ASTM D7371-14(2022)

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.
Designation: D7371 − 14 (Reapproved 2022)
Standard Test Method for
Determination of Biodiesel (Fatty Acid Methyl Esters)
Content in Diesel Fuel Oil Using Mid Infrared Spectroscopy
(FTIR-ATR-PLS Method)
This standard is issued under the fixed designation D7371; 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 D1298 Test Method for Density, Relative Density, or API
Gravity of Crude Petroleum and Liquid Petroleum Prod-
1.1 This test method covers the determination of the content
ucts by Hydrometer Method
of fatty acid methyl esters (FAME) biodiesel in diesel fuel oils.
D4052 Test Method for Density, Relative Density, and API
It is applicable to concentrations from 1.00 % to 20 % by
Gravity of Liquids by Digital Density Meter
volume (see Note 1). This procedure is applicable only to
D4057 Practice for Manual Sampling of Petroleum and
FAME. Biodiesel in the form of fatty acid ethyl esters (FAEE)
Petroleum Products
will cause a negative bias.
D4177 Practice for Automatic Sampling of Petroleum and
NOTE 1—Using the proper ATR sample accessory, the range may be
Petroleum Products
expanded from 1 % to 100 % by volume, however precision data is not
D4307 Practice for Preparation of Liquid Blends for Use as
available above 20 % by volume.
Analytical Standards
1.2 The values stated in SI units of measurement are to be
D4737 Test Method for Calculated Cetane Index by Four
regarded as the standard. The values given in parentheses are
Variable Equation
for information only.
D5854 Practice for Mixing and Handling of Liquid Samples
1.3 This standard does not purport to address all of the
of Petroleum and Petroleum Products
safety concerns, if any, associated with its use. It is the D6299 Practice for Applying Statistical Quality Assurance
responsibility of the user of this standard to establish appro-
and Control Charting Techniques to Evaluate Analytical
priate safety, health, and environmental practices and deter- Measurement System Performance
mine the applicability of regulatory limitations prior to use.
D6751 Specification for Biodiesel Fuel Blend Stock (B100)
1.4 This international standard was developed in accor-
for Middle Distillate Fuels
dance with internationally recognized principles on standard- D7467 Specification for Diesel Fuel Oil, Biodiesel Blend
ization established in the Decision on Principles for the
(B6 to B20)
Development of International Standards, Guides and Recom- E168 Practices for General Techniques of Infrared Quanti-
mendations issued by the World Trade Organization Technical
tative Analysis
Barriers to Trade (TBT) Committee. E1655 Practices for Infrared Multivariate Quantitative
Analysis
2. Referenced Documents E2056 Practice for Qualifying Spectrometers and Spectro-
photometers for Use in Multivariate Analyses, Calibrated
2.1 ASTM Standards:
Using Surrogate Mixtures
D975 Specification for Diesel Fuel
D976 Test Method for Calculated Cetane Index of Distillate
3. Terminology
Fuels
3.1 Definitions:
3.1.1 biodiesel, n—a fuel comprised of mono-alkyl esters of
long chain fatty acids derived from vegetable oils or animal
This test method is under the jurisdiction of ASTM Committee D02 on
fats, designated B100. D6751
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0F on Absorption Spectroscopic Methods.
3.1.2 biodiesel blend, BXX, n—a blend of biodiesel fuel
Current edition approved July 1, 2022. Published August 2022. Originally
with petroleum-based diesel fuel. D7467
approved in 2007. Last previous edition approved in 2014 as D7371 – 14. DOI:
3.1.2.1 Discussion—In the abbreviation BXX, the XX rep-
10.1520/D7371-14R22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
resents the volume percentage of biodiesel fuel in the blend.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
D6751
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.1.3 diesel fuel, n—petroleum-based middle distillate fuel.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7371 − 14 (2022)
3.1.4 multivariate calibration, n—process for creating a water vapor can appear in the infrared spectrum. This shall be
model that relates component concentrations or properties to accounted for to permit calibration at the low end concentra-
the absorbances of a set of known reference samples at more tions.
