ASTM D6756-17

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Designation: D6756 − 10 (Reapproved 2015) D6756 − 17
Standard Test Method for
Determination of the Red Dye Concentration and Estimation
of the ASTM Color of Diesel Fuel and Heating Oil Using a
Portable Visible Spectrophotometer
This standard is issued under the fixed designation D6756; 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 Scope*
1.1 This test method covers the determination of the red dye concentration of diesel fuel and heating oil and the estimation of
the ASTM color of undyed and red-dyed diesel fuel and heating oil. The test method is appropriate for use with diesel fuel and
heating oil of Grades 1 and 2 described in Specifications D396, D975, D2880, and D3699. Red dye concentrations are determined
at levels equivalent to 0.1 mg ⁄L to 20 mg ⁄L of Solvent Red 26 in samples with ASTM colors ranging from 0.5 to 5. The ASTM
color of the base fuel of red-dyed samples with concentration levels equivalent to 0.1 mg ⁄L to 20 mg ⁄L of Solvent Red 26 is
estimated for the ASTM color range from 0.5 to 5. The ASTM color of undyed samples is estimated over the ASTM color range
of 0.5 to 5.
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.
2. Referenced Documents
2.1 ASTM Standards:
D396 Specification for Fuel Oils
D975 Specification for Diesel Fuel Oils
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D2880 Specification for Gas Turbine Fuel Oils
D3699 Specification for Kerosine
D4052 Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D6045 Test Method for Color of Petroleum Products by the Automatic Tristimulus Method
D6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport
to Measure the Same Property of a Material
E203 Test Method for Water Using Volumetric Karl Fischer Titration
E1655 Practices for Infrared Multivariate Quantitative Analysis
E2056 Practice for Qualifying Spectrometers and Spectrophotometers for Use in Multivariate Analyses, Calibrated Using
Surrogate Mixtures
3. Terminology
3.1 Definitions:
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
D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.
Current edition approved Oct. 1, 2015May 1, 2017. Published December 2015May 2017. Originally approved in 2002. Last previous edition approved in 20102015 as
D6756 – 10.D6756 – 10 (2015). DOI: 10.1520/D6756-10R15.10.1520/D6756-17.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6756 − 17
3.1.1 ASTM color, n—the name of an empirical scale of expressing the color of a petroleum liquid darker than Saybolt color
based on a scale of 0.5 (lightest) to 8 Dil (darkest) and determined by Test Method D1500.
3.1.2 surrogate calibration, n—a multivariate calibration that is developed using a calibration set which consists of mixtures
with pre-specified and reproducible compositions that contain substantially fewer chemical components than the samples which
will ultimately be analyzed. E2056
3.1.3 surrogate method, n—a standard test method that is based on a surrogate calibration. E2056
3.2 Definitions of Terms Specific to This Standard:
3.2.1 red dye, n—substance that, when added to fuel, absorbs green light and imparts a red color to the product. For this test
method, red dyes are:
3.2.1.1 product dyes, n—alkyl derivatives of azobenzene-4-azo-2-naphthol (methyl derivatives of Color Index No. 26105)
which are more soluble in diesel fuel.
3.2.1.2 solvent red 26, n—an azobenzene-4-azo-2-naphthol dye of a specific chemical structure that is used to gage the amount
of red dye present in a given sample.
4. Summary of Test Method
4.1 A sample is introduced into the liquid specimen cell. The cell is placed into the light path of the apparatus. A beam of visible
light is imaged through the sample onto a detector, and the detector response is determined. Wavelengths of the spectrum, which
correlate highly with the red dye concentration and the ASTM color, are selected for analysis using selective bandpass filters. A
multivariate mathematical model converts the absorption values from the filters to the red dye concentration and the estimated
ASTM color.
5. Significance and Use
5.1 In the United States, high sulfur content (defined by the United States Environmental Protection Agency (USEPA)) middle
distillate products and diesel fuel used for off-road purposes, other than aviation turbine fuel, are required by government agencies
to contain red dye. The dye concentration required to be present in high sulfur high-sulfur and off-road diesel products is regulated
by the United States Environmental Protection Agency and the United States Internal Revenue Service, respectively.
5.2 Some fuels that are readily exchanged in the market have a color specification. The color of the base fuel is masked by the
presence of the red dye. This test method provides a means of estimating the base color of Number 1 and Number 2 diesel fuel
and heating oil in the presence of red dye.
