ASTM D3401-97

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 3401 – 97 An American National Standard
Standard Test Methods for
Water in Halogenated Organic Solvents and Their
Admixtures
This standard is issued under the fixed designation D 3401; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3. Summary of Test Methods
1.1 These test methods describe the use of the Karl Fischer 3.1 In the Karl Fischer reaction, water will react with iodine
(KF) titration for determination of water in halogenated or- in the presence of sulfur dioxide, alcohol, and an organic base
ganic solvents and mixtures thereof. Water concentrations from according to the following equation:
2 to 1000 ppm can be determined in these solvents. Two test
H O 1 I 1 SO 1 CH OH 1 3RN → ~RNH!SO CH 1 2~RNH!I
2 2 2 3 4 3
methods are covered as follows:
(1)
1.1.1 Test Method A, Water Determination Using a Coulo-
metric KF Titrator—The coulometric test method is known for
where RN = organic base.
its high degree of sensitivity (typically < 10 μg H O) and
3.2 When the volumetric titration test method is used for
should be the test method of choice if water concentrations are
this determination, the halogenated sample is added to a KF
typically below 50 ppm or if only small amounts of sample are
solvent that usually consists of sulfur dioxide and an amine
available for water determinations. This test method requires
dissolved in anhydrous methanol. This solution is titrated with
the use of equipment specifically designed for coulometric
an anhydrous solvent containing iodine. The iodine titrant is
titrations.
first standardized by titrating a known amount of water.
1.1.2 Test Method B, Water Determination Using a Volumet-
3.3 In the coulometric titration test method, the sample is
ric KF Titrator—The volumetric test method is a more
injected into an electrolytic cell where the iodine required for
traditional approach to KF water determinations. Although
the reaction with water is produced by anodic oxidation of
titrators are specifically designed for KF volumetric determi-
iodide. With this technique, no standardization of reagents is
nations, many automatic titrators on the market can be adapted
required.
to perform KF titrations.
3.4 In both test methods, the end point is determined
1.2 Either of these test methods can be used to determine
amperometrically with a platinum electrode that senses a sharp
typical water concentrations (15 to 500 ppm) found in haloge-
change in cell resistance when the iodine has reacted with all
nated solvents.
of the water in the sample.
1.3 These test methods recommend the use of commercially
available Karl Fischer titrators and reagents. 4. Significance and Use
1.4 This standard does not purport to address all of the
4.1 High water concentrations can have a detrimental effect
safety concerns, if any, associated with its use. It is the
on many uses of halogenated solvents.
responsibility of the user of this standard to establish appro-
4.1.1 Water can cause corrosion and spotting when solvents
priate safety and health practices and determine the applica-
are used for metal cleaning.
bility of regulatory limitations prior to use. For specific
4.1.2 Water can reduce the shelf life of aerosol formula-
precautionary statements, see Sections 11 and 15.
tions.
4.1.3 Water can inhibit desired reactions when solvents are
2. Referenced Documents
used in formulations.
2.1 ASTM Standards:
E 203 Test Method for Water Using Karl Fischer Titration 5. Interferences
5.1 Certain compounds or classes of compounds interfere
with the accurate determination of water by the Karl Fischer
These test methods are under the jurisdiction of ASTM Committee D-26 on
test method. They include aldehydes, ketones, free halogens,
Halogenated Organic Solvents and Fire Extinguishing Agents and are the direct
ferric salts, and strong oxidizing and reducing agents.
responsibility of Subcommittee D26.04 on Test Methods.
Current edition approved Dec. 10, 1997. Published May 1998. Originally
5.2 Free halogens can oxidize the iodate in the KF reagents
published as D 3401 – 75. Last previous edition D 3401 – 96.
to form iodine; this causes erroneously low water values.
Annual Book of ASTM Standards, Vol 15.05.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3401
5.3 A more detailed discussion of KF interferences can be 8.4 Transfer solvent to the bottles as quickly as possible.
,
3 4
found in Test Method E 203 and other sources. Adjust the liquid level to come within 1 in. of the top of the
bottle. Immediately place the cap on the bottle and tighten.
