ASTM D7328-23

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Designation: D7328 − 22 D7328 − 23
Standard Test Method for
Determination of Existent and Potential Inorganic Sulfate
and Total Inorganic Chloride in Fuel Ethanol by Ion
Chromatography Using Aqueous Sample Injection
This standard is issued under the fixed designation D7328; 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*
1.1 This test method covers an ion chromatographic procedure for the determination of the existent inorganic and potential sulfate
and total inorganic chloride content in hydrous and anhydrous denatured ethanol to be used in motor fuel applications. It is intended
for the analysis of ethanol samples containing between 0.55 mg ⁄kg and 20 mg ⁄kg of existent inorganic sulfate, 4.0 mg ⁄kg to
20 mg ⁄kg of potential inorganic sulfate, and 0.75 mg ⁄kg to 50 mg ⁄kg of total inorganic chloride.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards
prior to usage
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:
D1193 Specification for Reagent Water
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
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D5827 Test Method for Analysis of Engine Coolant for Chloride and Other Anions by Ion Chromatography
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
D6792 Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
D7318 Test Method for Existent Inorganic Sulfate in Ethanol by Potentiometric Titration
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
D02.03 on Elemental Analysis.
Current edition approved Oct. 1, 2022March 1, 2023. Published October 2022April 2023. Originally approved in 2007. Last previous edition approved in 20172022 as
D7328 – 17. DOI: 10.1520/D7328- 22.22. DOI: 10.1520/D7328- 23.
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
D7328 − 23
D7319 Test Method for Determination of Existent and Potential Sulfate and Inorganic Chloride in Fuel Ethanol and Butanol by
Direct Injection Suppressed Ion Chromatography
2.2 Other Standard:
ISO/CEN15492 Ethanol as a Blending Component for Petrol—Determination of Inorganic Chloride—Ion Chromatographic
Method
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 existent inorganic sulfate, n—inorganic sulfate species actually present in the sample at the time of analysis with no oxidation
treatment.
3.2.2 inorganic chloride, n—chloride present as hydrochloric acid, ionic salts of this acid, or mixtures of these.
3.2.3 inorganic sulfate, n—sulfate species present as sulfuric acid, ionic salts of this acid, or mixtures of these.
3.2.4 potential sulfate, n—total inorganic sulfate species present after the sample has been reacted with an oxidizing agent.
4. Summary of Test Method
4.1 For existent inorganic sulfate and chloride, a small volume of a sample is evaporated to dryness and reconstituted to the initial
sample volume with deionized water, and injected into an ion chromatograph consisting of appropriate ion exchange columns,
suppressor and a conductivity detector. For potential sulfate, a small volume of a sample is evaporated to dryness and reconstituted
to the initial sample volume with 0.90 % hydrogen peroxide solution in water, and injected into an ion chromatograph. Ions are
separated based on their affinity for exchange sites of the resin with respect to the resin’s affinity for the eluent. The suppressor
increases the sensitivity of the method by both increasing the conductivity of the analytes and decreasing the conductivity of the
eluent. The suppressor converts the eluent and the analytes to the corresponding hydrogen form acids. Anions in the aqueous
sample are quantified by integration of their responses compared with an external calibration curve, calculated as mg/L for each
ion. The calibration standards are prepared from suitable salts dissolved in water solutions. Existent or potential inorganic sulfate
and chloride concentrations may be calculated as mg/kg by measuring the density of the original sample.
4.2 Similar methods for chloride and sulfate determinations can be found in Test Method D5827 for engine coolant, and for
ethanol in ISO/CEN15492, Test Method D7319 by ion chromatography with direct sample injection, and for sulfate only in Test
Method D7318 by potentiometric lead titration.
5. Significance and Use
5.1 Sulfates and chlorides may be found in filter plugging deposits and fuel injector deposits. The acceptability for use of the fuel
components and the finished fuels depends on the sulfate and chloride content.
5.2 Existent and potential inorganic sulfate and total chloride content, as measured by this test method, can be used as one measure
of the acceptability of gasoline components for automotive spark-ignition engine fuel use.
6. Interferences
6.1 Interferences can be caused by substances with similar ion chromatographic retention times, especially if they are in high
concentration compared to the analyte of interest. Sample dilution or standard addition can be used to minimize or resolve most
interference problems.
6.2 A water dip (system void, negative peak as shown in Fig. 1) may cause interference with some integrators. Usually, for
chloride and sulfate determinations, the water dip should not be a problem since the chloride and sulfate peaks are far enough away
from the water dip.
