ASTM D7821-12(2018)

Standard Test Method for Field Test Determination of Urea Concentration in Diesel Exhaust Fluid (DEF)

SCOPE
1.1 This test method covers a technique for field testing the concentration of aqueous urea-based diesel exhaust fluid (DEF) prescribed for use in diesel engines equipped with selective catalytic reduction technology and is not intended to circumvent or replace the more accurate determination of urea content by refractive index laboratory method, described in ISO 22241-2, Annex C.  
1.2 This test method is designed solely as a quantitative test to determine the concentration of urea in DEF and does not purport to determine the quality of DEF nor to detect trace or other contaminants therein. Biuret content of DEF creates a known bias in this test method. See section 9.2.1 for details.  
1.3 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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: 31-Aug-2018
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D15 - Engine Coolants and Related Fluids
• Drafting Committee: D15.25 - Diesel Exhaust Fluid

Relations

• Replaces: ASTM D7821-12 - Standard Test Method for Field Test Determination of Urea Concentration in Diesel Exhaust Fluid (DEF)
• Effective Date: 01-Sep-2018

Overview

ASTM D7821-12(2018) provides a standard test method for field determination of the urea concentration in diesel exhaust fluid (DEF). DEF, an aqueous urea solution, is essential for selective catalytic reduction (SCR) systems in diesel engines to reduce nitrogen oxide (NOx) emissions. This test method enables rapid, quantitative urea concentration evaluation in DEF using a digital refractometer, making it valuable for field applications where speed and practicality are critical.

This method is intended as a quick field test and supports, but does not replace, the more precise laboratory determination of urea by refractive index according to ISO 22241-2, Annex C. The standard focuses only on the quantification of urea and does not assess DEF purity or detect additional contaminants.

Key Topics

• Field Test for Urea in DEF: Outlines a digital refractometry approach designed for quick analysis of urea concentration in DEF on-site.
• Diesel Exhaust Fluid (DEF): Defines DEF as an aqueous solution of technically pure urea in high purity water, commonly at 32.5% by weight.
• Selective Catalytic Reduction (SCR): Highlights the use of DEF in SCR-equipped diesel engines, which are critical for meeting stringent emission regulations.
• Use of Digital Refractometer: Specifies instrument features, including unit of measure (urea percent by weight), precision, reference temperature (20°C), automatic temperature compensation, and digital display.
• Sample Handling: Emphasizes the importance of cleanliness in sampling and testing to avoid contamination and ensure accurate readings.
• Calibration Requirements: Details the need to zero set the refractometer with distilled water and equilibrate temperatures for reliable results.
• Limitations and Bias: Notes that biuret impurities, up to 0.3% m/m as permitted by ISO 22241, can influence test bias, and the method does not detect DEF contaminants.

Applications

The ASTM D7821-12(2018) test method is widely used in the following contexts:

• Field Quality Control: Enables service centers, fleet operators, and transportation companies to verify DEF concentration quickly, helping prevent SCR system malfunctions or emissions noncompliance due to off-spec DEF.
• DEF Production and Distribution: Supports producers and distributors in spot-checking product during filling, transfer, or at customer locations.
• Vehicle Maintenance: Service technicians use this method to assess DEF quality at maintenance intervals, before repairs, or following DEF tank refills.
• Environmental and Regulatory Compliance: Assists stakeholders in the supply chain in meeting legislative requirements for vehicle emissions and DEF quality especially during spot audits and roadside inspections.
• Equipment and Instrument Validation: Used to calibrate and validate refractometers dedicated to DEF analysis.

Related Standards

Understanding the broader context of DEF testing and quality assurance is enhanced through related standards:

• ISO 22241 Series: International standards detailing specifications and testing methods for AUS 32 (DEF), including requirements for composition, quality, handling, and laboratory urea concentration testing.
• ASTM D7546: Test method for optical determination of urea concentration in DEF by refractive index in laboratory settings.
• API Diesel Exhaust Fluid Certification: A program that and marks DEF products compliant with ISO 22241, ensuring quality and traceability.

By complying with ASTM D7821-12(2018), organizations in the automotive and emissions control sectors can maintain DEF quality assurance and support optimal SCR system function, contributing to effective NOx emissions reduction and regulatory adherence.