6. Apparatus
8.5 When removing a portion of sample from the bottle for
6.1 Coulometric Titrator, (for Test Method A only) con- KF analysis, use pipets or syringes that have been thoroughly
sisting of a single or dual bath electrolytic cell, dual platinum dried. Replace the cap on the bottle immediately.
electrode, magnetic stirrer, and control unit. 8.6 If more than one portion of sample is to be taken from
6.2 Volumetric Titrator, (for Test Method B only) consist- the bottle or if the sample is to be retained for further water
ing of a titration cell, dual platinum electrode, magnetic stirrer, analysis, it is a good practice to blanket the top of the bottle
dispensing buret, and control unit. with dry nitrogen when removing the sample. If septum cap
6.3 Syringes, 2, 5, 10, or 20-mL sizes. closures are being used, dry nitrogen can be introduced with a
6.4 Syringe, 5-μL size. syringe at the same time a portion of the sample is being
6.5 Silicon Rubber Blocks or Silicon Rubber Septa.
removed with a second syringe.
6.6 Drying Oven, air circulating.
TEST METHOD A—WATER DETERMINATION
6.7 Desiccator.
USING A COULOMETRIC KF TITRATOR
6.8 Analytical Balance, capable of weighing to 60.01 g.
9. Summary of Test Method
7. Reagents
9.1 The dual bath coulometric titration cell consists of a
7.1 Anode Reagent, for dual bath titration (for Test Method
sealed vessel containing both an anode and cathode compart-
A only), use reagent recommended by manufacturer of titrator.
ment. The anodic compartment usually contains a solution
7.2 Cathode Reagent, for dual bath titration (for Test
consisting of sulfur dioxide, iodide, and an amine in a
Method A only), use reagent recommended by manufacturer of
methanol/chloroform solvent. The cathodic compartment con-
titrator.
tains similar reagents optimized for cathodic reduction.
7.3 Single Bath Reagent, (for Test Method A only), use
9.2 When a sample containing water is injected into the
reagent recommended by manufacturer of titrator.
anode compartment, the electrolytic cell generates its own
7.4 Karl Fischer Volumetric Titrant, (for Test Method B
supply of iodine from the iodide present. The iodine reacts
only) typically consists of a mixture of an organic amine, sulfur
stoichiometrically with the water and the completion of the
dioxide, and iodine dissolved in a non-hydroscopic solvent(s).
reaction is detected with a platinum sensing electrode. The
Reagents with titers of 1.00, 2.00, and 5.00 mg of H O/mL can
coulombs of electricity required to generate the necessary
be commercially obtained.
amount of iodine is then translated by the microprocessor in the
7.5 Karl Fischer Solvent, (for Test Method B only)
control unit into the amount of water that was present in the
typically consists of a mixture of an organic amine and sulfur
sample.
dioxide dissolved in anhydrous methanol.
9.3 The single bath coulometric titration cell consists of a
NOTE 1—Pyridine was the organic amine that was traditionally used in
sealed vessel filled with single bath reagent and dual platinum
Karl Fisher reagents, however, pyridine-free formulations are now avail-
electrodes. When a sample containing water is injected into the
able and preferred by most KF instrument manufacturers for use with their
vessel, the electrolytic cell generates its own supply of iodine
equipment. Pyridine-free reagents are said to be less toxic, less odorous,
from the iodide present in the single bath reagent. The iodine
and more stable than pyridine types.
reacts stoichiometrically with the water and the completion of
8. Sampling
the reaction is detected by a platinum sensing electrode. The
8.1 Since halogenated solvents normally contain low con- coulombs of electricity required to generate the necessary
centrations of water, care must be taken to eliminate the amounts of iodine is then translated by the microprocessor in
introduction of water from sampling equipment and atmo- the control unit into the amount of water that was present in the
spheric moisture. sample.
8.2 Without taking the proper sampling precautions, more
10. Verification of Instrument Accuracy
error is typically introduced into the determination of water
through sampling techniques than in the titration process itself.
10.1 Coulometric titrators do not have a titrant that needs to
8.3 Dry sample bottles and closures in an oven at 110°C for be standardized since the iodine is being generated on demand
several hours. Place caps on the bottles immediately after
by the titration cell. However, occasional checks of the
removing from the oven. instrument accuracy are recommended. This can be done by
titrating a known amount of water and comparing this amount
with the amount of water reported by the titrator.
