ASTM D7591-12(2017)

Standard Test Method for Determination of Free and Total Glycerin in Biodiesel Blends by Anion Exchange Chromatography

SIGNIFICANCE AND USE
5.1 Petroleum-based diesel may be blended with biodiesel. High levels of free glycerin in biodiesel can cause injector deposits (“gel effect”), as well as clogging fuel systems. High levels of unreacted glycerides can cause injector deposits and can adversely affect cold weather operation and filter plugging.
SCOPE
1.1 This test method covers and describes an anion exchange chromatography procedure for determining free and total glycerin content of biodiesel (B100) and blends (B0 to B20) with diesel fuel oils defined by Specification D975 Grades 1-D, 2-D, and low sulfur 1-D and 2-D and Specification D6751 (for B100 feedstocks). It is intended for the analysis of biodiesel and blend samples containing between 0.5 mg/kg to 50 mg/kg glycerin.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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.  
1.4 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.

General Information

• Status: Published
• Publication Date: 30-Apr-2017
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.04.0C - Liquid Chromatography

Relations

• Replaces: ASTM D7591-12 - Standard Test Method for Determination of Free and Total Glycerin in Biodiesel Blends by Anion Exchange Chromatography
• Effective Date: 01-May-2017
• Refers: ASTM D975-23a - Standard Specification for Diesel Fuel
• Effective Date: 15-Dec-2023
• Refers: ASTM D6299-23a - Standard Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
• Effective Date: 01-Dec-2023
• Refers: ASTM D6792-23c - Standard Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
• Effective Date: 01-Nov-2023
• Refers: ASTM D6792-23b - Standard Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
• Effective Date: 01-Oct-2023
• Refers: ASTM D975-19 - Standard Specification for Diesel Fuel Oils
• Effective Date: 01-Feb-2019
• Refers: ASTM D975-18a - Standard Specification for Diesel Fuel Oils
• Effective Date: 01-Dec-2018
• Refers: ASTM D6751-18 - Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
• Effective Date: 01-Oct-2018
• Refers: ASTM D975-17a - Standard Specification for Diesel Fuel Oils
• Effective Date: 15-Dec-2017
• Refers: ASTM D6299-17b - Standard Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
• Effective Date: 15-Dec-2017
• Refers: ASTM D6299-17a - Standard Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
• Effective Date: 15-Nov-2017
• Refers: ASTM D975-17 - Standard Specification for Diesel Fuel Oils
• Effective Date: 01-May-2017
• Refers: ASTM D6299-17 - Standard Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
• Effective Date: 01-Jan-2017
• Refers: ASTM D975-16a - Standard Specification for Diesel Fuel Oils
• Effective Date: 01-Oct-2016
• Refers: ASTM D975-16 - Standard Specification for Diesel Fuel Oils
• Effective Date: 01-Sep-2016

Overview

ASTM D7591-12(2017) is the standard test method developed by ASTM International for the determination of free and total glycerin in biodiesel and biodiesel blends using anion exchange chromatography. Accurate measurement of glycerin is essential for quality control in biodiesel production, as excess free glycerin or unreacted glycerides can cause operational issues such as injector deposits, filter clogging, and reduced cold weather performance in diesel engines. The method is applicable to biodiesel (B100) and blends from B0 to B20 with petroleum diesel fuels as defined by ASTM D975 and D6751.

Key Topics

• Scope: The method describes procedures for analyzing free and total glycerin content in biodiesel and its blends, targeting concentrations between 0.5 mg/kg and 50 mg/kg. Only SI units are used.
• Significance: High levels of glycerin in biodiesel can impair fuel systems, cause injector deposits, “gel effect”, filter plugging, and negatively affect cold weather operations.
• Definitions:
  • Free Glycerin: The amount of glycerin physically present in the fuel after production.
  • Total Glycerin: The sum of free glycerin and glycerin bound in unreacted or partially reacted oils or fats.
• Test Method Summary: Involves the use of ion chromatographic separation followed by quantitation based on an external calibration curve. Calibration is performed using pure glycerin standards prepared in water.

