INTERNATIONAL

STANDARD
INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWEWlYHAPOCIHAR OPrAHM3ALlMR l-l0 CTAH~APTbl3ALWl.ORGANlSATlON INTERNATIONALE DE NORMALISATION

Determination of water - Karl Fischer method

(General method)
Dosage de l’eau - Me’thode de Karl Fischer (Me’thode g&&ale)

First edition - 1978-12-01 iTeh STANDARD PREVIEW

(standards.iteh.ai)
ISO 760:1978
https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
8ec0b8396e76/iso-760-1978

UDC 661 : (543.71 + 543.81) Ref. No. IS0 760-1978 (E)

Descriptors : chemical compounds, chemical analysis, determination of content, water, volumetric analysis, electrometric analysis, Karl
Fischer reagent.

Price based on 12 pages

FOREWORD

IS0 (the International Organization for Standardization) is a worldwide federation

of national standards institutes (IS0 member bodies). The work of developing
International Standards is carried out through IS0 technical committees. Every
member body interested in a subject for which a technical committee has been set
up has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work.

Draft International Standards adopted by the technical committees are circulated

to the member bodies for approval before their acceptance as International
Standards by the IS0 Council.

Prior to 1972, the results of the work of the technical committees were published
as IS0 Recommendations; those documents have subsequently been transformed
into International Standards. As part of iTeh STANDARD PREVIEW
that process, Technical Committee
ISO/TC 47, reviewed IS0 Recommendation R 7609168 and found it technically
suitable for transformation. International (standards.iteh.ai)
Standard IS0 760-I 978 therefore
replaced IS0 Recommendation R 760-I 968.
ISO 760:1978
IS0 Recommendation https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
R 760-1968 had been approved by the member bodies of
the following countries : 8ec0b8396e76/iso-760-1978

Australia Germany, F.R. Poland

Austria Hungary Portugal
Belgium India Romania
Chile Israel Spain
Colombia Italy United Kingdom
Czechoslovakia Japan U.S.S.R.
Egypt, Arab Rep. of Korea, Rep. of Yugoslavia
France Netherlands

The member bod ies of the following countries had expressed disapproval of the
Recommendation on technical grounds

New Zealand
U.S.A.

The member body of the following country disapproved the transformation of

ISO/R 760 into an International Standard :

Netherlands

@ International Organization for Standardization, 1978 l

Printed in Switzerland

ii
 CONTENTS Page

1 Scope and field of application ...............................

2 Principle .............................................

3 Reactions ............................................

4 Reagents and materials. ...................................

5 Apparatus ............................................

6 Visual titration. ........................................

7 Direct electrometric titration. ...............................

................................
iTeh 98STANDARD
Electrometric back-titration
PREVIEW
Test report. ..........................................
(standards.iteh.ai)
Annexes

A StandardizationISO 760:1978
of Karl Fischer reagent with standard
water/methanol solution .................................
https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23- 8
8ec0b8396e76/iso-760-1978
B Typical apparatus for visual or direct electrometric titration. ......... 9

C Typical apparatus for electrometric back-titration. ................ 11

...
III
 iTeh This
STANDARD
page intentionally leftPREVIEW
blank

(standards.iteh.ai)
ISO 760:1978
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8ec0b8396e76/iso-760-1978
INTERNATIONAL STANDARD IS0 760-1978 (E)

Determination of water - Karl Fischer method

(General method)

1 SCOPE AND FIELD OF APPLICATION 4.2 2 -Methoxyethanol (Ethylene glycol monomethyl

ether), not containing more than 0,05 % (m/m) of water. If
This International Standard specifies a general method the reagent contains more than this quantity of water, dry
known as the Karl Fischer methodlll, suitable for the it by distillation, rejecting the first portion of distillate,
determination of free water or water of crystallization in which contains the water.
most solid or liquid chemical products, both organic and
inorganic.
4.3 Pyridine, not containing more than 0,05 % (m/m) of
Precautions are necessary in certain cases and these are water. If the reagent contains more than this quantity of
specified in the appropriate International Standards. water, dry it by distillation, rejecting the first portion of
distillate, which contains the water.
Two methods of titration, depending on whether the end-
point is detected visually or electrometrically, are specified.
The visual method can be used when no electrometric 4.4 Sample solvent : either a mixture containing 4 parts
iTeh STANDARD PREVIEW
apparatus is available but is applicable only to colourless
solutions; it is always a direct titration. The electrometric
by volume of the methanol (4.1) and 1 part by volume of
the pyridine (4.3), or (preferably for determinations with

titration or a back-titration.
(standards.iteh.ai)
method, on the other hand, may involve either a direct
The electrometric method,
compou~~ds containing carbonyl groups) a mixture contain-
ing 4 parts by volume of the 2-methoxyethanol (4.2) and
whether by direct titration or back-titration, is the more 1 part by volume of the pyridine (4.3). In special cases,
accurate, and for this reason is recommended. ISO 760:1978other solvents may be recommended, for example acetic
acid, pyridine or a mixture containing 1 part by volume
https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
of the methanol (4.1) and 3 parts by volume of chloroform.
8ec0b8396e76/iso-760-1978
2 PRINCIPLE

