ASTM D4928-00(2010)
(Test Method)Standard Test Methods for Water in Crude Oils by Coulometric Karl Fischer Titration
Standard Test Methods for Water in Crude Oils by Coulometric Karl Fischer Titration
SIGNIFICANCE AND USE
A knowledge of the water content of crude oil is important in the refining, purchase, sale, or transfer of crude oils.
SCOPE
1.1 This test method covers the determination of water in the range from 0.02 to 5 mass or volume % in crude oils. Mercaptan (RSH) and sulfide (S− or H2S) as sulfur are known to interfere with this test method, but at levels of less than 500 μg/g (ppm), the interference from these compounds is insignificant (see Section 5).
1.2 This test method can be used to determine water in the 0.005 to 0.02 mass % range, but the effects of the mercaptan and sulfide interference at these levels has not been determined.
1.3 This test method is intended for use with standard commercially available coulometric Karl Fischer reagent.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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. For specific hazard statements, see Section 7.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D4928–00 (Reapproved 2010)
Designation: Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9
Designation: 386/99
Standard Test Method for
Water in Crude Oils by Coulometric Karl Fischer Titration
This standard is issued under the fixed designation D4928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D4177 Practice for Automatic Sampling of Petroleum and
Petroleum Products
1.1 This test method covers the determination of water in
D5854 PracticeforMixingandHandlingofLiquidSamples
the range from 0.02 to 5 mass or volume % in crude oils.
−
of Petroleum and Petroleum Products
Mercaptan (RSH) and sulfide (S or H S) as sulfur are known
E203 TestMethodforWaterUsingVolumetricKarlFischer
to interfere with this test method, but at levels of less than
Titration
500µg/g (ppm), the interference from these compounds is
2.2 API Standards:
insignificant (see Section 5).
MPMS Chapter 8.1 Practice for Manual Sampling of Petro-
1.2 This test method can be used to determine water in the
leum and Petroleum Products (ASTM Practice D4057)
0.005 to 0.02 mass % range, but the effects of the mercaptan
MPMS Chapter 8.2 Practice for Automatic Sampling of
and sulfide interference at these levels has not been deter-
Petroleum and Petroleum Products (ASTM Practice
mined.
D4177)
1.3 This test method is intended for use with standard
MPMS Chapter 8.3 Practice for Mixing and Handling of
commercially available coulometric Karl Fischer reagent.
Liquid Samples of Petroleum and Petroleum Products
1.4 The values stated in SI units are to be regarded as
(ASTM Practice D5854)
standard. No other units of measurement are included in this
standard.
3. Summary of Test Method
1.5 This standard does not purport to address all of the
3.1 After homogenizing the crude oil with a mixer, an
safety concerns, if any, associated with its use. It is the
aliquot is injected into the titration vessel of a Karl Fischer
responsibility of the user of this standard to establish appro-
apparatus in which iodine for the Karl Fischer reaction is
priate safety and health practices and determine the applica-
generatedcoulometricallyattheanode.Whenallthewaterhas
bility of regulatory limitations prior to use. For specific hazard
been titrated, excess iodine is detected by an electrometric
statements, see Section 7.
end-point detector and the titration is terminated. Based on the
2. Referenced Documents stoichiometry of the reaction, one mole of iodine reacts with
one mole of water, thus the quantity of water is proportional to
2.1 ASTM Standards:
the total integrated current according to Faraday’s Law.
D1193 Specification for Reagent Water
3.2 The precision of this test method is critically dependent
D4057 Practice for Manual Sampling of Petroleum and
ontheeffectivenessofthehomogenizationstep.Theefficiency
Petroleum Products
of the mixer used to achieve a homogeneous sample is
determined by the procedure given in Practice D5854 (API
This test method is under the jurisdiction of ASTM Committee D02 on
MPMS Chapter 8.3).
Petroleum Products and Lubricants and theAPI Committee on Petroleum Measure-
3.3 Two procedures are provided for the determination of
ment, and is the direct responsibility of Subcommittee D02.02.10 on Sediment and
water in crude oils. In one procedure, a weighed aliquot of
Water (API MPMS Chapter 10.0).
sample is injected into the titration vessel and the mass % of
CurrenteditionapprovedJune1,2010.PublishedJuly2010.Originallyapproved
in 1989. Last previous edition approved in 2005 as D4928–00 (2005). DOI:
10.1520/D4928-00R10.
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 Published as Manual of Petroleum Standards. Available from American
Standards volume information, refer to the standard’s Document Summary page on Petroleum Institute (API), 1220 L. St., NW, Washington, DC 20005-4070, http://
the ASTM website. www.api.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4928–00 (2010)
water is determined. The other procedure provides for the 6.3.1.2 Syringes, 250 µL, 500 µL, and 1000 µL (1 mL), for
direct determination of the volume % of water in the crude oil crudeoilsamples.Forthevolumetricdeterminationprocedure,
bymeasuringthevolumeofcrudeoilinjectedintothetitration the syringes should be accurate to 5 µL, 10 µL, and 20 µL
vessel. (0.02mL), respectively.