NOTE 2—Ideally, the spectrometer should be purged with dry air or
than one wavelength or frequency. E1655
nitrogen to remove water vapor. The purge should be allowed to stabilize
3.1.4.1 Discussion—The resultant multivariate calibration
over several hours before analytical work is pursued, due to the rapid
modelisappliedtotheanalysisofspectraofunknownsamples
changes in the air moisture content within the spectrometer during early
to provide an estimate of the component concentration or
stages of the purge. In cases where water vapor prevention or elimination
property values for the unknown sample. is not possible using a purge, the operator should measure a reference
background spectrum for correction of the ratioed spectrum for each
3.1.4.2 Discussion—The multivariate calibration algorithm
sample spectrum measured. This operation is generally automated in
employed in this test method is partial least square (PLS) as
today’s spectrometer systems and the operator should consult the manu-
defined in Practices E1655.
facturer of the spectrometer for specific instructions for implementing
automated background correction routines. The spectrometer should be
3.2 Abbreviations:
sealedanddesiccatedtominimizetheaffectofwatervaporvariations,and
3.2.1 ATR—attenuated total reflectance
any accessory should be sealed to the spectrometer.
3.2.2 Bxx—see 3.1.2
6.4 Fatty Acid Ethyl Esters (FAEE) Interference—The pres-
3.2.3 FAEE—fatty acid ethyl esters
ence of FAEE in the composition of the biodiesel will result in
an overall lower concentration measurement of biodiesel
3.2.4 FAME—fatty acid methyl esters
content. Outlier statistical results may be a useful tool for
3.2.5 FTIR—Fourier transform infrared
determining high concentration FAEE content (for additional
3.2.6 mid-IR—mid infrared
FAEE information, see research report referenced in Section
3.2.7 PLS—partial least square
15).
3.2.8 ULSD—ultra low sulfur diesel
6.5 Undissolved Water—Samples containing undissolved
water will result in erroneous results. Filter cloudy or water
4. Summary of Test Method
saturated samples through a dry filter paper until clear prior to
their introduction into the instrument sample cell.
4.1 A sample of diesel fuel, biodiesel, or biodiesel blend is
introduced into a liquid attenuated total reflectance (ATR)
7. Apparatus
sample cell. A beam of infrared light is imaged through the
7.1 Mid-IR Spectrometric Analyzer:
sample onto a detector, and the detector response is deter-
7.1.1 Fourier Transform Mid-IR Spectrometer—The type of
mined. Wavelengths of the absorption spectrum that correlate
apparatus suitable for use in this test method employs an IR
highly with biodiesel or interferences are selected for analysis.
source, a liquid attenuated total internal reflection cell, a
A multivariate mathematical analysis converts the detector
scanning interferometer, a detector, an A-D converter, a
response for the selected areas of the spectrum from an
microprocessor, and a method to introduce the sample. The
unknown to a concentration of biodiesel.
following performance specifications shall be met:
4.2 This test method uses Fourier transform mid-IR spec-
-1 -1
Scan Range 4000 cm to 650 cm
trometer with an ATR sample cell. The absorption spectrum
-1
Resolution 4 cm
shall be used to calculate a partial least square (PLS) calibra-
7.1.2 The noise level shall be established by acquiring a
tion algorithm.
single beam spectrum using air or nitrogen. The single beam
spectrum obtained can be the average of multiple of FTIR
5. Significance and Use
scans but the total collection time shall not exceed 60 seconds.
5.1 Biodieselisablendstockcommodityprimarilyusedasa
If interference from water vapor or carbon dioxide is a
value-added blending component with diesel fuel.
problem, the instrument shall be purged with dry air or
nitrogen.Thenoiseofthespectrumat100 %transmissionshall
5.2 This test method is applicable for quality control in the
-1 -1
be less than 0.3 % in the region from 1765 cm to 1725 cm .
production and distribution of diesel fuel and biodiesel blends
containing FAME.
7.2 Absorption Cell, multi-bounce (multi-reflections) at-
tenuated total reflectance cell. It shall meet one of the follow-
6. Interferences
ing requirements:
7.2.1 Conical Attenuated Total Reflectance (ATR) Cell,
6.1 The hydrocarbon composition of diesel fuel has a
having similar specifications defined in Table 1. This cell is
significant impact on the calibration model. Therefore, for a
suitable for the low, medium, and high concentration ranges.
robust calibration model, it is important that the diesel fuel in
7.2.2 Horizontal Attenuated Total Reflectance (ATR) Cell,
the biodiesel fuel blend is represented in the calibration set.
with ZnSe element ATR mounted on a horizontal plate. The
6.2 Proper choice of the apparatus, design of a calibration -1
absorbance at 1745 cm shall not exceed 1.2 absorbance units
matrix, utilization of multivariate calibration techniques, and
for the highest concentration calibration standard used in the
evaluation routines as described in this standard can minimize
calibration range. Therefore, for higher concentration
interferences.
measurements, careful consideration of element length and
6.3 Water Vapor Interference—The calibration and analysis face angle shall be made to maximize sensitivity without
-1
bands in A1.2 lie in regions where significant signals due to exceeding 1.2 absorbance units at 1745 cm .