5.3 The test method provides a means to indicate conformance to contractual and legal requirements.
6. Interferences
6.1 The presence of colorants other than the hydrocarbons typical of Number 1 and 2 diesel fuel and heating oils, or the presence
of red dye other than the specified types, can interfere with the accurate determination of the red dye concentration reported as
Solvent Red 26 equivalent or the base fuel ASTM color.
7. Apparatus
7.1 Filter Spectrophotometer, is equipped with specimen chamber, visible wavelength source, four 10 nm 6 2 nm (full width
at half transmission maximum) bandpass wavelength discriminating filters having center wavelengths at 450 nm 6 2 nm, 520 nm
6 2 nm, 650 nm 6 2 nm, and 700 nm 6 2 nm. The bandpass filters are used in conjunction with the visible wavelength source
to produce light in the blue, green, red, and far-red regions of the electromagnetic spectrum. A detector converts the transmitted
3,4
light to an electronic signal that is processed by an A-D converter and a microprocessor.
7.2 Specimen Cell, constructed of polymethacrylate or clear optical glass having a path length of approximately 1 cm. If more
than one cell is used for calibration, qualification, and sample measurement, the path length of the cells must be matched to
60.001 cm.
8. Sampling
8.1 Samples shall be taken in accordance with Practice D4057 or D4177.
8.2 Precautions must be taken to shield the samples from light prior to analysis.
9. Calibration and Standardization of the Apparatus
9.1 The instrument is calibrated according to the procedure described in Annex A2.
NOTE 1—The DT100C instruments are calibrated at the factory by the vendor.
DT100C instruments used to develop this precision statement are available from PetroSpec, Inc., 530 Main St., Acton, MA 01720.
The sole source of supply of the apparatus known to the committee at this time is PetroSpec, Inc. If you are aware of alternative suppliers, please provide this information
to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.
D6756 − 17
9.2 The instrument is qualified according to the procedure described in Annex A3.
NOTE 2—The DT100C instruments are qualified at the factory by the vendor.
9.2.1 If the qualification procedure is performed by the vendor, then the user shall perform a quality control check according
to the procedure described in Section 10.
10. Quality Control Check
10.1 To confirm the performance of the instrument, periodically measure the red dye concentration and the ASTM color of three
control samples using the procedure outlined in Section 11. The quality control check standards should be analyzed at least once
a week or before the sample analysis if the instrument is used less frequently than weekly or if the instrument is moved to a
different laboratory or field location.
NOTE 3—Quality control samples are available from DT100CDT100C. .
10.1.1 A standard of known dye concentration and ASTM color is made according to the information in A1.4. The set of quality
control samples shall have a low, medium, and high red dye concentration (0 mg ⁄L to 14 mg ⁄L 6 2 mg ⁄L) and a low, medium,
and high ASTM color (0 to 5 ASTM color units).
10.1.2 The standards are stable for at least one year when stored in the dark in tightly sealed bottles.
10.2 If the red dye concentration determined for one of the quality control samples differs from the known value by more than
1.0 mg ⁄L or if the estimated ASTM color for one of the quality control samples differs from the known value by more than 0.5
units, then the measurement system is out-of-control and cannot be used to determine the red dye concentration or used to estimate
the ASTM color until the cause of the out-of-control behavior is corrected.
10.3 If correction of out-of-control behavior requires repair to the instrument or recalibration of the instrument, the qualification
of instrument performance described in Annex A3 shall be performed before the system is used to measure red dye concentration
or used to estimate ASTM color.
11. Procedure
11.1 Prepare the filter spectrophotometer for operation in accordance with the manufacturer’s instructions.
11.2 Equilibrate the sample to between 20 °C and 25 °C.
11.3 Without filtering the sample (see 13.6), fill a clean, dry specimen cell. The external optical surfaces shall be clean. If not,
wipe clean and dry with a piece of lint-free paper (for example, lens paper).
11.4 Insert the specimen cell into the cell chamber of the instrument.
11.5 Record the Solvent Red 26 equivalent concentration and the estimated ASTM color.
12. Report
12.1 Report the red dye concentration to the nearest 0.1 mg ⁄L as Solvent Red 26 equivalent dye.
NOTE 4—The number of milligrams per litre of Solvent Red 26 equivalents measured by the DT100C instrument is labeled as ppm on the display. The
ppm unit reported by the DT100C instrument is equivalent to mg/L.