Reaction of any water present in a test portion with a 4.5 Karl Fischer reagent
solution of iodine and sulphur dioxide in a pyridinel
methanol mixture (Karl Fischer reagent), previously Place 670 ml of the methanol (4.1) or the 2-methoxyethanol
standardized by titration with an exactly known mass of (4.2) in a dry brown glass flask, fitted with a ground glass
water (see 6.1, 7.1 and 8.1). stopper and having a capacity slightly greater than 1 litre.
NOTE -Methanol may be replaced by 2-methoxyethanol (ethylene Add about 85 g of iodine. Stopper the flask and shake it
glycol monomethyl ether). With this solvent, a more constant
titration volume is obtained and the reagent can be used with
occasionally until the iodine is completely dissolved. Then
aldehydes and ketones, without using any special technique.[21 add approximately 270 ml of the pyridine (4.3), stopper
the flask again and mix thoroughly. Using the method
described below, dissolve 65 g of sulphur dioxide in this
3 REACTIONS[3] solution, cooling to ensure that the temperature of the
liquid does not exceed 20 “C.
H,O+I, +SO, +3C,H,N+2C,H5N.HI +C,H,N.SO,
NOTE - As the reaction is exothermic, it is necessary to cool the
C,H,N.SO, +ROH + C,H5NH.0S02 OR
flask from the beginning and to maintain it at about 0 ‘C, for
example by immersing it in an ice bath or in crushed solid carbon
dioxide.
4 REAGENTS AND MATERIALS
Replace the ground glass stopper by an attachment for
During the analysis, use only reagents of recognized ana- introducing sulphur dioxide, consisting of a cork bearing
lytical grade and only distilled water or water of equivalent a thermometer and a glass inlet tube 6 mm x8 mm,
purity. reaching to within 10 mm of the bottom of the flask, and
a small capillary tube for connecting to the atmosphere.
4.1 Methanol, not containing more than 0,05 % (m/m)
of water. If the reagent contains more than this quantity Place the whole assembly with the ice bath on a balance
of water, dry it by distillation from magnesium turnings and weigh to the nearest 1 g. Connect the inlet tube to a
activated with iodine. Collect the distillate in a receiver cylinder of sulphur dioxide by means of a flexible connec-
protected from atmospheric moisture by means of a guard tion and a drying tube filled with the desiccant (4.9) and
tube filled with the desiccant (4.9). gently open the tap on the cylinder.

1
IS0 760-1978 (E)

Adjust the rate of flow of sulphur dioxide so that all the Alternatively, activated silica gel may be used as a desiccant.
gas is absorbed without the liquid showing any sign of
rising in the inlet tube. 4.10 Silicone-base grease, for lubricating the ground glass
joints.
Maintain the equilibrium of the balance by gradually in-
creasing the tare, and ensure that the temperature of the
liquid does not rise above 20 “C. Close the tap on the 5 APPARATUS
cylinder as soon as the increase in mass reaches 65 g.
All the glassware used shall be previously dried for 30 min
Immediately remove the flexible connection and reweigh in an oven controlled at approximately 130 ‘C, then allowed
the flask and its inlet attachment. The mass of dissolved to cool and stored in a desiccator containing the desiccant
sulphur dioxide should be between 60 and 70 g. A slight (4.9).
excess is not harmful.

Stopper the flask, mix the solution and leave for at least 5.1 For direct titration (by visual method or electrometric
24 h before using it. In fact, as the result of imperfectly method)
understood reactions which occur in the fresh reagent, the
water equivalent of the reagent decreases rapidly to begin 5.1.1 A suitable form of apparatus for this method is
with and then much more slowly. given in annex B, should no commercial apparatus be
available. This standard apparatus comprises the parts
This water equivalent is between 3,5 and 4,5 mg/ml. It shall described below.
be determined daily if methanol has been used, but may be
determined less frequently if 2-methoxyethanol has been 5.1.1.1 Automatic burette, of capacity 25 ml, with a fine
used. point, graduated in 0,05 ml and protected from atmospheric
It is possible to prepare Karl Fischer reagent having a moisture by a guard tube filled with the desiccant (4.9).
lower water content by diluting the solution prepared as
described above with the sample solvent (4.4). 5.1.1.2 Titration vessel, of effective capacity 100 ml,
iTeh STANDARD
Store the reagent in the dark and protected from atmos-
connected PREVIEW
to the tap of the automatic burette (5.1 .I .I ) by
a ground glass joint and having two side tubes, one permit-

reagent bottle (5.1.1.5).