D7371 − 14 (2022)
TABLE 1 Attenuated Total Reflectance (ATR) Conical
8.1.3 Diesel Cetane Check Fuel—Low (DCCF-Low). (See
Cells Specification
A2.2 for alternative material.)
ATR element material ZnSe
8.1.4 Diesel Cetane Check Fuel—High (DCCF-High).
beam condensing optics conical, non-focusing optics
8.1.5 Diesel Cetane Check Fuel—Ultra High (DCCF-Ultra
integral to cell body
High).
element configuration circular cross section with
coaxial conical ends
8.1.6 Acetone [67-64-1]—Reagent grade.
cone half angle 60°
8.1.7 Toluene [108-88-3]—Reagent grade.
element length 36.83 mm to 39.37 mm (1.45 in.
to 1.55 in.) 8.1.8 Methanol [67-56-1]—Reagent grade.
element diameter 3.175 mm (0.125 in.)
8.1.9 Triple Solvent—Amixture of equal parts by volume of
angle of incidence at sample 53.8°
toluene, acetone, and methanol.
interface
maximum range of incidence ± 1.5°
angles
9. Sampling and Sample Handling
standard absorbance 0.38 AU ± 0.02 AU
-1
(1428 cm band of acetone)
9.1 General Requirements:
material of construction 316 stainless steel
9.1.1 Fuel samples to be analyzed by this test method shall
A
seals Chemrez or Kalrez o-rings
be sampled using procedures outlined in Practice D4057 or
A
Trademarks of Chemrez, Inc. and Dupont Performance Elastomers L.L.C.
Practice D4177, where appropriate. Do not use “sampling by
water displacement.” FAME is more water-soluble than the
hydrocarbon base in a biodiesel blend.
9.1.2 Protect samples from excessive temperatures prior to
testing.
8. Reagents and Materials
9.1.3 Donottestsamplesstoredinleakycontainers.Discard
8.1 Purity of Reagents—Spectroscopic grade (preferred) or and obtain a new sample if leaks are detected.
reagent grade chemicals shall be used in tests. Unless other-
9.2 Sample Handling During Analysis:
wise indicated, it is intended that all reagents shall conform to
9.2.1 When analyzing samples using the FTIR, the sample
thespecificationsofthecommitteeonanalyticalreagentsofthe
temperature needs to be within the range of 15 °C to 27 °C.
American Chemical Society, where such specifications are
Equilibrate all samples to the temperature of the laboratory
available. Other grades may be used, provided it is first
(15 °C to 27 °C) prior to analysis by this test method.
ascertained that the reagent is of sufficiently high purity to
9.2.2 After analysis, if the sample is to be retained, reseal
permit its use without lessening the accuracy of the determi- the container before storing.
nation.
10. Calibration and Qualification of the Apparatus
8.1.1 B100 (Neat Biodiesel)—Used for calibration,
qualification, and quality control standards shall be compliant
10.1 Before use, the instrument needs to be calibrated
with Specification D6751. The B100 shall be fatty acid methyl
according to the procedure described in Annex A1. This
esters. Soy methyl ester (SME) was used in calibration
calibration can be performed by the instrument manufacturer
standards for developing the precision of this test method. prior to delivery of the instrument to the end user. If, after
Esters derived from other feedstocks, for example animal fats, maintenance, the instrument calibration is repeated, the quali-
canola oil, jatropha oil, palm oil, rapeseed oil, and yellow fication procedure is also repeated.
grease may be used. Standards made with yellow grease
10.2 Before use, the instrument is qualified according to the
methyl esters should not represent more than 50 % of the
procedure described in AnnexA1. The qualification need only
number of the calibration standards. A BQ-9000 certified
be carried out when the instrument is initially put into
producer for the biodiesel is recommended to ensure quality of
operation, recalibrated, or repaired.
product. See Annex A2 for further discussion.