Applications

The ASTM D7591-12(2017) standard is widely used in several practical contexts:

• Biodiesel Quality Assurance: Ensures compliance with regulatory and industry limits for glycerin content in both neat biodiesel (B100) and blends (B0-B20).
• Blending Compliance: Used by fuel producers and distributors to verify conformity with ASTM D975 and D6751 specifications for diesel and biodiesel blends.
• Engine Protection: Prevents engine operational issues such as injector fouling, deposits, and filter plugging by allowing early detection of high glycerin content.
• Laboratory Testing: Utilized by petroleum laboratories and testing facilities practicing routine analysis and quality control for biodiesel products.
• Regulatory Reporting: Supports documentation for trade, export, or import of biodiesel and blends, as adherence to glycerin limits is often mandated by regulatory bodies.

Related Standards

The ASTM D7591-12(2017) standard references and is often used in conjunction with related international and ASTM standards, including:

• ASTM D975: Specification for Diesel Fuel Oils - defines petroleum diesel grades.
• ASTM D6751: Specification for Biodiesel Fuel Blend Stock (B100) - provides biodiesel feedstock requirements.
• ASTM D4057 / D4177: Practices for manual and automatic sampling of petroleum products.
• ASTM D1193: Specification for Reagent Water - outlines water purity requirements.
• ASTM D6299: Practice for Statistical Quality Assurance and Control Charting.
• ASTM D6792: Quality Management Systems in Petroleum Product Testing Laboratories.
• ASTM E177 / E691: Guidance on test precision and bias, and interlaboratory studies.

Practical Value

By using ASTM D7591-12(2017) for the determination of free and total glycerin in biodiesel blends, producers, laboratories, and regulatory agencies improve fuel reliability and performance while minimizing maintenance risks in diesel engines. This standard supports robust quality management in the renewable fuels sector, ensuring biodiesel meets both industry standards and regulatory requirements for safe and effective use. Compliance with this test method underpins customer confidence and marketability of biodiesel and its blends.

Keywords

biodiesel blends, free glycerin, total glycerin, anion exchange chromatography, ASTM D7591, diesel fuel quality, biodiesel testing, glycerin in biodiesel, fuel standards, quality control.

Standards Content (Sample)