7. Reagents and Materials
4. Significance and Use
7.1 Purity of Reagents—Reagent grade chemicals shall be
4.1 A knowledge of the water content of crude oil is
used in all tests. Unless otherwise indicated, it is intended that
important in the refining, purchase, sale, or transfer of crude
all reagents shall conform to the specifications of the Commit-
oils.
tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available. Other grades may be
5. Interferences
used, provided it is first ascertained that the reagent is of
5.1 A number of substances and classes of compounds
sufficiently high purity to permit its use without lessening the
associated with condensation or oxidation-reduction reactions
accuracy of the determination.
interfereinthedeterminationofwaterbyKarlFischer.Incrude
7.2 Purity of Water—Unlessotherwiseindicated,references
oils, the most common interferences are mercaptans and
to water shall be understood to mean reagent water as defined
sulfides(nottotalsulfur).Atlevelsoflessthan500µg/g(ppm)
by Type IV of Specification D1193.
(as sulfur), the interference from these compounds is insignifi-
7.3 Xylene, reagent grade. Less than 0.05 % water.
cant. Most crude oils, including crude oils classified as “sour
(Warning—Flammable. Vapor harmful.)
crude,”havemercaptanandsulfidelevelsoflessthan500µg/g
7.4 Karl Fischer Reagent—Standard commercially avail-
(ppm) as sulfur. For more information on substances that
able reagents for coulometric Karl Fischer titrations.
interfereinthedeterminationofwaterbyKarlFischertitration
7.4.1 Anode Solution, shall be 6 parts of commercial Karl
method (see Test Method E203).
Fischer anode solution with 4 parts of reagent grade xylene.
5.2 The significance of the mercaptan and sulfide interfer-
Fresh Karl Fischer anode solution shall be used. Anode
ence on the Karl Fischer titration for water levels in the 0.005
solution shall not be used past its expiration date. Anode
to 0.02 mass % range has not been determined experimentally.
solution should be replaced after 7 days in the titration vessel.
At these low water levels, however, the interference may be
(Warning—Flammable, toxic by inhalation and if swallowed,
significant for mercaptan and sulfide levels of less than
avoid contact with skin.)
500µg/g (ppm) (as sulfur).
NOTE 1—Other proportions of anode solution and xylene can be used
and should be determined for a particular reagent and apparatus. The
6. Apparatus
precision and bias were established using the designated anode solution
6.1 Karl Fischer Apparatus, using electrometric end-point.
and xylene.
Presently there are available on the market a number of
7.4.2 Cathode Solution, use standard commercially avail-
commercial coulometric Karl Fischer titration assemblies.
able Karl Fischer cathode solution. Cathode solution shall not
Instructions for operation of these devices are provided by the
beusedaftertheexpirationdateandshouldbereplacedafter7
manufacturer and not described herein.
days in the titration vessel. (Warning—Flammable, can be
6.2 Mixer, to homogenize the crude sample.
fatal if inhaled, swallowed, or absorbed through skin. Possible
6.2.1 Non-Aerating, High-Speed, Shear Mixer—The mixer
cancer hazard.)
shall be capable of meeting the homogenization efficiency test
described in Practice D5854 (API MPMS Chapter 8.3). The
8. Sampling and Test Specimens
samplesizeislimitedtothatsuggestedbythemanufacturerfor
8.1 Samplingisdefinedasallthestepsrequiredtoobtainan
the size of the mixing probe.
aliquotrepresentativeofthecontentsofanypipe,tank,orother
6.2.2 Circulating sample mixers, such as those used with
system and to place the sample into a container for analysis by
automatic crude oil sampling receivers, are acceptable provid-
a laboratory or test facility. The laboratory sample container
ing they comply with the principles of Practice D5854 (API
and sample volume shall be of sufficient dimensions and
MPMS Chapter 8.3).
volume to allow mixing as described in 8.4.
6.3 Syringes:
8.2 Laboratory Sample—The sample of crude oil presented
6.3.1 Samples are most easily added to the titration vessel
tothelaboratoryortestfacilityforanalysisbythistestmethod.
by means of accurate glass syringes with LUER fittings and
Only representative samples obtained as specified in Practice
hypodermic needles of suitable length. The bores of the
D4057 (API MPMS Chapter 8.1) and Practice D4177 (API
needles used should be kept as small as possible but large
MPMS Chapter 8.2) shall be used to obtain the laboratory
enough to avoid problems arising from back pressure and
sample.
blocking while sampling. Suggested syringe sizes are as
follows:
6.3.1.1 Syringe, 10 µL with a needle long enough to dip
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
below the surface of the anode solution in the cell when
listed by the American Chemical Society, see Analar Standards for Laboratory
inserted through the inlet port septum. This syringe is used in
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
the calibration step (Section 10). It should be of suitable
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
graduations for readings to the nearest 0.1 µL or better. MD.
