ASTM D7328-07

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An American National Standard
Designation:D7328–07
Standard Test Method for
Determination of Total 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 D 7328; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 6792 Guide for Quality System in Petroleum Products
and Lubricants Testing Laboratories
1.1 This test method covers an ion chromatographic proce-
2.2 Other Standard:
dure for the determination of the total and potential inorganic
ISO/CEN15492 Ethanol as a Blending Component for
sulfate and total inorganic chloride content in hydrous and
Petrol – Determination of Inorganic Chloride – Ion
anhydrous denatured ethanol to be used in motor fuel applica-
Chromatographic Method
tions. It is intended for the analysis of ethanol samples
containing between 0.55 and 20 mg/kg of total inorganic
3. Terminology
sulfate, 4.0 to 20 mg/kg of potential inorganic sulfate, and 0.75
3.1 Definitions of Terms Specific to This Standard:
to 50 mg/kg of total inorganic chloride.
3.1.1 inorganic chloride, n—chloride present as hydrochlo-
1.2 The values stated in SI units are to be regarded as
ric acid, ionic salts of this acid, or mixtures of these.
standard. No other units of measurement are included in this
3.1.2 inorganic sulfate, n—sulfate species present as sulfu-
standard.
ric acid, ionic salts of this acid, or mixtures of these.
1.3 This standard does not purport to address all of the
3.1.3 potential sulfate, n—total sulfur species present in the
safety concerns, if any, associated with its use. It is the
samplethatcanbeoxidizedtoinorganicsulfateinthepresence
responsibility of the user of this standard to establish appro-
of an oxidizing agent.
priate safety and health practices and determine the applica-
3.1.4 total sulfate, n—inorganic sulfate species actually
bility of regulatory limitations prior to use. Material Safety
present in the sample at the time of analysis with no oxidation
Data Sheets are available for reagents and materials. Review
treatment.
them for hazards prior to usage.
4. Summary of Test Method
2. Referenced Documents
2 4.1 For total inorganic sulfate and chloride, a small volume
2.1 ASTM Standards:
of a sample is evaporated to dryness and reconstituted to the
D 1193 Specification for Reagent Water
initial sample volume with deionized water, and injected into
D 4052 Test Method for Density and Relative Density of
an ion chromatograph consisting of appropriate ion exchange
Liquids by Digital Density Meter
columns, suppressor and a conductivity detector. For potential
D 4057 Practice for Manual Sampling of Petroleum and
sulfate, a small volume of a sample is evaporated to dryness
Petroleum Products
and reconstituted to the initial sample volume with 0.90 %
D 4177 Practice for Automatic Sampling of Petroleum and
hydrogen peroxide solution in water, and injected into an ion
Petroleum Products
chromatograph. Ions are separated based on their affinity for
D 5827 Test Method for Analysis of Engine Coolant for
exchangesitesoftheresinwithrespecttotheresin’saffinityfor
Chloride and Other Anions by Ion Chromatography
the eluent. The suppressor increases the sensitivity of the
D 6299 Practice for Applying Statistical Quality Assurance
method by both increasing the conductivity of the analytes and
Techniques to Evaluate Analytical Measurement System
decreasing the conductivity of the eluent. The suppressor
Performance
converts the eluent and the analytes to the corresponding
hydrogen form acids. Anions in the aqueous sample are
This test method is under the jurisdiction of ASTM Committee D02 on
quantified by integration of their responses compared with an
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
externalcalibrationcurve,calculatedasmg/Lforeachion.The
D02.03 on Elemental Analysis.
Current edition approved Jan. 1, 2007. Published February 2007.
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 Available from International Organization for Standardization (ISO), 1 rue de
the ASTM website. Varembé, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7328–07
FIG. 1 Typical Ion Chromatogram of a Solution Containing 1 mg/kg of Various Anions in Water
calibration standards are prepared from suitable salts dissolved levels. The use of powder-free gloves is highly recommended
in water solutions. Total or potential sulfate and chloride to prevent sample contamination.
concentrations may be calculated as mg/kg by measuring the
density of the original sample.
7. Apparatus
4.2 Similar methods for chloride and sulfate determinations
7.1 Analytical Balance, at least 2000 g capacity, capable of
can be found inTest Method D 5827 for engine coolant and for
weighing accurately to 0.01 g.
ethanol in ISO/CEN15492. Subcommittee D02.03 is develop-
7.1.1 Analytical Balance, at least 100 g capacity, capable of
ing new standards that address direct injection suppressed ion
weighing accurately to 0.0001 g.
chromatography and, for sulfate only, by potentiometric lead
7.2 Drying Oven, controlled at 110 6 5°C for drying
titration.
sodium sulfate and sodium chloride.