8.1.2 Middle Distillate Fuel—Used for calibration, 11. Quality Control Checks
qualification, and quality control standards shall be compliant
11.1 Confirm the in-statistical-control status of the test
with Specification D975, free of biodiesel or biodiesel oil
method each day it is used by measuring the biodiesel
precursor, or both. As far as possible, middle distillate fuel
concentration of at least one quality control sample that is
shall be representative of petroleum base stocks anticipated for
similar in composition and matrix to samples routinely ana-
blends to be analyzed (crude source, 1D, 2D, blends, winter/
lyzed. For details on quality control sample selection,
summer cuts, low aromatic content, high aromatic content, and
preparation, testing, and control charting, refer to Practice
the like). See Annex A2 for calibration set.
D6299.
3 4
ACS Reagent Chemicals, Specifications and Procedures for Reagents and The sole source of supply of the material known to the committee at this time
Standard-Grade Reference Materials, American Chemical Society, Washington, is Chevron Phillips Chemical Company LLC, 10001 Six Pines Drive, The
DC. For suggestions on the testing of reagents not listed by theAmerican Chemical Woodlands,TX 77380. If you are aware of alternative suppliers, please provide this
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, information to ASTM International Headquarters. Your comments will receive
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma- careful consideration at a meeting of the responsible technical committee, which
copeial Convention, Inc. (USPC), Rockville, MD. you may attend.
D7371 − 14 (2022)
-1
11.2 A system that is found to be out of statistical control (see A1.2.4.2) to the spectrum in the region of 1800 cm to
-1 -1 -1
cannot be used until the root cause(s) of out-of-control is 1700 cm and 1399 cm to 931 cm using no baseline
identified and corrected. correction.
12.7.1.4 Ifthevalueestimatedbyapplicationofthemedium
11.3 If correction of out-of-control behavior requires repair
calibration determined in 12.7.1.3 is less than or equal to
to the instrument or recalibration of the instrument, the
10.50 % by volume, report the value determined by the low
qualificationofinstrumentperformancedescribedinA1.3shall
calibration (even if the value is greater than 10.5 % by
be performed before the system is used to measure the
volume). For estimated values greater than 10.50 % by volume
biodiesel content of samples.
and less than or equal to 30.00 % by volume determined in
12.7.1.3, report the value obtained.
12. Procedure
12.7.1.5 If the estimated biodiesel concentration determined
12.1 Equilibrate the samples to between 15 °C and 27 °C
in 12.7.1.4 is greater than 31.00 % by volume, estimate the
before analysis.
biodiesel concentration by applying the high calibration (see
-1
A1.2.4.3) to the spectrum in the region of 1851 cm to
12.2 Clean the sample cell of any residual fuel according to
-1 -1 -1
1670 cm and 1371 cm to 1060 cm using no baseline
the manufacturer’s instructions. Remove the fuel by flushing
correction.
the cell with sufficient solvent or the subsequent sample to
12.7.1.6 If the value estimated by application of the high
ensure complete washing. For difficult to remove substances
calibration determined in 12.7.1.5 is less than or equal to
like B100, precede flushing with triple solvent. Evaporate the
31.00 % by volume, report the value determined by the
residual solvent with either dry air or nitrogen.
medium calibration (even if the value is greater than 31.00 %
12.3 Obtain a baseline spectrum in the manner established
by volume). For estimated values greater than 31.00 % by
by the manufacturer of the equipment.
volume (determined in 12.7.1.5), report the value obtained.
12.4 Priortotheanalysisofunknowntestsamples,establish
NOTE 4—Clean cell thoroughly after use. Occasionally, clean cell of
that the equipment is running properly by collecting the
any water soluble substances by first cleaning with acetone. Place a
spectrum of the quality control standard(s) and comparing the solution of 30 % alcohol (ethyl or methyl) in water in the cell and let it
soak for at least one hour. Finally, clean cell with acetone and dry. No
estimated biodiesel concentration(s) to the known value(s) for
acids or bases should be used in cleaning ZnSe elements.
the QC standard(s). Introduce enough standard into the cell to
ensure that the cell is washed by at least three times the cell
13. Calculation
volume.
13.1 Conversion to Volume % of Biodiesel—To convert the
12.5 Introduce the unknown fuel sample in the manner
calibration and qualification standards to volume % use Eq 1.
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