation
property that can be used to predict performance of an oil in
2. Referenced Documents
service.
2.1 ASTM Standards:
1.3 This test method was developed for transmission oils
D4057 Practice for Manual Sampling of Petroleum and
which have been degraded either in service, or in a laboratory
Petroleum Products
test, for example a bulk oxidation test. It may be used for other
D4177 Practice for Automatic Sampling of Petroleum and
in-service oils, but the stated precision may not apply.
Petroleum Products
D6299 Practice for Applying Statistical Quality Assurance
1.4 The results of this test method may be affected by the
and Control Charting Techniques to Evaluate Analytical
presence of other components with an absorbance band in the
-1 -1
Measurement System Performance
zone of 1600 cm to 1800 cm . Low PAI values may be
E131 Terminology Relating to Molecular Spectroscopy
difficult to determine in those cases. Section 6 describes these
E1421 Practice for Describing and Measuring Performance
possible interferences in more detail.
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
1.5 The values stated in SI units are to be regarded as
eters: Level Zero and Level One Tests
standard. No other units of measurement are included in this
E1866 Guide for Establishing Spectrophotometer Perfor-
standard.
mance Tests
1.6 This standard does not purport to address all of the
2.2 CEC Standard:
safety concerns, if any, associated with its use. It is the
CEC L-48-A-00 Oxidation Stability of Lubricating Oils
Used in Automotive Transmissions by Artificial Aging
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 Dec. 1, 2019. Published December 2019. Originally the ASTM website.
approved in 2006. Last previous edition approved in 2012 as D7214–07a (2012). Available from Coordinating European Council (CEC), c/o Interlynk Admin-
DOI: 10.1520/D7214-07AR19. 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 (2019)
3. Terminology 8. Reagents and Materials
3.1 Definitions—For terminology relating to molecular 8.1 Purity of Reagents—Reagent grade chemicals shall be
spectroscopic methods, refer to Terminology E131. used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the commit-
3.2 Definitions of Terms Specific to This Standard:
tee onAnalytical Reagents of theAmerican Chemical Society,
3.2.1 carbonyl region, n—region of the FT-IR spectrum
where such specifications are available. Other grades may be
corresponding to the absorbance of compounds containing a
used, provided it is first ascertained that the reagent is of
carbonyl function. Depending on the nature of the carbonyl
sufficiently high purity to permit its use without lessening the
compounds, this region is usually located between approxi-
-1 -1 accuracy of the determination.
mately 1820 cm and 1650 cm .
8.2 Heptane, used as cleaning solvent. Other solvents and
3.2.2 differential spectrum, n—FT-IR absorbance spectrum
solvent mixtures may be used provided they adequately clean
resulting from the subtraction of the fresh oil from the used oil.
the cell(s) between samples. A 50/50 mixture of cyclohexane
3.2.3 PAI (peak area increase), n—area of the carbonyl
and toluene has been found to be useful in cleaning cells after
region of the differential FT-IR spectrum, divided by the cell
highly contaminated and degraded samples have been run.
pathlength in millimetres. In this standard, PAI refers to a
(Warning—Flammable.)
relative measurement of the oxidation of a used lubricant by
8.3 PAO4, used as dilution oil (PAO4: PolyAlphaOlefin
FT-IR.
with a kinematic viscosity at 100 °C of approximately
4. Summary of Test Method
4mm /s)
4.1 FT-IR spectra of the fresh oil and of the used oil are
recorded in a transmission cell of known pathlength. Both 9. Calibration and Standardization
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
known pathlength of approximately 0.025 mm to 0.1 mm.
-1
peak corresponding to the carbonyl region around 1650 cm
Calibrate the infrared cell pathlength using the interference
-1
and 1820 cm and the area created by this baseline and the
fringe 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-
9.1.2 Choose 2 minima separated by about 20 measurable
cial Aging) as a parameter for the end of test evaluation.
interference fringes as shown in Fig. 1. Count the number of
6. Interferences
interference fringes between the lower and the higher
wavenumbers, referred to as λ and λ .