7.3 Desiccator, containing freshly activated silica gel (or
5. Significance and Use
equivalent desiccant) with moisture content indicator.
5.1 Sulfates and chlorides may be found in filter plugging
7.4 Pipettes or Volumetric Transferring Devices, Class A
deposits and fuel injector deposits. The acceptability for use of
glass pipettes or their equivalent of 2.0 cc capacity or auto-
the fuel components and the finished fuels depends on the
matic pipettes fitted with disposable polypropylene tips.
sulfate and chloride content.
7.4.1 Plastic Syringe, 10 cc disposable, optionally fitted
5.2 Total and potential sulfate and total chloride content, as
with a 0.2 µm syringe filter (must be chloride and sulfate-free).
measured by this test method, can be used as one measure of
7.5 Volumetric Flask,ClassAof1LcapacityandClassAof
the acceptability of gasoline components for automotive spark-
10 mL capacity.
ignition engine fuel use.
7.6 Ion Chromatograph,Analytical system with all required
accessoriesincludingsyringes,columns,suppressor,gases,and
6. Interferences
detector.
6.1 Interferences can be caused by substances with similar
7.6.1 Injection System, capable of delivering 25 µL with a
ion chromatographic retention times, especially if they are in
precision better than 1 %.
high concentration compared to the analyte of interest. Sample
7.6.2 Pumping System, capable of delivering mobile phase
dilution or standard addition can be used to minimize or
flows between 0.5 and 1.5 mL/min with a precision better than
resolve most interference problems.
5%.
6.2 A water dip (system void, negative peak as shown in
7.6.3 GuardColumn,forprotectionoftheanalyticalcolumn
Fig. 1) may cause interference with some integrators. Usually,
from strongly retained constituents. Better separations are
for chloride and sulfate determinations, the water dip should
obtained with greater separating power.
not be a problem since the chloride and sulfate peaks are far
7.6.4 Anion Separator Column, capable of producing satis-
enough away from the water dip.
factory analyte separation (see Fig. 1).
6.3 Given the trace amounts of chloride and sulfate deter-
mined by this method, interferences can be caused by contami- 7.6.5 Anion Suppressor Device, micro membrane suppres-
nation of glassware, eluents, reagents, etc. Great care must be sor or equivalent. A cation exchange column in the hydrogen
takentoensurethatcontaminationiskeptatthelowestpossible formhasbeenusedsuccessfully,butitwillperiodicallyneedto
D7328–07
be regenerated as required. This is indicated by a high mL with reagent water, and label this solution as 0.50 N
background conductivity and low analyte response. sulfuric acid. Dilute 100 mL of this concentrate to 2000 mL
7.6.6 Conductivity Detector, low volume (<2 µL) and flow, with reagent water for the final working suppressor solution.
temperature compensated, capable of at least 0 to 1000 µS/cm Other volumes of stock solution may be prepared using
on a linear scale. appropriate ratios of reagents. Follow the specific guidelines
7.6.7 Integrator or Chromatography Data System Software, for this solution from the vendor of the column being used.
capable of measuring peak areas and retention times, and 8.5 Sodium Sulfate, anhydrous, reagent grade, 99 % mini-
correcting the data according to the baseline of the chromato- mum purity. (Warning—Do not ingest; avoid unnecessary
gram. exposure.)
7.7 Gloves, powder-free examination type. 8.6 Sodium Chloride, ACS reagent grade, 99 % minimum
7.8 Hot Block, aluminum, capable of being heated to 65°C purity.
with suitable holes to hold 15 mLglass vials, with a method of 8.7 Ethanol, denatured with methanol, formula 3A or his-
flowing nitrogen over inserted samples. tological grade ethanol, anhydrous, denatured with ethyl ac-
7.9 Glass Vials, 15 mL with screw top. etate, methylisobutyl ketone and hydrocarbon naphtha.
(Warning—Flammable; toxic; may be harmful or fatal if
8. Reagents
ingested or inhaled; avoid skin contact.)
