ASTM D7419-07

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D7419 − 07
StandardTest Method for
Determination of Total Aromatics and Total Saturates in
Lube Basestocks by High Performance Liquid
Chromatography (HPLC) with Refractive Index Detection
This standard is issued under the fixed designation D7419; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 aromatics, n—in high performance liquid
chromatography, aromatic hydrocarbon components, minus
1.1 This test method covers the determination of total
polarmaterial,thathasalongerretentiontimethansaturateson
aromatics and total saturates in additive-free lube basestocks
the specified polar columns, but can be removed as a single
using high performance liquid chromatography (HPLC) with
peak by backflushing the columns with heptane.
refractive index (RI) detection. This test method is applicable
3.1.1.1 Discussion—Generally, aromatic hydrocarbons con-
to samples containing total aromatics in the concentration
tain 1 to 4 rings.
range of 0.2 to 46 mass%.
3.1.2 backflush, v—elutionoftheHPLCmobilephaseinthe
1.1.1 Polar compounds, if present, are combined with the
backward or reverse direction from the silica gel column
total aromatics. Precision was determined for basestocks with
towards the cyano column.
polars content < 1.0 mass%.
3.1.2.1 Discussion—In this test method, it is used to elute
1.2 The values stated in SI units are to be regarded as
the total aromatics plus polars as one sharp component.
standard. No other units of measurement are included in this
3.1.3 foreflush, v—elution of HPLC mobile phase in the
standard.
forward direction.
1.3 This standard does not purport to address all of the
3.1.3.1 Discussion—In this test method, the sample enters
safety concerns, if any, associated with its use. It is the
the cyano column first followed by elution through the silica
responsibility of the user of this standard to establish appro-
gel column.
priate safety and health practices and determine the applica-
3.1.4 polars, n—in high performance liquid
bility of regulatory limitations prior to use.
chromatography, components that may contain organically
2. Referenced Documents
bonded nitrogen, oxygen and oxidized sulfur components and
2 are more strongly retained than aromatic hydrocarbons.
2.1 ASTM Standards:
3.1.4.1 Discussion—In this HPLC method, polars are back-
D4057Practice for Manual Sampling of Petroleum and
flushedwiththearomaticsandthetwocannotbedistinguished.
Petroleum Products
Generally present in very small amounts, such as < 1 mass%.
D4177Practice for Automatic Sampling of Petroleum and
3.1.5 saturates, n—hydrocarbon components that are not
Petroleum Products
D6299Practice for Applying Statistical Quality Assurance retained strongly by the specified polar columns when heptane
is used as the mobile phase.
and Control Charting Techniques to Evaluate Analytical
Measurement System Performance 3.1.5.1 Discussion—Generally, these consist of paraffins
and cycloparaffins.
3. Terminology
4. Summary of Test Method
3.1 Definitions:
4.1 Aknown mass of sample is diluted in the mobile phase
and a fixed volume of this solution is injected into a calibrated
This test method is under the jurisdiction of ASTM Committee D02 on
high performance liquid chromatograph. The separation col-
PetroleumProductsandLubricantsandisthedirectresponsibilityofSubcommittee
umn set has little affinity for the saturates while retarding the
D02.04.0C on Liquid Chromatography.
aromatic hydrocarbons and the polars. As a result of this
CurrenteditionapprovedDec.1,2007.PublishedFebruary2008.DOI:10.1520/
D7419-07.
retardation,thearomatichydrocarbonsandpolarsareseparated
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
fromthesaturates.Atapredeterminedtime,aftertheelutionof
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the saturates, the column is backflushed to elute the aromatics
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. and polars as a single sharp band.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7419 − 07
4.2 The column set is connected to a refractive index 6.5.1 UV-Detector—An optional but recommended UV de-
detector that detects the components as they elute from the tectorsettowavelength254nmmaybeusedinserieswiththe
column. The electronic signal from the detector is continually RI detector to aid in setting and monitoring the backflush time
monitored by a data processor. The integrated signals (peak between saturates and aromatics in lube samples.
areas) from the saturates and aromatics components are cor-
6.6 Computer or Computing Integrator—Any data system
rected using a predetermined response factor and the mass%
can be used provided it is compatible with the refractive index
saturates and aromatics plus polars are calculated.
detector, has a minimum sampling rate of 1 Hz and is capable
of peak area and retention time measurement.The data system
5. Significance and Use
shall have minimum capabilities for post-analysis data
5.1 Thecompositionofalubricatingoilhasalargeeffecton
processing, such as automatic or manual baseline correction
the characteristics and uses of the oil. The determination of
and reintegration.
saturates, aromatics and polars is a key analysis of this
6.7 Volumetric Flasks—Grade B or better, of 10 mL capac-
composition. The characterization of the composition of lubri-
ity.
cating oils is important in determining their interchangeability
6.8 Autosampler Vials—per instrument manufacturer. Vials
for use in blending etcetera.
with a capacity of >1.5 mL have been used successfully.