1 2
6.1 Some specific cases (very viscous oil, use of ester as
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
e 5 (1)
7. Apparatus
~λ 2 λ !
1 2
7.1 FT-IR Spectrophotometer, suitable for recording mea-
where:
-1 -1
surements between 1650 cm and 1820 cm and with a
e = the pathlength in mm, and
-1
resolution of 4 cm .
n = the number of fringes between λ and λ .
1 2
7.2 Transmission Cell,withwindowsofpotassiumbromide,
9.2 Instrument Performance Checks:
having a known pathlength of approximately 0.025 mm to
9.2.1 Periodically, the performance of the FT-IR instrument
0.1 mm.
should be monitored using the Level 0 procedure of Practice
7.3 Syringe, or Other Automated or Semi-Automated E1421. If significant change in performance is noted, then
Device, with adequate volume to fill the cell, for example, 2 testing should be suspended until the cause of the performance
mL. change is diagnosed and corrected.
D7214 − 07a (2019)
FIG. 1 Example of Interference Fringes for Cell Pathlength Calculation
9.2.2 Alternative instrument performance tests conforming originalcontainertothebottlebyvigorousagitationofportions
totherecommendationsofGuideE1866maybesubstitutedfor of the sample in the original container.
the Practice E1421 test.
12. Procedure
10. Conditioning 12.1 Acquire a single beam background spectrum. This
background spectrum may be used in the conversion of all
10.1 Before using the infrared cell ensure that it is clean by
subsequent spectra for at least one day.
washing through with a suitable solvent, for example, heptane.
12.2 With a syringe or other injection device, fill the cell
Dry the cell using dry air or nitrogen, if necessary. Calibrate
with the fresh oil, and record its single beam sample spectrum.
this cell as described in Section 9.
Convert this spectrum to a transmittance spectrum by dividing
11. Preparation of Sample of Used Oil
it by the single beam background spectrum and to a fresh oil
absorbance spectrum by taking the negative logarithm (base
11.1 Refer to Practice D4057 (Manual Sampling) or Prac-
10) of the transmittance spectrum. Accumulate an adequate
tice D4177 (Automatic Sampling) for proper sampling tech-
number of scans for a satisfactory noise level of < 2 mAbs @
niques.
-1
2000 cm .
11.2 When sampling used lubricants, the specimen shall be
NOTE 3—Assuming there are no absorbance peaks in the range from
representative of the system sampled and shall be free of
-1 -1
2050 cm to 1950 cm for the sample, the noise level may be estimated
contamination from external sources. As used oil can change
as the standard deviation of the absorbance data over this spectral range.
appreciably in storage, test samples as soon as possible after
12.3 Empty and clean the cell. Heptane may be used. Fill
removal from the lubricating system and note the dates of
the cell with the aged oil, and record its single beam sample
sampling and testing.
spectrum. Convert this spectrum to a transmittance spectrum
11.3 Ifthesampleofusedoilcontainsvisiblesediment,heat
bydividingbythesinglebeambackgroundspectrum,andtoan
to60 °C 65 °Cintheoriginalcontainerandagitateuntilallof
aged oil absorbance spectrum by taking the negative logarithm
the sediment is homogeneously suspended in the oil. If the
(base 10) of the transmittance spectrum.
original container is a can or if it is glass and more than NOTE 4—It may happen that the aged oil is too viscous to fill the cell.
Then it is possible to proceed to a dilution as described in 12.4.1.
three-fourths full, transfer the entire sample to a clear-glass
bottle having a capacity at least one third greater than the 12.4 Generate a differential spectrum by subtracting the
volume of the sample. Transfer all traces of sediment from the fresh oil absorbance spectrum from the aged oil absorbance
D7214 − 07a (2019)
spectrum (see Fig. 2). Locate and zoom on the carbonyl region 13.1.1 If no dilution was needed, the dilution factor, D is 1.