8.1 Purity of Reagents—Reagent grade or higher purity 8.8 Hydrogen Peroxide Solution, 30 %, commercially avail-
able 30 % hydrogen peroxide solution.
chemicals shall be used for the preparation of all samples,
standards, eluents, and regenerator solutions. Unless otherwise 8.9 Nitrogen Gas, 99.99 mol % pure, free of hydrocarbons.
indicated, it is intended that all reagents conform to the
9. Preparation of Standard Solutions
specifications of the Committee on Analytical Reagents of the
American Chemical Society, where such specifications are
9.1 Stock Solutions:
available. Other grades may be used, provided it is first
9.1.1 Sulfate Stock Solution, approximately 2000 mg/L—To
ascertained that the reagent is of sufficiently high purity to
ensure dryness, place anhydrous sodium sulfate (5 g) in a
permit its use without lessening the accuracy of the determi-
drying oven at 110°C for at least an hour, cool and store in a
nation.
desiccator. Accurately weigh 2.96 g anhydrous sodium sulfate
8.2 Purity of Water—Unless otherwise indicated, reference
to the nearest tenth of a milligram and transfer toa1L
to water shall be understood to mean reagent water as defined
volumetric flask. Add Type II water to dissolve the sodium
by Type II in Specification D 1193. For eluent preparation and
sulfate and make to volume. Calculate the concentration of
handling, comply with all ion chromatograph instrument and
sulfate in the solution according to Eq 1. Other volumes of
column vendor requirements (for example, filtering, degassing,
stock solution may be prepared using the appropriate ratio of
etc.).
reagents.
8.3 Eluent Buffer Solution—The eluent solution used de-
stock sulfate ~mg/L! 5 ~gNa SO ! ~0.6764! ~1000 mg/g!/1L (1)
2 4
pends on the systems or analytical columns that are used
(contact instrument and column vendors). For the chromato-
where:
grams in Fig. 1, the following eluent buffer was used: Sodium
gNa SO = weight in grams of Na SO dissolved in 1 L,
2 4 2 4
bicarbonate (NaHCO ) 1.7 mM and sodium carbonate and
(Na CO ) 1.8 mM. Dissolve 2.8563 6 0.0005 g of NaHCO 0.6764 = weight percent sulfate in Na SO .
2 3 3 2 4
9.1.2 Chloride Stock Solution, approximately 2000 mg/
and 3.8157 6 0.0005 g of Na CO in reagent water in a 1-L
2 3
Type A volumetric flask and dilute to volume. Dilute 100 mL 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
of this concentrate to 2000 mL with reagent water for the final
working eluent solution. Other volumes of stock solution may desiccator. Accurately weigh 3.30 g dried sodium chloride to
thenearesttenthofamilligramandtransfertoa1Lvolumetric
be prepared using appropriate ratios of reagents. Follow the
specific guidelines for this solution from the vendor of the flask. Add Type II water to dissolve the sodium chloride and
make to volume. Calculate the concentration of chloride in the
column being used. Alternatively, this solution can be pur-
chased from a qualified vendor. solution according to Eq 2. Other volumes of stock solution
8.4 Suppressor Solution for Membrane Suppressor, 0.025 N may be prepared using the appropriate ratio of reagents.
sulfuric acid. Carefully add 13.7 mL of reagent grade sulfuric
stock chloride ~mg/L! 5 ~g NaCl! ~0.6068! ~1000 mg/g!/1L (2)
acid (relative density 1.84) to approximately 500 mL reagent
where:
water in a 1-Lvolumetric flask. (Warning—This will generate
g NaCl = weight in grams of NaCl dissolved in 1 L, and
a very hot solution.Allow it to cool before diluting to 1000 mL
0.6068 = weight percent chloride in NaCl.
volume. Never add water to concentrated acid!) Dilute to 1000
9.2 Chloride and Sulfate Standards in Water—TypeIIwater
andsulfateandchloridestocksolutionsareaddedtoa1Lglass
volumetric flask according to Table 1 to achieve the desired
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
standard. These standard solutions should be discarded and
listed by the American Chemical Society, see Annual Standards for Laboratory
remade every month.
Chemicals, BDH Ltd., Dorset, U.K., and the United States Pharmacopeia and
9.2.1 Chloride and sulfate stock solutions from 9.1 are
National Formulatory, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. added quantitatively into the flask, mixed quantitatively with
D7328–07
TABLE 1 Volumetric Preparation of Chloride and Sulfate
Suppressor flow: 2 mL/min
Standards in Type II Water
10.1.1.1 Other analytical conditions may be used per the
Chloride and
manufacturer’s instructions. It is important that the resulting
Chloride Stock Sulfate Stock
Sulfate Standards
Solution Solution
chromatogram contain chloride and sulfate peaks with baseline
mg Chloride and
mL mL
Sulfate (each)/L water separation like that shown in Fig. 1. If present in sufficient
-
quantit
...