6. Apparatus
6.9 Analytical Balance—accurate to 60.0001 g.
6.1 High Performance Liquid Chromatograph (HPLC)—
7. Reagents and Materials
Any HPLC capable of pumping the mobile phase at flow rates
7.1 Heptane, HPLC grade. If necessary, dry solvent with
between 3 and 5 mL/min, with a precision better than 0.5%.
molecular sieves and then filter before use.
6.2 HPLC Sample Injection System—Capable of injecting
7.2 Dichloromethane, HPLC or UVgrade. If necessary, dry
10 µL(nominal) of sample solution with a repeatability of 1%
solvent with molecular sieves and then filter before use.
or better.
7.3 Octadecylbenzene, ≥ 97% pure.
6.3 Column System—A column set is used. Any stainless
steelHPLCcolumnpackedwithsilicagelstationaryphasethat
7.4 Hexadecane, ≥ 98% pure.
meetstheresolutionandcapacityrequirementsspecifiedin9.3
8. Sampling
is suitable. Use a single silica column or two connected in
series with a total length of 500 mm with an internal diameter
8.1 Follow Practice D4057 or D4177, or a similar standard
of7.5to10mmandpackedwith5µmparticlesize.Inaddition
to obtain a representative laboratory sample of the basestock.
tothesilicacolumn,anHPLCcolumnpackedwithcyano(CN)
Mix well before sampling.
stationary phase is required and placed in series in front of the
silica column.ACN column length of 100 to 250 mm with an 9. Preparation of Apparatus
internal diameter of 7.7 to 10 mm and packed with 5 to 10 µm
9.1 Set up the liquid chromatograph, injection system,
particlesizestationaryphasehasbeenfoundtobesatisfactory.
columns, backflush valve, optional column oven, optional UV
Table 1 gives examples of column sets used in the cooperative
detector, refractive index detector and computing integrator in
study.
accordance with the manufacturer’s instructions and as de-
6.4 Backflush Valve—Automatic flow-switching valve de- picted in Fig. 1. Insert the backflush valve so that the detector
signed for use in HPLC systems that is capable of operating at is always connected independently of the direction of flow
pressures up to2×10 kPa. through the column (see Fig. 1). Maintain the sample injection
valve at the same temperature as the sample solution; in most
6.5 Refractive Index Detector—Any refractive index detec-
cases this will be at room temperature. To minimize drifts in
tor may be used provided it is capable of being operated over
signal, ensure that the ambient temperature is relatively con-
the refractive index range from 1.3 to 1.6 or equivalent, meets
stant during analysis and calibration.
thesensitivityandlinearityofcalibrationrequirementspecified
in the method and has a suitable output signal for the data 9.2 New commercial columns may be packed in water/
system. If the refractive index detector has a facility for methanol or other polar solvents. Before these columns can be
independent temperature control, it is recommended that this used flush them with dichloromethane followed with heptane
be set at 5°C above the laboratory temperature. before proceeding. Other suitable solvents that restore the
TABLE 1 Examples of Operating Conditions Used in Cooperative Studies
Lab A Lab B Lab C
Silica Column Varian, 50 cm length by 7.7 mm i.d. 5 µm Si60 Varian, 50 cm by 7.7 mm Si60 (CP28526) Phenomenex, 2 x Si60 (10 by 250 mm, 5 µm
Cyano Column Alltech//YMC, 100 by 10 mm 10 µm Waters/YMC, 100 by 12 mm 5 µm YMC, 10 by 100 mm 5 µm
RI Detector Agilent 1200 Hewlett Packard RI, model HP1047A Shimadzu RID-10A
Heptane Flow (mL/min) 3.5 mL/min 3.0 3.0
Resolution 5 5-6 10.3
Injected Volume (microlitres) 10 10 10
D7419 − 07
FIG. 1 Diagrammatic Representation of Liquid Chromatograph
required resolution may be used. If the resolution requirement that the octadecylbenzene is completely dissolved in the
is not met, the column may be reactivated by flushing it with mixture, for example, by using an ultrasonic bath.