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:D7591 −12 (Reapproved 2017)
Standard Test Method for
Determination of Free and Total Glycerin in Biodiesel
Blends by Anion Exchange Chromatography
This standard is issued under the fixed designation D7591; 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 D6299 Practice for Applying Statistical Quality Assurance
and Control Charting Techniques to Evaluate Analytical
1.1 This test method covers and describes an anion ex-
Measurement System Performance
change chromatography procedure for determining free and
D6751 Specification for Biodiesel Fuel Blend Stock (B100)
total glycerin content of biodiesel (B100) and blends (B0 to
for Middle Distillate Fuels
B20) with diesel fuel oils defined by Specification D975
D6792 Practice for Quality Management Systems in Petro-
Grades1-D,2-D,andlowsulfur1-Dand2-DandSpecification
leum Products, Liquid Fuels, and Lubricants Testing
D6751 (for B100 feedstocks). It is intended for the analysis of
Laboratories
biodiesel and blend samples containing between 0.5 mg⁄kg to
E177 Practice for Use of the Terms Precision and Bias in
50 mg⁄kg glycerin.
ASTM Test Methods
1.2 The values stated in SI units are to be regarded as
E691 Practice for Conducting an Interlaboratory Study to
standard. No other units of measurement are included in this
Determine the Precision of a Test Method
standard.
1.3 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 free glycerin, n—measure of the amount of glycerin
priate safety and health practices and determine the applica-
remaining in the fuel.
bility of regulatory limitations prior to use.
1.4 This international standard was developed in accor- 3.1.2 total glycerin, n—sum of the free glycerin and the
glycerin portion of any unreacted or partially reacted oil or fat.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4. Summary of Test Method
mendations issued by the World Trade Organization Technical
4.1 Free Glycerin—A small volume of an extract of the
Barriers to Trade (TBT) Committee.
blend sample is directly injected into an ion chromatograph
consisting of appropriate ion exchange columns and into an
2. Referenced Documents
electrochemical detector. Glycerin is separated based on its
2.1 ASTM Standards:
affinity for ion exchange sites of the resin with respect to the
D975 Specification for Diesel Fuel Oils
resin’s affinity for the eluent. An electrochemical detector is
D1193 Specification for Reagent Water
employed for detection of glycerin. Glycerin is quantified by
D4057 Practice for Manual Sampling of Petroleum and
peak area based on an external calibration curve, and is
Petroleum Products
reported as µg/g (mg/kg), or may be converted to wt%.
D4177 Practice for Automatic Sampling of Petroleum and
Calibration standards are prepared from commercially avail-
Petroleum Products
able glycerin (99+% purity) in an aqueous solution.
4.2 Total Glycerin—A small volume extract of a saponified
This test method is under the jurisdiction of ASTM Committee D02 on
blend sample is directly injected into an ion chromatograph
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
consisting of appropriate ion exchange columns and into an
Subcommittee D02.04.0C on Liquid Chromatography.
electrochemical detector. Glycerin is separated based on its
CurrenteditionapprovedMay1,2017.PublishedJuly2017.Originallyapproved
affinity for ion exchange sites of the resin with respect to the
in 2012. Last previous edition approved in 2012 as D7591 – 12.
DOI:10.1520 ⁄D7591-12R17.
resin’s affinity for the eluent. An electrochemical detector is
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
employed for detection of glycerin. Glycerin is quantified by
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
peak area based on an external calibration curve, and is
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. reported as µg/g (mg/kg), or may be converted to wt%.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7591−12 (2017)
FIG. 1Typical Chromatogram of a Solution Containing 0.7mg⁄kg of Glycerin
Calibration standards are prepared from commercially avail- 7. Apparatus
able glycerin (99+% purity) in an aqueous solution.
7.1 Analytical Balance—capable of weighing up to 200 g
accurately to 60.0001 g.
5. Significance and Use
7.2 Desiccator—containing freshly activated silica gel (or
5.1 Petroleum-based diesel may be blended with biodiesel.
equivalent desiccant) with moisture content indicator.
High levels of free glycerin in biodiesel can cause injector
deposits (“gel effect”), as well as clogging fuel systems. High
7.3 Pipettes or Volumetric Transfer Devices— 1 mL and
levels of unreacted glycerides can cause injector deposits and
5 mLclassAvolumetric pipettes or calibrated variable volume
can adversely affect cold weather operation and filter plugging.
automatic pipettes fitted with disposable polypropylene tips.
7.4 Volumetric Flasks—25 mL, 50 mL, 100 mL, and
6. Interferences
1000 mL class A volumetric flasks.
6.1 Interferences can be caused by substances with similar
7.5 Container—standard HDPE plastic 100 mL bottle with