Available from International Organization for Standardization (ISO), 1 rue de Varembé, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
D7328 − 23
FIG. 1 Typical Ion Chromatogram of a Solution Containing 1 mg/kg of Various Anions in Water
6.3 Given the trace amounts of chloride and sulfate determined by this method, interferences can be caused by contamination of
glassware, eluents, reagents, etc. Great care must be taken to ensure that contamination is kept at the lowest possible levels. The
use of powder-free gloves is highly recommended to prevent sample contamination.
7. Apparatus
7.1 Analytical Balance, at least 2000 g capacity, capable of weighing accurately to 0.01 g.
7.1.1 Analytical Balance, at least 100 g capacity, capable of weighing accurately to 0.0001 g.
7.2 Drying Oven, controlled at 110 °C 6 5 °C for drying sodium sulfate and sodium chloride.
7.3 Desiccator, containing freshly activated silica gel (or equivalent desiccant) with moisture content indicator.
7.4 Pipettes or Volumetric Transferring Devices, Class A glass pipettes or their equivalent of 2.0 cc capacity or automatic pipettes
fitted with disposable polypropylene tips.
7.4.1 Plastic Syringe, 10 cc disposable, optionally fitted with a 0.2 μm syringe filter (must be chloride and sulfate-free).
7.5 Volumetric Flask, Class A of 1 L capacity and Class A of 10 mL capacity.
7.6 Ion Chromatograph, Analytical system with all required accessories including syringes, columns, suppressor, gases, and
detector.
7.6.1 Injection System, capable of delivering 25 μL with a precision better than 1 %.
7.6.2 Pumping System, capable of delivering mobile phase flows between 0.5 mL ⁄min and 1.5 mL ⁄min with a precision better than
5 %.
7.6.3 Guard Column, for protection of the analytical column from strongly retained constituents. Better separations are obtained
with greater separating power.
7.6.4 Anion Separator Column, capable of producing satisfactory analyte separation (see Fig. 1).
D7328 − 23
7.6.5 Anion Suppressor Device, micro membrane suppressor or equivalent. A cation exchange column in the hydrogen form has
been used successfully, but it will periodically need to be regenerated as required. This is indicated by a high background
conductivity and low analyte response.
7.6.6 Conductivity Detector, low volume (<2 μL) and flow, temperature compensated, capable of at least 0 μS ⁄cm to 1000 μS ⁄cm
on a linear scale.
7.6.7 Integrator or Chromatography Data System Software, capable of measuring peak areas and retention times, and correcting
the data according to the baseline of the chromatogram.
7.7 Gloves, powder-free examination type.
7.8 Hot Block, aluminum, capable of being heated to 65 °C with suitable holes to hold 15 mL glass vials, with a method of flowing
nitrogen over inserted samples.
7.9 Glass Vials, 15 mL with screw top.
8. Reagents
8.1 Purity of Reagents—Reagent grade or higher purity chemicals shall be used for the preparation of all samples, standards,
eluents, and regenerator solutions. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the
Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may
be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy
of the determination.
8.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water as defined by Type
I in Specification D1193. For eluent preparation and handling, comply with all ion chromatograph instrument and column vendor
requirements (for example, filtering, degassing, etc.).
8.3 Eluent Buffer Solution—The eluent solution used depends on the systems or analytical columns that are used (contact
instrument and column vendors). For the chromatograms in Fig. 1, the following eluent buffer was used: Sodium bicarbonate
(NaHCO ) 1.7 mM and sodium carbonate (Na CO ) 1.8 mM. Dissolve 2.8563 g 6 0.0005 g of NaHCO and 3.8157 g 6 0.0005 g
3 2 3 3
of Na CO in reagent water in a 1 L Type A volumetric flask and dilute to volume. Dilute 100 mL of this concentrate to 2000 mL
2 3
with reagent water for the final working eluent solution. Other volumes of stock solution may be prepared using appropriate ratios
of reagents. Follow the specific guidelines for this solution from the vendor of the column being used. Alternatively, this solution
can be purchased from a qualified vendor.
8.4 Suppressor Solution for Membrane Suppressor, 0.025 N sulfuric acid. Carefully add 13.7 mL of reagent grade sulfuric acid
(relative density 1.84) to approximately 500 mL reagent water in a 1 L volumetric flask. (Warning—This will generate a very hot
solution. Allow it to cool before diluting to 1000 mL volume. Never add water to concentrated acid!) Dilute to 1000 mL with
reagent water, and label this solution as 0.50 N sulfuric acid. Dilute 100 mL of this concentrate to 2000 mL with reagent water for
the final working suppressor solution. Other volumes of stock solution may be prepared using appropriate ratios of reagents.
Follow the specific guidelines for this solution from the vendor of the column being used.