Mitchell, J., Jr. and Smith, D. M., Aquametry—A Treatise on Methods for the
10.2 Use a 5-μL syringe to inject exactly 3.0 μL of water
Determination of Water, Part III—The Karl Fischer Reagent, 2nd ed., J. Wiley and
into the titration cell. Once the titration is complete, the titrator
Sons, Inc., New York, NY, 1977.
should report a value of 3000 μg (3.0 mg) H O. The deviation
Hydranal—Eugen Scholz Reagents for Karl Fischer Titration, 4th ed., by
Riedel-deHaen Aktiengesellschaft (US Distributor—Cresent Chemical Co., Inc.).
from this value should not be larger than 10 %. If the value is
Automatic coulometric and volumetric titrators are manufactured by many
larger than 10 %, consult the instrument manual or manufac-
different companies. Models that have been found satisfactory for this purpose are
turer to determine the cause.
available from Fisher Scientific, EM Science, Metrohm, Mettler, Photovolt, Mit-
subishi, and others. 10.3 Alternatively, standard solutions containing known
D 3401
amounts of water dissolved in either methanol or a non- 12.7 Transfer the filled syringe to an analytical balance and
hydroscopic solvent are available from reagent suppliers for weigh the syringe and contents to the nearest 0.01 g.
accuracy verification. A known volume of this solution is 12.8 Remove the silicone block and insert the needle into
titrated and the reported amount of water is compared with the the titration cell septum. Inject the sample slowly, taking care
theoretical amount stated by the supplier. not to touch the needle to the surface of the anode solution.
While the syringe is still inside the cell, draw any remaining
11. Precautions
sample that may remain in the syringe needle back into the
11.1 Amounts of coulomatic reagents usually recommended
barrel and remove the needle from the cell.
for addition to the reaction cell typically have the capacity to
12.9 Place the silicone block back onto the tip of the needle
react with approximately 100 to 200 mg of water. These
and reweigh the empty syringe. The weight difference between
reagents must be replaced when they are depleted.
the first and second weighings will be the amount of sample
11.2 Coulomatic reagents are hydroscopic and must be
injected into the titration cell.
stored in tightly capped containers to reduce the absorption of
12.10 The make and model of the titrator being used will
atmospheric moisture.
determine the actual steps performed to carry out the titration
11.3 Since the titrator automatically generates iodine to
process. In most cases, all that is required is pressing a start
keep the reaction vessel in a dehydrated state, it is important to
titration or run key on the instrument keyboard either just prior
keep the cell sealed to prevent introduction of excess atmo-
to or just after the sample injection.
spheric moisture that will decrease reagent life.
12.11 Once the titration is complete, the amount of water
11.4 The total amount of solution in the anode compartment
(μg or mg) that was found in the solvent will appear on the
can affect the KF reaction. Typically, the total volume of
instrument’s digital display. Most instruments will also calcu-
sample liquids that are added to the reaction cell should not
late concentrations (ppm or %) if the sample weight is keyed
exceed 50 % of the original reagent in the compartment. If the
into the instrument’s control panel.
reagents become too dilute, the stoichiometry and rate of the
13. Calculation
Karl Fischer reaction can be adversely affected. This fact
should be considered when using large sample sizes. 13.1 Calculate the water content of the solvent as follows:
11.5 Follow the recommended maintenance procedures of
ppm H O 5 μg H O found/grams of solvent injected (2)
2 2
the instrument manufacturer.
12. Procedure TEST METHOD B—WATER DETERMINATION
USING A VOLUMETRIC KF TITRATOR
12.1 Set up the coulometric titrator according to the manu-
facturer’s instructions, and add the proper amount of coulomat
14. Summary of Test Method
reagents to the anode and cathode compartments of the titration
14.1 The volumetric titration cell consists of a sealed glass
cell.
vessel containing a dual platinum electrode. To the cell, a
12.2 The cell solutions must be anhydrous prior to introduc-
suitable solvent (usually methanol based) is added. The sample
tion of the sample. This is accomplished by either pretitrating
is injected into the cell, the mixture is stirred thoroughly and
the cell contents or by adding a small amount of an iodine/
titrated with a Karl Fischer reagent. This reagent typically
methanol solution until a faint brownish coloration appears.
contains an organic amine, sulfur dioxide, and iodine dissolved
Following the procedure recommended by the instrument
in a non-hydroscopic solvent such as xylene. The iodine reacts
manufacturer is suggested.
stoichiometrically with the water, and the completion of the
12.3 The amount of halogenated solvent that is injected into
reaction is detected with the platinum electrode.
the cell depend
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