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: D7821 − 12 (Reapproved 2018)
Standard Test Method for
Field Test Determination of Urea Concentration in Diesel
Exhaust Fluid (DEF)
This standard is issued under the fixed designation D7821; 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 3. Terminology
1.1 This test method covers a technique for field testing the 3.1 Definitions of Terms Specific to This Standard:
concentrationofaqueousurea-baseddieselexhaustfluid(DEF) 3.1.1 American Petroleum Institute (API), n—a nonprofit
prescribed for use in diesel engines equipped with selective trade association that licenses diesel exhaust fluid (DEF)
catalytic reduction technology and is not intended to circum- marketers to use the API Diesel Exhaust Fluid Certification
ventorreplacethemoreaccuratedeterminationofureacontent Mark. A marketer may be licensed to use the API Mark if its
by refractive index laboratory method, described in ISO DEF is in compliance with the most recent and applicable
22241-2, Annex C. edition of ISO 22241.
3.1.2 diesel exhaust fluid, DEF, n—preparation of aqueous
1.2 This test method is designed solely as a quantitative test
urea [(NH ) CO], containing 32.5 % by weight of technically
to determine the concentration of urea in DEF and does not
2 2
pure urea in high-purity water with quality characteristics
purport to determine the quality of DEF nor to detect trace or
defined by ISO 22241.
other contaminants therein. Biuret content of DEF creates a
known bias in this test method. See section 9.2.1 for details.
3.1.3 refractive index, n—fundamental physical property of
a substance that is related to the ratio of the velocity of light in
1.3 Units—The values stated in SI units are to be regarded
air, to its velocity in the substance under examination, at a
as the standard. No other units of measurement are included in
specified temperature and wavelength.
this standard.
3.1.4 refractometer, n—optical instrument that measures the
1.4 This standard does not purport to address all of the
refractive index of a substance and can be used to characterize
safety concerns, if any, associated with its use. It is the
the concentration or mixture ratio of various substances.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.1.5 biuret, n—chemical compound which appears as a
mine the applicability of regulatory limitations prior to use.
characteristic impurity in aqueous urea solutions.
1.5 This international standard was developed in accor-
3.1.6 AUS 32, n—ISO designation for DEF also known as
dance with internationally recognized principles on standard-
NOx reduction agent AUS 32 (aqueous urea solution).
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 A digital refractometer with a special scale specific to
Barriers to Trade (TBT) Committee.
the percent by weight of urea is used to measure the concen-
tration of a DEF sample.
2. Referenced Documents
4.2 TodetermineDEFconcentration,therefractometershall
2.1 ISO Standard:
first be zero set to distilled water. Next, a sample of DEF is
ISO 22241 Diesel engines—NOx reduction agent AUS 32
placed on the measuring surface of the refractometer and the
temperature of the instrument, fluid, and ambient environment
is allowed to equilibrate. A reading is taken by pressing a
This test method is under the jurisdiction ofASTM Committee D15 on Engine
button, and the unit of measure and concentration are directly
Coolants and Related Fluids and is the direct responsibility of Subcommittee
D15.25 on Diesel Exhaust Fluid.
read from a digital display.
Current edition approved Sept. 1, 2018. Published September 2018. Originally
approved in 2012. Last previous edition approved in 2012 as D7821–12. DOI:
10.1520/D7821–12R18. Sources for DEF refractometers used to establish the precision and bias of this
Available from American National Standards Institute (ANSI), 25 W. 43rd St., method: MISCO Refractometer, 6275 Cochran Road, Solon, OH 44139, and
4th Floor, New York, NY 10036, http://www.ansi.org. Reichert Technologies, 3362 Walden Avenue, Suite 100, Depew, NY 14043.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7821 − 12 (2018)
5. Apparatus originalsamplecontainer.Thesamplecontainershouldonlybe
opened long enough to remove a sample and should be
5.1 Refractometer—Arefractometer is an optical instrument
immediately sealed.
used to measure the physical properties of a solution. Refrac-
7.1.3 A clean disposable plastic pipette should be used to
tometers suitable for use in this test method shall possess the
transfer a sample to the refractometer and the pipette then
following characteristics:
immediately discarded.
5.1.1 Unit of Measure—The unit of measure for all DEF
readings shall be urea percent by weight and this shall be
7.2 Measuring the Sample:
clearly identified on the refractometer.
7.2.1 The refractometer and ambient environment should be
5.1.2 Range—The refractometer shall have a minimum
between 10 to 45 °C.
measuring range of 0.0 to 37.0 percent by weight.
7.2.2 Inspect the refractometer measuring surface to insure
5.1.3 Resolution—The refractometer shall resolve readings
that it is free of residue from a previous test. Clean the sample
to 0.1 % urea by weight.
surface and sample well with distilled water and tissue if
5.1.4 Precision and Bias—The refractometer must be ca-
needed.
pable of reading with a
...