D4928–00 (2010)
TABLE 1 Approximate Test Specimen Size Based on Expected
9.4 Add to the cathode (inner) compartment the Karl Fis-
Water Content
cher cathode solution to a level 2 to 3 mm below the level of
Expected Water Sample Size,
the solution in the anode compartment.
Water Titrated, µg
Content, % gormL
9.5 Turn on the apparatus and start the magnetic stirrer for
0.02–0.1 1.0 200–1000
a smooth stirring action. Allow the residual moisture in the
0.1–0.5 0.5 500–2500
titration vessel to be titrated until the end-point is reached.
0.5–5.0 0.25 1250–12500
NOTE 3—Highbackgroundcurrentforaprolongedperiodcanbedueto
moisture on the inside walls of the titration vessel. Gentle shaking of the
vessel (or more vigorous stirring action) will wash the inside with
NOTE 2—Examples of laboratory samples include sample bottles from
electrolyte.Keepthetitratorontoallowstabilizationtoalowbackground
manual sampling, receptacles from automatic crude oil samplers, and
current.
storage containers holding a crude oil from a previous analysis.
8.3 Test Specimen—The sample aliquot obtained from the
10. Standardization
laboratory sample for analysis by this test method. Once
10.1 In principle, standardization is not necessary since the
drawn, the entire portion of the test specimen will be used in
water titrated is a direct function of the coulombs of electricity
the analysis. Mix the laboratory sample properly as described
consumed. However, reagent performance deteriorates with
in 8.4 before drawing the test specimen.
use and shall be regularly monitored by accurately injecting
8.4 Mix the laboratory sample of crude oil immediately
10µLofpurewater.Suggestedintervalsareinitiallywithfresh
(within 15 min) before drawing the test specimen to ensure
reagent and then after every ten determinations (see Section
complete homogeneity. Mix the sample at room temperature
11.1.3). If the result is outside 10000 6 200 µg, replace both
(15 to 25°C) or less in the laboratory sample container and
the anode and cathode solutions.
record the temperature of the sample in degrees Celsius
immediately before mixing. The type of mixer depends on the
11. Procedure
quantityofcrudeoilinthelaboratorysamplecontainer.Before
11.1 Mass Determination of Sample Size:
any unknown mixer is used, the specifications for the homog-
11.1.1 Add fresh solvents to the anode and cathode com-
enization test, Practice D5854 (API MPMS Chapter 8.3), shall
partments of the titration vessel and bring the solvent to
be met. Reevaluate the mixer for any changes in the type of
end-point conditions as described in Section 9.
crude, volume of crude in the container, the shape of the
11.1.2 Add an aliquot of the crude oil test specimen to the
container, or the mixing conditions (such as mixing speed and
titration vessel immediately after the mixing step described in
time of mixing).
8.4 using the following method.
8.5 Forsmalllaboratorysamplecontainersandvolumes,50
11.1.2.1 Starting with a clean, dry syringe of suitable
to500mL,anon-aerating,high-speed,shearmixerisrequired.
capacity (see Table 1 and Note 4), withdraw at least three
Use the mixing time, mixing speed, and height of the mixer
portions of the sample and discard to waste. Immediately
probe above the bottom of the container found to be satisfac-
withdraw a further portion of sample, clean the needle with a
tory in Practice D5854 (API MPMS Chapter 8.3). For larger
paper tissue, and weigh the syringe and contents to the nearest
containersandvolumes,appropriatemixingconditionsshallbe
0.1mg.Inserttheneedlethroughtheinletportseptum,startthe
defined by following a set of procedures similar to those
titration and with the tip of the needle just below the liquid
outlined in Practice D5854 (API MPMS Chapter 8.3) and
surface, inject the sample. Withdraw the syringe and reweigh
Practice D4177 (API MPMS Chapter 8.2) but modified for
the syringe to the nearest 0.1 mg. After the end-point is
applicationtothelargercontainersandvolumes.Cleananddry
reached, record the titrated water from the digital readout on
the mixer between samples.
the instrument.
8.6 RecordthetemperatureofthesampleindegreesCelsius
immediately after homogenization. The rise in temperature NOTE 4—If the concentration of water in the sample is completely
unknown, it is advisable to start with a small trial portion of sample to
betweenthisreadingandtheinitialreadingbeforemixing(8.4)
avoid excessive titration time and depletion of the reagents. Further
is not to exceed 10°C, otherwise loss of water can occur or the
adjustment
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