(standards.iteh.ai)
pheric moisture. It should preferably be stored in the ting the introduction of platinum electrodes if the electro-
metric method is used and the other fitted with a “vaccine
cap” to permit the introduction of liquid test
ISO 760:1978 portions by
4.6 Sodium tartrate dihydrate (Na,C,H,0,.2H,O), or means of a syringe without opening the vessel.
water. https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
8ec0b8396e76/iso-760-1978
5.1.1.3 Platinum electrodes (see figures 1 and 2, annex B),
4.7 Water/methanol, standard solution corresponding to fused to a glass tube enabling them to be introduced into
ml of water per litre. the bottom of the titration vessel (5.1 .I .2) and joined to
two copper wires which in turn are connected to the device
Using a microburette or a pipette, place 1 ml of water in a
for the electrometric detection of the end-point (5.1.1.7).
perfectly dry 100 ml one-mark volumetric flask containing
(These are omitted in the case of the visual method.)
approximately 50 ml of the methanol (4.1). Dilute to the
mark with the methanol and mix. [For standardization of
the Karl Fischer reagent (4.5) with this solution, see 5.1.1.4 Electromagnetic stirrer, operating at a rotational
annex A, clause A.1 or A.2, depending on whether the frequency of 150 to 300 min-‘, with a mild steel bar
visual method or the direct electrometric method is used.] coated with glass or polytetrafluorethylene (PTFE), and
fixed on a base of adjustable height.
1 ml of this standard solution contains 10 mg of water.
5.1 .I .5 Reagent bottle for the Karl Fischer reagent, of
4.8 Water/methanol, standard solution corresponding to capacity approximately 3 litres, of brown glass, in which the
2g of water per litre. filling tube of the automatic burette (5.1 .l.l) is immersed
through the ground glass stopper.
Using a microburette or a pipette, place 1 ml of water in a
perfectly dry 500 ml one-mark volumetric flask containing
5.1 .I.6 Rubber bulb, connected to a Drechsel bottle filled
approximately 100 ml of the methanol (4.1). Dilute to the
with the desiccant (4.9), for the admission of dry air under
mark with the same methanol and mix. (See the corre-
pressure into the reagent bottle (5.1.1.5) in order to fill the
spondence by volume of this solution with the Karl Fischer
automatic burette (5.1.1.1).
reagent in 8.2.2.)

1 ml of this standard solution contains 2 mg of water. 5.1 .I .7 Device for the electrometric detection of the end-
point, shown diagramatically in figure 3, annex B. (This is
4.9 Aluminium sodium silicate, anhydrous, in the form omitted in the case of the visual method.)
of granules of diameter 1,7 mm, for use as a desiccant. The
granules may be regenerated by washing with water and 5.1.2 Medical syringes, of suitable capacity, the volume of
drying at 350 “C for at least 48 h. which is calibrated.
 IS0 7601978 (E)

5.1.3 Small glass tube, closed at one end and fitted at the 6 VISUAL TITRATION
other with a rubber stopper, used for weighing and
introducing into the titration vessel, for example, the mass 6.1 Principle for the detection of the end-point
of sodium tartrate (4.6) (approximately 0,250 g) used to
standardize the Karl Fischer reagent (4.5), or possibly Development of colour in the test portion by addition
test portions of solid products. of the first drop of excess Karl Fischer reagent, coloured
with iodine which gradually becomes colourless on addition
to the test portion containing the water to be determined.
5.2 For electrometric back-titration method

5.2.1 A suitable form of apparatus for this method is given

in annex C, should no commercial apparatus be available. 6.2 Procedure
This standard apparatus comprises the parts described
below.
6.2.1 Standardization of the Karl Fischer reagent