-1
centered at 1720 cm . Processing may continue if the maxi-
mum absorbance of this carbonyl region is lower than 1.5.
14. Procedures for Interferences
NOTE 5—Since the carbonyl region absorption minima (close to 14.1 The results of this test method may be affected by the
-1
-1
1820 cm and 1650 cm ) can vary with the type of oil sample being
presence of other components with an absorbance band in the
-1 -1
tested, it was decided not to use fixed baseline limits for calculating the
zone of 1600 cm to 1800 cm . Low PAI values may be
area A.
difficult to determine in those cases. The following procedures
NOTE 6—The carbonyl band may consist of more than one peak
may be used if interferences are present.
maxima.
NOTE 7—Do not calculate the differential peak area by difference of the
14.2 Soot-Containing Oils—The presence of soot degrades
peak area of the aged oil with the peak area of the fresh oil.
the spectra by decreasing the transmittance level. This case
12.4.1 Ifthemaximumabsorbanceofthecarbonylregionof
mayrequireadilutionasdescribedin12.4inordertoobtainan
the differential spectrum is higher than 1.5: dilute with 1 %
absorbance lower than 1.5.
accuracy by weight both fresh and aged oils with the same
14.3 Ester-Containing Oils—The ester functions contained
dilution factor, D (PAO 4 is recommended as dilution oil). For
in some lubricants, especially those formulated with ester base
example,D=2fora50% (1:1) wt/wt dilution. Record the two
oil, interfere with the oxidation peak. Dilution may be needed
spectra, convert them to absorbance and subtract them. If the
with these types of lubricants and it is recommended to use a
maximumabsorbanceofthecarbonylregionisstillhigherthan
cell with a small pathlength (0.05 mm maximum). Check the
1.5, then use a higher dilution factor. This occurrence could
shape of the spectrum before interpreting it. The residual
happen in the case of ester or soot-containing oil
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7214 − 07a (Reapproved 2012) D7214 − 07a (Reapproved 2019)
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),
technical committee LM5 and “Coordinating European Council” (CEC) Surveillance Group T-048 for
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
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
-1 -1
of 1600–18001600 cm to 1800 cm . 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
E131 Terminology Relating to Molecular Spectroscopy
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.96.03 on FTIR Testing Practices and Techniques Related to In-Service Lubricants.
Current edition approved Nov. 1, 2012Dec. 1, 2019. Published November 2012December 2019. Originally approved in 2006. Last previous edition approved in 20072012
as D7214–07a. –07a (2012). DOI: 10.1520/D7214-07AR12.10.1520/D7214-07AR19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7214 − 07a (2019)
E1421 Practice for Describing and Measuring Performance of Fourier Transform Mid-Infrared (FT-MIR) Spectrometers: Level
Zero and Level One Tests
E1866 Guide for Establishing Spectrophotometer Performance Tests
2.2 CEC Standard:
CEC L-48-A-00 Oxidation Stability of Lubricating Oils Used in Automotive Transmissions by Artificial Aging
3. Terminology
3.1 Definitions—For terminology relating to molecular spectroscopic methods, refer to Terminology E131.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 carbonyl region, n—region of the FT-IR spectrum corresponding to the absorbance of compounds containing a carbonyl
-1
function. Depending on the nature of the carbonyl compounds, this region is usually located between approximately 1820 cm and
-1
1650 cm .
3.2.2 differential spectrum, n—FT-IR absorbance spectrum resulting from the subtraction of the fresh oil from the used oil.
3.2.3 PAI (peak area increase), n—area of the carbonyl region of the differential FT-IR spectrum, divided by the cell pathlength
in millimetres. In this standard, PAI refers to a relative measurement of the oxidation of a used lubricant by FT-IR.