ion chromatographic retention times, especially if they are in
cap.
high concentration compared to the analyte of interest. Sample
dilution can be used to minimize or resolve most interference
7.6 Ion Chromatograph—Analytical system with all re-
problems.Also,anexcessofunreactedhydroxide(base)during
quired accessories including syringes, columns, high-pressure
the sample preparation step for total glycerin can cause a pH
dual piston pump, and detector.
imbalance on the anion exchange column, resulting in a
7.6.1 Injection System—capable of delivering 5 µLto 25 µL
negative dip in front of the glycerin peak.
with a precision better than 1 %.
6.2 A water dip (system void, negative peak as shown in
7.6.2 Pumping System—capable of delivering mobile phase
Fig. 1) can cause interference with some integrators. This dip
flows between 0.1 mL⁄min and 5.0 mL⁄min with a precision
can be eliminated by dilution with the eluent. The water dip
better than 2 %. Due to the corrosive nature of the eluent, a
should not be a problem since the glycerin peak is resolved
PEEK pump head is recommended.
from the void peak.
7.6.3 Guard Column—for protection of the analytical col-
6.3 Interferences can be caused by contamination of
umn from strongly retained constituents.
glassware, eluent, reagents, etc. Take care to ensure that
7.6.4 Anion Exchange Column—capable of producing sat-
contamination is kept at the lowest possible levels. The use of
isfactory analyte separation.
nitrile gloves is highly recommended to prevent contamination
7.6.5 Electrochemical Detector—integrated, temperature
during sample preparation.
controlled to 0.1 °C, capable of measuring at least 0 µA to
6.4 There are several known additives based on natural
200 µA on a linear scale. Detector has a pulsed amperometric
products that might have similar retention times and detector
detection mode for required sensitivity. Consult with the
response similar to glycerin. In the case of higher than
manufacturer for optimal cell settings.
expected values for biodiesel blends, it is highly recommended
7.6.6 Electrochemical Detector Cell—minimum 3 mm gold
that the user needs to verify these higher than expected values
working electrode surface with wall jet design, solid state
for glycerin using a different analytical technique.
reference and counter electrodes. Ensure a minimal volume in
6.5 Pre-rinsing of the sample preparation containers with the cell for enhanced sensitivity.Aplatinum working electrode
deionized water is mandatory. may also be used.
D7591−12 (2017)
TABLE 1 Preparation of Glycerin Standards in Water
7.6.7 Integrator or Chromatography Data System
Software—capable of measuring peak areas and retention Glycerin Standard, Water Glycerin Stock
mg/kg (final weight), g Solution, g
times, and performing a baseline correction.
50 100 5.0
7.6.8 Sample Digestion System—capable of heating, and
20 100 2.0
stirring with integrated reflux. Reflux is needed to minimize
10 100 1.0
loss of petroleum diesel in biodiesel blend samples.Achiller is 5 100 0.5
1 100 0.1
recommended for providing water to the reflux condenser for
0.5 100 0.05
efficiency and to conserve water resources.
7.7 Mechanical Wrist Shaker.
7.8 Gloves, nitrile.
9.1.1 Glycerin Stock Solution, 1000 mg/L—Accurately
8. Reagents and Materials
weigh 1 g of 99.5+ % glycerin to the nearest tenth of a
milligram (0.0001 g) and transfer to a 1 L volumetric flask.
8.1 Purity of Reagents—Reagent grade or higher purity
Dilute to the mark with water. Shake or swirl to mix the
chemicals shall be used for the preparation of all samples,
standard for homogeneity. Other volumes of stock solution
standards and eluent solutions. Unless otherwise indicated, it is
may be prepared using the appropriate ratio of reagents.
intended that all reagents conform to the specifications of the
Committee on Analytical Reagents of the American Chemical
9.2 Working Standards—Prepare glycerin working stan-
Society, where such specifications are available. Other grades
dards according to Table 1.
may be used, provided it is first ascertained that the reagent is
9.2.1 Alternatively, commercial stock calibration solutions
of sufficiently high purity to permit its use without lessening
can be used, provided that the solutions are traceable to
the accuracy of the determination.
primarystocksolutionsorcertifiedreferencematerials,andare
free from other analytes.
8.2 Water Quality—Unless otherwise indicated, reference to
water shall be understood to mean reagent water as defined by
10. Calibration
Type II in Specification D1193 or better. For eluent preparation
10.1 Set up the ion chromatograph according to the manu-
and handling, comply with all ion chromatograph instrument
facturer’s instructions. No specific parameters are given here
and column vendor requirements (for example, filtering,
since different manufacturer’s equipment might require
degassing, etc.).
changes in eluent, flow conditions, and instrument settings to
8.3 Eluent Stock Solution, sodium hydroxide (NaOH, 50 %
perform the separation and obtain the results. Calibrate the ion
certified, ACS).