additional dichloromethane. If the resolution still cannot be
9.3.2 When operating conditions are steady, as indicated by
attained it may be necessary to replace the column or purchase
a stable horizontal baseline of the RI detector, inject 10 µL of
an appropriate column from other vendors. Si60 silica gel was
the SPS in the foreflush mode (backflush valve = OFF) and
found effective in yielding acceptable resolution and perfor-
recordthechromatogramusingthedatasystem.Fig.2givesan
mance when properly conditioned. When not analyzing
example chromatogram of the SPS mixture.
samples, column may be flushed with a low flow of heptane
9.3.3 Ensure that the resolution between hexadecane and
such as 0.1 mL/min.
octadecylbenzene is five or greater as defined below. Calculate
9.2.1 Adjust the flow rate of the mobile phase to a constant
the resolution between hexadecane and octadecylbenzene as
3.0 to 3.5 mL/min, and ensure the reference cell of the
follows:
refractive index detector is full of mobile phase. Fill the
2 3 ~t 2 t !
2 1
reference cell as instructed by the manufacturer. Resolution 5 (1)
3 3 y 1y
~ !
1 2
9.2.2 To minimize drift, it is essential to make sure the
where:
referencecelloftheRIdetectorisfullofsolvent.Thebestway
to accomplish this is either (1) to flush the mobile phase
t = retention time of the hexadecane peak in minutes,
through the reference cell (then isolate the reference cell to
t = retentiontimeoftheoctadecylbenzenepeakinminutes,
prevent evaporation of the solvent) immediately prior to y = half-height width of the hexadecane peak in minutes,
analysis, or (2) to continuously make up for solvent evapora-
and
tion by supplying a steady independent flow through the y = half-height width of the octadecylbenzene peak in
referencecell.Themake-upflowisoptimizedsothatreference minutes.
andanalyticalcellmismatchduetodrying-out,temperature,or
If the resolution is less than five, verify that all system
pressure gradients is minimized. Typically, this can be accom-
components are functioning correctly and that the chromato-
plished with a make-up flow set at one tenth of the analytical
graphic dead volume has been minimized by using low dead
flow.
volume connectors, tubing etcetera. Ensure that the mobile
9.3 Column Resolution and Capacity Factor: phase is of sufficiently high quality. Finally, regenerate or
9.3.1 Prepare a system performance standard (SPS) by replace the column if necessary. The column may be regener-
weighing hexadecane (1.0 6 0.1g) and octadecylbenzene (1.0 ated by flushing with dichloromethane followed by heptane
6 0.1 g) into a 10 mLvolumetric flask and filling to the mark untilthesignalisrelativelyconstantontheRIdetector.Ifafter
with heptane. For the preparation of standards, use the same regenerating the silica columns, the resolution is still less than
sourcefortheheptaneasthatusedforthemobilephase.Ensure 5 then replace the silica columns. Si60 was found to be an
D7419 − 07
FIG. 2 Chromatogram of System Performance Standard in Foreflush Mode for Determination of Resolution, Capacity Factor and Back-
flush Time
effective silica gel with proper conditioning. For a proper 9.3.5 Using the determined retention times of the hexade-
analysis, a resolution of at least five is required. caneandoctadecylbenzenepeaksin9.3.2calculateanapproxi-
mate switching valve backflush time, B, in seconds, using the
NOTE 1—Resolution loss over time may occur if a heptane mobile
following equation:
phase of low water content is not used. Use heptane as specified in this
method. If necessary, dry the heptane with the addition of activated
B 5 t 10.1 3 t 2 t (3)
~ !
1 2 1
molecular sieves, such as MS 5Aand then filter with at least 0.45 micron
HPLC filter before use. where:
9.3.4 Calculate the capacity factor, k, for octadecylbenzene t = retention time of hexadecane in minutes, and
t = retention time of octadecylbenzene in minutes.
from 9.3.2 as follows:
9.4 Oncethebackflushtimeisdetermined,re-injecttheSPS
~t 2 t !
2 1
Capacity Factor 5 k 5 (2)
mixture with backflush in place and ensure that the backflush
t
~ !
time as observed as a signal marker on the chromatogram
where:
occurs at the base of the eluted saturate peak. The return to
t = retention time of the hexadecane peak in minutes,
1 baseline shall display as shown in Fig. 3, point B. This
t = retention time of the octadecylbenzene peak in minutes
observation shall be made also for all actual lube samples
Ensure that the capacity factor is > 0.4. analyzed. If necessary optimize, reconfirm the resolution and
FIG. 3 Chromatogram of System Performance Standard in Backflush Mode
D7419 − 07
capacity factor and recheck the backflush time. The use of the weighing, to the nearest 0.0001 g, the appropriate materials
optional UV detector will simplify optimization of the back- into 10-mL volumetric flasks and making up
...