4. Summary of Test Method
4.1 FT-IR spectra of the fresh oil and of the used oil are recorded in a transmission cell of known pathlength. Both spectra are
converted to absorbance and then subtracted. Using this resulting differential spectrum, a baseline is set under the peak
-1 -1
corresponding to the carbonyl region around 1650 cm and 1820 cm and the area created by this baseline and the carbonyl peak
is calculated. The area of the carbonyl region is divided by the cell pathlength in millimetres and this result is reported as Peak
Area Increase (PAI).
5. 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.
6. Interferences
6.1 Some specific cases (very viscous oil, use of ester as base stock, high soot content) may require a dilution of the sample
and a specific area calculation, which are described in 14.1 – 14.3. In those cases, the result is corrected by a dilution factor, which
is applied to the sample.
7. Apparatus
-1 -1
7.1 FT-IR Spectrophotometer, suitable for recording measurements between 1650 cm and 1820 cm and with a resolution of
-1
4 cm .
7.2 Transmission Cell, with windows of potassium bromide, having a known pathlength of approximately 0.0250.025 mm to
0.1 mm.0.1 mm.
7.3 Syringe, or Other Automated or Semi-Automated Device, with adequate volume to fill the cell, for example, 2 mL.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
8.2 Heptane, used as cleaning solvent. Other solvents and solvent mixtures may be used provided they adequately clean the
cell(s) between samples. A 50/50 mixture of cyclohexane and toluene has been found to be useful in cleaning cells after highly
contaminated and degraded samples have been run. (Warning—Flammable.)
8.3 PAO4, used as dilution oil (PAO4: PolyAlphaOlefin with a kinematic viscosity at 100°C100 °C of approximately 4
mm4 mm /s)
Available from Coordinating European Council (CEC), c/o Interlynk Administrative Services, Ltd., P.O. Box 6475, Earl Shilton, Leicester, LE9 9ZB, U.K.
D7214 − 07a (2019)
9. Calibration and Standardization
9.1 Calculation of the Cell Pathlength—Use a cell with a known pathlength of approximately 0.0250.025 mm to 0.1 mm.
0.1 mm. Calibrate the infrared cell pathlength using the interference fringe method:
9.1.1 Acquire the single beam background infrared spectrum. Using the empty infrared cell in the infrared spectrometer sample
compartment, acquire the cell single beam infrared spectrum. Calculate the transmittance spectrum by dividing the cell single beam
spectrum by the background single beam spectrum. Optionally, convert the transmittance spectrum to an absorbance spectrum by
taking the negative logarithm (base 10) of the transmittance spectrum. The fringe calculation may be done on either the
transmittance or absorbance. spectrum. The final spectrum is obtained by subtraction of the background spectrum from the cell
spectrum.
NOTE 1—This computation is generally an integral part of the infrared spectrometer software.
9.1.2 Choose 2 minima separated by about 20 measurable interference fringes as shown in Fig. 1. Count the number of
interference fringes between the lower and the higher wavenumbers, referred to as λ and λ .
1 2
NOTE 2—The spectral range may be chosen freely in an area where the fringes are regular.
9.1.3 The cell pathlength is calculated by the formula:
5·n
e 5 (1)
λ 2 λ
~ !
1 2
where:
e = the pathlength in mm, and
n = the number of fringes between λ and λ .
1 2
9.2 Instrument Performance Checks:
9.2.1 Periodically, the performance of the FT-IR instrument should be monitored using the Level 0 procedure of Practice E1421.
If significant change in performance is noted, then testing should be suspended until the cause of the performance change is
diagnosed and corrected.
9.2.2 Alternative instrument performance tests conforming to the recommendations of Guide E1866 may be substituted for the
Practice E1421 test.
FIG. 1 Example of Interference Fringes for Cell Pathlength Calculation
D7214 − 07a (2019)
10. Conditioning
10.1 Before using the infrared cell ensure that it is clean by washing through with a suitable solvent, for example, heptane. Dry
the cell using dry air or nitrogen, if necessary. Calibrate this cell as described in Section 9.