chromatograph with at least five concentration levels of
8.3.1 Eluent Preparation, 0.10 M NaOH. Weigh 8.00 g 6
glycerin, starting near but above the minimum detection limit,
0.02 gof50 %NaOHinreagentwaterina1 Lvolumetricflask
and covering the expected working range of samples subse-
and dilute to volume with degassed reagent water. The eluent
quently to be analyzed. Select concentrations of calibrant
solution used may be different if other systems or analytical
solutions used that bracket the expected range for the samples
columns are used. Other volumes of stock solution may be
to be analyzed. Use one or more mid-range standards to verify
prepared using appropriate ratios of reagents. Ready to use
the linearity of the calibration plot.
reagents may be used. Consult with the instrument manufac-
10.1.1 Typical ion chromatographic conditions:
turer for guidance and use. Do not store sodium hydroxide
Flow: 1.0 mL⁄min
solutions in glass.
Sample loop: 10 µL
8.4 Potassium Hydroxide Solution for Total Glycerin, 1.0 M
Other analytical conditions may be used per the manufac-
KOH. Weigh out 56.1 g of ACS grade potassium hydroxide
turer’s instructions.
pellets. Dissolve the pellets in approximately 250 mLDI water
NOTE 1—The sample loop volume will vary based on the column
in a 1 L volumetric flask. Use caution when handling the flask
capacity, sensitivity, and other factors. Refer to ion chromatography
due to the heat produced during the dissolution of the potas-
equipment manuals and column information for instrument/column-
sium hydroxide. Dilute to the mark with DI water. Prepared
specific details.
ready to use 1.0 M potassium hydroxide solutions made with
10.1.2 Establish analytical curves with only one detector
acceptable purity materials may also be used. Keep containers
scale setting. This will prevent a change of slope affecting the
tightlyclosedwhennotinusetominimizecarbonateformation
analytical curve.
from atmospheric carbon dioxide.
10.2 Verify the analytical calibration plot daily or whenever
9. Preparation of Standard Solutions
samples are to be run, prior to the analysis of samples to verify
the system resolution, calibration, and sensitivity as part of the
9.1 Stock and working solutions.
quality verification process (see Section 14).
10.3 Repeat calibration after any change of the ion chroma-
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
tography eluent solution from 8.3, to reestablish ion retention
listed by the American Chemical Society, see Annual Standards for Laboratory
times and resolution. Use a check standard to verify
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
calibration, retention times, and resolution after any change in
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. the IC eluent solution from 8.3. Recalibrate if needed.
D7591−12 (2017)
FIG. 2Typical Glycerin Calibration Plot
10.4 Measurement of the Calibration Standards—Inject 11.1.5 After shaking the sample, let it settle until the oil and
10 µL of each calibration solution from 9.2 into the ion aqueous phases are separated.
chromatograph, and measure the areas of the peaks corre-
11.1.6 Set up the ion chromatograph in accordance with the
sponding to glycerin. Generally, one injection per sample is
manufacturer’s instructions.
sufficient. Refer to Section 14 for quality control discussion.
11.1.7 Equilibrate the system by pumping eluent for 15 min
10.5 Construct the glycerin calibration plots by plotting the
to 30 min or until a stable baseline is obtained.
peak areas against the glycerin concentrations. Use linear
11.1.8 Start the ion chromatographic run in accordance with
regression to determine the best straight-line calibration. A
the manufacturer’s instructions.
linear least squares correlation coefficient of 0.99 or greater is
11.1.9 Directly inject 10 µL of the aqueous extract into the
required (see Fig. 2). The response factor for glycerin, Rf, is
ion chromatograph, and measure the area of the peak corre-
the slope of the calibration plot straight line, in mg/kg/(area
sponding to glycerin.
count).
11.1.9.1 For most samples, a single injection is sufficient.
10.5.1 If the plot of the peak area values against the ion
However for every tenth sample, perform two injections and
concentrations is not linear (the correlation factor should be at
calculate the mean of the peak areas corresponding to glycerin.
least 0.99), the procedure should be checked for errors, and if
Thetwoareameasurementsshallbewithin20 %ofeachother.
necessary, the calibration should be repeated starting from
If the areas are different by more than 20 %, do not continue
Section 9.
running samples, until at least 20 % area repeatability can be
11. Procedure
achieved.
11.1.10 If the glycerin concentration exceeds that of the
11.1 For Free Glycerin in Biodiesel and its Blends:
highest calibration solution, dilute the sample solution with
11.1.1 Obtain samples in accordance with Practice D4057
waterasappropriate,andrepeatthesamplemeasurement.Take
or Practice D4177. Mix the samples thoroughly to ensure
homogeneity. A representative portion shall be taken for in
...