12.2 Report the estimated ASTM color value as: estimated ASTM color using ASTM D6756. Report the result to the nearest 0.1
color value.
12.2.1 The reported estimated ASTM color value can be converted to a value that mimics the reporting convention of the Test
Method D1500. For estimated ASTM color values that are x.0 or x.5, the estimated value is reported unchanged. For estimated
color values between x.1 and x.4, round up the value to the nearest x.5 and place an L before the result. For estimated color values
between x.6 and x.9, round up the value to the nearest whole number and place an L before the result. If the estimated color value
is greater than 8.0, report the estimated result as >8.
13. Precision and Bias
13.1 Interlaboratory tests of the procedure were carried out using sixteen samples covering the red dye concentration range
equivalent to 0 mg ⁄L to 16 mg ⁄L of Solvent Red 26 equivalents and covering the range of ASTM color from 0.5 to 3.0. Seven
laboratories participated in the interlaboratory tests. The precision of this procedure as determined by the statistical examination
of the interlaboratory test results is as follows:
13.1.1 Repeatability—The difference between successive test results obtained with the same apparatus under constant operating
conditions on identical samples would in the long run, in normal and correct operation of the test method, exceed the following
value in only one case in twenty:
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1521. Contact ASTM Customer
Service at service@astm.org.
D6756 − 17
r 5 0.22 mg/L
for Solvent Red 26 equivalent dye concentrations between 0.1 mg ⁄L and 20.0 mg ⁄L, and
r 50.085 ASTM color units
for samples in the ASTM color range of 0 to 5.
13.1.2 Reproducibility—The difference between two single and independent results obtained from different instruments on
identical samples, would in the long run, in normal and correct operation of the test method, exceed the following value in only
one case in twenty:
R 5 0.86 mg/L
for Solvent Red 26 equivalent dye concentrations between 0.1 mg ⁄L and 20.0 mg ⁄L, and
R 50.20 ASTM color units
for samples in the ASTM color range of 0 to 5.
13.2 Bias—Since there is no accepted reference material suitable for determining the bias for the procedure in this test method,
bias has not been determined.
13.3 Relative Bias (Dye Concentration)—Some relative bias, among certain samples, was observed when the Solvent Red 26
concentration results were compared to the expected Solvent Red 26 concentrations. The bias between the theoretical and measured
Solvent Red 26 concentration is observed with the test samples that were made using Solvent Red 164, the chemical used to
commercially dye diesel fuel. The observed bias does appear to be of a systematic nature and is not known to be related to the
accuracy of this test method, since the Solvent Red 26 equivalency of the Solvent Red 164 used in sample preparation has not been
determined, only estimated.
13.4 Relative Bias (ASTM Color)—Relative bias, for one sample, was observed when the color results were compared to the
Test Method D1500 results; however, this bias is near the reproducibility of the test methods and is inconclusive. The overall
relative bias to Test Method D1500 is not significant.
NOTE 5—The average bias of the estimated ASTM color relative to Test Method D1500 was −0.17. The largest average biases, −0.4 to −0.5, were
observed for four samples that had an ASTM color of 0.5 and red dye concentrations that ranged from 10 mg ⁄L to 20 mg ⁄L.
13.5 Relative Bias (Unfiltered vs.versus Filtered Samples)—A single laboratory analyzed a total of 99 separate split samples
(unfiltered versus filtered) to determine the impact that filtering samples can have on reported red dye concentration results. Based
on a Practice D6708 analysis of the results, where the Y-method was unfiltered samples and the X-method was filtered samples,
a bias correction formula of Y = X – 0.107 was determined. In short, filtering the samples led to a statistically significant bias being
determined. As such, to ensure testing consistency between laboratories, samples are not to be filtered as indicated in 11.3.
Inclusion of the Test Method D1500 analysis formula is for information only and not intended to be used by laboratories as an
official offset to apply to their data if samples were filtered.
13.6 The precision statements in 13.1 were derived from the 1997 interlaboratory test program. Participants analyzed 4four sets
of undyed base fuels and 12twelve sets of dyed base fuel/color combinations in duplicate in the ASTM color range of 0.5 to 3.0
and Solvent Red 26 equivalent dye concentration from 0 mg ⁄L to 16 mg ⁄L. Seven laboratories participated with the automatic filter
apparatus and six laboratories participated with the manual Test Method D1500 apparatus. Information on the types of samples and
their dye concentrations and colors are in the research report available at ASTM International Headquarters. Request ASTM RR:
RR:D02-1521.