11. Preparation of Sample of Used Oil
11.1 Refer to Practice D4057 (Manual Sampling) or Practice D4177 (Automatic Sampling) for proper sampling techniques.
11.2 When sampling used lubricants, the specimen shall be representative of the system sampled and shall be free of
contamination from external sources. As used oil can change appreciably in storage, test samples as soon as possible after removal
from the lubricating system and note the dates of sampling and testing.
11.3 If the sample of used oil contains visible sediment, heat to 6060 °C 6 5°C5 °C in the original container and agitate until
all of the sediment is homogeneously suspended in the oil. If the original container is a can or if it is glass and more than
three-fourths full, transfer the entire sample to a clear-glass bottle having a capacity at least one third greater than the volume of
the sample. Transfer all traces of sediment from the original container to the bottle by vigorous agitation of portions of the sample
in the original container.
12. Procedure
12.1 Acquire a single beam background spectrum. This background spectrum may be used in the conversion of all subsequent
spectra for at least one day.
12.2 With a syringe or other injection device, fill the cell with the fresh oil, and record its single beam sample spectrum. Convert
this spectrum to a transmittance spectrum by dividing it by the single beam background spectrum and to a fresh oil absorbance
spectrum by taking the negative logarithm (base 10) of the transmittance spectrum. Accumulate an adequate number of scans for
-1
a satisfactory noise level of < 2 mAbs @2000 @ 2000 cm .
-1 -1
NOTE 3—Assuming there are no absorbance peaks in the range from 20502050 cm to 1950 cm1950 cm for the sample, the noise level may be
estimated as the standard deviation of the absorbance data over this spectral range.
12.3 Empty and clean the cell. Heptane may be used. Fill the cell with the aged oil, and record its single beam sample spectrum.
Convert this spectrum to a transmittance spectrum by dividing by the single beam background spectrum, and to an aged oil
absorbance spectrum by taking the negative logarithm (base 10) of the transmittance spectrum.
NOTE 4—It may happen that the aged oil is too viscous to fill the cell. Then it is possible to proceed to a dilution as described in 12.4.1.
12.4 Generate a differential spectrum by subtracting the fresh oil absorbance spectrum from the aged oil absorbance spectrum
-1
(see Fig. 2). Locate and zoom on the carbonyl region centered at 1720 cm . Processing may continue if the maximum absorbance
of this carbonyl region is lower than 1.5.
-1 -1
NOTE 5—Since the carbonyl region absorption minima (close to 1820 cm1820 cm and 1650 cm1650 cm ) can vary with the type of oil sample being
tested, it was decided not to use fixed baseline limits for calculating the area A.
NOTE 6—The carbonyl band may consist of more than one peak maxima.
NOTE 7—Do not calculate the differential peak area by difference of the peak area of the aged oil with the peak area of the fresh oil.
FIG. 2 Area of Spectrum Showing the Result of the Automatic Subtraction by Computer of Aged Oil Spectrum and Fresh Oil Spectrum
D7214 − 07a (2019)
12.4.1 If the maximum absorbance of the carbonyl region of the differential spectrum is higher than 1.5: dilute with 1 %
accuracy by weight both fresh and aged oils with the same dilution factor, D (PAO 4 is recommended as dilution oil). For example,
D = 2 for a 50 % (1:1) wt/wt dilution. Record the two spectra, convert them to absorbance and subtract them. If the maximum
absorbance of the carbonyl region is still higher than 1.5, then use a higher dilution factor. This occurrence could happen in the
case of ester or soot-containing oils.
NOTE 8—The cell pathlength may be changed to 0.05 mm or 0.025 mm if absorbance in the assessment area is greater than 1.5.
NOTE 9—Dilution factors are commonly chosen between 2 and 10.
12.4.2 I
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