8.5 Sodium Sulfate, anhydrous, reagent grade, 99 % minimum purity. (Warning—Do not ingest; avoid unnecessary exposure.)
8.6 Sodium Chloride, ACS reagent grade, 99 % minimum purity.
8.7 Ethanol, denatured with methanol, formula 3A or histological grade ethanol, anhydrous, denatured with ethyl acetate,
methylisobutyl ketone and hydrocarbon naphtha. (Warning—Flammable; toxic; may be harmful or fatal if ingested or inhaled;
avoid skin contact.)
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D7328 − 23
TABLE 1 Volumetric Preparation of Chloride and Sulfate
Standards in Type II Water
Chloride and
Chloride Stock Sulfate Stock
Sulfate Standards
Solution Solution
mg Chloride and
mL mL
Sulfate (each)/L water
-
50 Cl only 25 . . .
20 10 10
10 5 5
5 2.5 2.5
1 0.5 0.5
0.5 0.25 0.25
0.3 0.15 0.15
8.8 Hydrogen Peroxide Solution, 30 %, commercially available 30 % hydrogen peroxide solution.
8.9 Nitrogen Gas, 99.99 mol % pure, free of hydrocarbons.
9. Preparation of Standard Solutions
9.1 Stock Solutions:
9.1.1 Sulfate Stock Solution, approximately 2000 mg ⁄L—To ensure dryness, place anhydrous sodium sulfate (5 g) in a drying oven
at 110 °C for at least an hour, cool and store in a desiccator. Accurately weigh 2.96 g anhydrous sodium sulfate to the nearest tenth
of a milligram and transfer to a 1 L volumetric flask. Add Type III water to dissolve the sodium sulfate and make to volume.
Calculate the concentration of sulfate in the solution according to Eq 1. Other volumes of stock solution may be prepared using
the appropriate ratio of reagents.
stock sulfate mg/L 5 g Na SO 0.6764 1000 mg/g /1 L (1)
~ ! ~ ! ~ ! ~ !
2 4
where:
g Na SO = weight in grams of Na SO dissolved in 1 L, and
2 4 2 4
0.6764 = weight percent sulfate in Na SO .
2 4
9.1.2 Chloride Stock Solution, approximately 2000 mg ⁄L—To ensure dryness, place sodium chloride (5 g) in a drying oven at
110 °C for at least an hour, cool and store in a desiccator. Accurately weigh 3.30 g dried sodium chloride to the nearest tenth of
a milligram and transfer to a 1 L volumetric flask. Add Type III water to dissolve the sodium chloride and make to volume.
Calculate the concentration of chloride in the solution according to Eq 2. Other volumes of stock solution may be prepared using
the appropriate ratio of reagents.
stock chloride mg/L 5 g NaCl 0.6068 1000 mg/g /1 L (2)
~ ! ~ ! ~ ! ~ !
where:
g NaCl = weight in grams of NaCl dissolved in 1 L, and
0.6068 = weight percent chloride in NaCl.
9.2 Chloride and Sulfate Standards in Water—Type III water and sulfate and chloride stock solutions are added to a 1 L glass
volumetric flask according to Table 1 to achieve the desired standard. These standard solutions should be discarded and remade
every month.
9.2.1 Chloride and sulfate stock solutions from 9.1 are added quantitatively into the flask, mixed quantitatively with Type III water
according to Table 1. Be very careful to measure the exact volumes of the sulfate and chloride stock solutions that are added to
the flask, and to fill the flask to 1.00 L with Type III water. The sulfate and chloride concentrations of each standard are calculated
according to Eq 3(a) and Eq 3(b).
sulfate in standard mg/L 5 Va ×Ca/V a (3)
~ ! ~ !
chloride in standard mg/L 5 Vb ×Cb/V b
~ ! ~ !
D7328 − 23
where:
Va = volume of sulfate stock solution (for example, Table 1, Column 3), in mL,
Ca = concentration of sulfate stock (Eq 1), in mg/L,
Vb = volume of chloride stock solution (for example, Table 1, Column 2), in mL,
Cb = concentration of chloride stock (Eq 2), in mg/L, and
V = final volume of standard solution, in L.
9.2.2 Multiples or fractions of Table 1 values can be used to prepare different total volumes (V) of standards, using Eq 3(a) and
Eq 3(b) to calculate standard ion concentrations.
NOTE 1—Alternatively, commercially available stock calibration solutions can be used, provided that the solutions are traceable to primary stock solutions
or certified reference materials, and are free from other analytes.
9.3 Hydrogen Peroxide Solution, 0.90 %—Carefully pipette 3.0 mL of the 30 % hydrogen peroxide reagent into a 100 mL
volumetric. Add Type III water to make to volume.
NOTE 2—Hydrogen peroxide will degrade in aqueous solution, therefore prepare fresh 0.90 % solution daily.
10. Calibration
10.1 Set up the ion chromatograph according to the manufacturer’s instructions. No specific parameters
...