14. Keywords
14.1 ASTM color; diesel fuel, heating oil; red dye concentration; visible spectrophotometry
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ANNEXES
(Mandatory Information)
A1. PROCEDURE FOR PREPARATION OF RED DYE/ASTM COLOR STANDARDS, QUALIFICATION SAMPLES, AND
QUALITY CONTROL SAMPLES
A1.1 Scope
A1.1.1 This annex is a description of the preparation of dye concentration and color standard samples used for calibration and
qualification. It also describes the preparation of possible standard samples that can be used for periodic checks.
A1.2 Apparatus
A1.2.1 Spectrophotometer, equipped to measure the absorbance of solutions in the spectral region from 380 nm to 780 nm with
an effective spectral slit width of 10 nm 6 2 nm or 5 nm 6 1 nm. Wavelength measurements shall be repeatable and known to be
accurate to 0.1 nm. The photometric linearity is to be 60.5 % of full scale and a photometric reproducibility of 60.2 %.
A1.2.2 Filter Spectrophotometer, see 7.1.
A1.2.3 Sample Cells, see 7.2.
A1.2.4 Balance, with a readability of 0.1 mg or better.
A1.2.5 Pipettes, 0.5 mL, 1 mL, and 2 mL capacity, Class A.
A1.2.6 Volumetric Flasks, 100 mL, 200 mL, and 250 mL capacity, Class A.
A1.2.7 Beaker, 50 mL capacity.
A1.3 Reagents
A1.3.1 Dyes:
A1.3.1.1 3-Methyl-1-(phenyl azo)-pyrazol-5-ol, (Yellow 5GS-EX), CAS registry number 4314-14-1.
A1.3.1.2 1-(phenyl azo)-2-naphthalenol, (Orange EX), CAS registry number 842-07-9.
A1.3.1.3 1,4 bis (butylamino)-9,10-anthracenedione, (Blue SB), CAS registry number 17354-14-2.
A1.3.1.4 1-[[(4-[dimethylphenyl)azo]dimethylphenyl]azo]-2-naphthalenol, (Red 5B-SP), CAS registry 1320-06-5.
A1.3.1.5 1,5 (or 1,8)-bis[(4-methylphenyl)amino]-9,10-anthracenedione, (Violet 3R), CAS registry number 8005-40-1.
A1.3.1.6 1-hydroxy-4-[(4-methylphenyl)amino]-9,10-anthracenedione, (Violet B-2R), CAS registry number 81-48-1.
A1.3.1.7 1,4-bis[(4-butylphenyl)amino]-5,8-dihydroxy-9,10-anthracenedione, (Green SG), CAS registry number 28198-05-2.
A1.3.1.8 1-[[2,5-dimethyl-4[(2-methylphenyl)azo]phenyl]azo]-2-naphthol, (Solvent Red 26), CAS registry number 4477-79-6.
A1.3.2 1,1-bis(3,4-dimethylphenyl)ethane, 90 % minimum purity, CAS registry number 1742-14-9.
A1.3.3 Dodecane, anhydrous, 99 % minimum purity, CAS registry number 112-40-3.
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A1.3.4 Xylenes- isomers plus ethylbenzene,A.C.S. reagent grade, CAS registry number 1330-20-7.
A1.4 Preparation Procedure for the ASTM Standard Samples
A1.4.1 Measure 0.2500 g 6 0.0005 g of Yellow 5GS-EX into a 50 mL beaker and dissolve the dye in 20 mL of 1,1-bis(3,4-
dimethylphenyl)ethane. Quantitatively transfer the Yellow 5GS-EX solution to a 250 mL volumetric flask, dilute to the mark with
1,1-bis(3,4-dimethylphenyl)ethane and mix well. This solution is called the Yellow 5GS-EX dye solution.
A1.4.2 Repeat the above procedure for the Orange EX, Blue SB, Red 5B-SP, Violet 3R, Violet B-2RB-2R, and Green SG. These
solutions are called Orange EX dye solution, the Blue SB dye solution, the Red 5B-SP dye solution, the Violet 3R dye solution,
the Violet B-2R dye solution, and the Green SG dye solution, respectively.
A1.4.3 Pipette 2 mL of the Yellow 5GS-EX solution into a 200 mL volumetric flask, dilute to the mark with dodecane, and mix
well. Using separate flasks, repeat this procedure with the Orange EX dye solution, t
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