5.2.1.1 Two automatic burettes, of capacity 25 ml, with 6.2.1.1 Assemble the apparatus as shown in ( annex B,
fine points, connected directly to their filling containers, lubricating the joints with the grease (4.10). Introduce by
one of brown glass for the Karl Fischer reagent (4.5) and means of a syringe (5.1.2) 25 ml of the methanol (4.1)
the other for the standard water/methanol solution (4.8). into the titration vessel (5.1 .I .2) through the “vaccine cap”.
Switch on the electromagnetic stirrer (5.1.1.4). In order
5.2.1.2 Titration vessel, of effective capacity 100 ml, to cause reaction of the traces of water present in the
connected to the automatic burettes (5.2.1 .I) by means methanol, add the Karl Fischer reagent (4.5) from the
of ground glass joints and having two side tubes, one automatic burette (5.1.1 .I) until a brown colour is
permitting the introduction of platinum electrodes and the obtained.
other fitted with a “vaccine cap” to permit the introduction
of liquid test portions by means of a syringe without 6.2.1.2 In the small glass tube (5.1.3), weigh, to the nearest
opening the vessel. 0,000 1 g, approximately 0,250 g of the sodium tartrate
iTeh STANDARD PREVIEW (4.6). Place this in the titration vessel very quickly, removing
the “vaccine cap” for a few seconds, then weigh the small
(standards.iteh.ai)
5.2.1.3 Drying tube, connecting the filling containers of
the burettes (5.2.1 .I) and the stopper of the titration vessel glass tube, so as to determine, by difference, the mass (m, i
(5.2.1.2) by a closed circuit. of the sodium tartrate used.
ISO 760:1978
Standardization may also be effected by introducing a mass
5.2.1.4 Platinum electrodeshttps://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
(see figures 4 and 5, annex C),
(m,) of water of approximately 0,040 g from a dropping
8ec0b8396e76/iso-760-1978
fused to a glass tube enabling them to be introduced into bottle, weighed before and after introduction into the
the bottom of the titration vessel (5.1 .I .2) and joined to titration vesse1.l)
two copper wires which in turn are connected to the device
for the electrometric detection of the end-point (5.2.1.6). Titrate the known quantity of water introduced with the
Karl Fischer reagent (4.5) to be standardized, until the
5.2.1.5 Electromagnetic stirrer, operating at a rotational same brown colour as in 6.2.1.1 is obtained, and note the
frequency of 150 to 300 min-’ , with a mild steel bar volume (V, ) of reagent used.
coated with glass or polytetrafluorethylene (PTFE), and
fixed on a base of adjustable height.
6.2.2 Determination
5.2.1.6 Device for the electrometric detectio n of the end-
Empty the titration vessel (5.1 .I .2) by means of its drain
point, shown diagrammatically in figure 3, ann ex B.
tap. Place in it 25 ml (or the volume specified in the pro-
cedure for the product to be analysed) of the methanol
5.2.2 Medical syr inges, of suitable capacity, the volume of (4.1) or other solvent (4.3 or 4.4), using a syringe (5.1.2)
which is calibrated passing through the “vaccine cap”. Switch on the electro-
magnetic stirrer (5.1.1.4). In order to cause reaction of the
5.2.3 Small glass tube, closed at one end and fitted at the traces of water present in the methanol, add the Karl Fischer
other with a rubber stopper, used for weighing and reagent (4.5) from the automatic burette (5.1 .I .l) until a
introducing into the titration vessel, for example, the mass brown colour is obtained.
of sodium tartrate (4.6) (approximately 0,250 g) used to
standardize the Karl Fischer reagent (4.5), or possibly test Introduce the specified test portion by means of a syringe
portions of solid products. in the case of a liquid, or weighed to the nearest 0,000 1 g

I) For standardization with the standard water/methanol solution (4.7), see annex A, clause A.1.

3
I.S0760-1978 E)

in the small glass tube (5.1.3) in the case of a solid powder. T is the water equivalent, in milligrams per millilitre,
Titrate with the Karl Fischer reagent until the same brown of the Karl Fischer reagent, calculated in accordance with
colour is obtained. 6.3.1.

Note the volume ( V2) of Karl Fischer used for the

determination.
7 DIRECT ELECTROMETRIC TITRATION
NOTE - It is advisable to use a test portion such that its water
content corresponds to a volume of Karl Fischer reagent that can be 7.1 Principle for the detection of the end-point
measured with sufficient accuracy. If necessary, increase in
proportion the quantities of solvent and test sample used and then Immersion in the solution of two platinum electrodes
use a titration vessel of suitable capacity.
subjected to a potential difference : while water is present
in the solution, the polarization of the cathode opposes
the passage of a current. Indication of the end-point of the
titration by the depolarization of the cathode accompanied
6.3 Expression of results by a sudden increase in current (which is shown by a
suitable electrical device).
6.3.1 Water equivalent of the Karl Fischer reagent
The water equivalent T of the Karl Fischer reagent (4.5), 7.2 Procedure
expressed in milligrams of water per millilitre of reagent, is
given by the formula 7.2.1 Standardization of the Karl Fischer reagent

m, x0,156 6 m2
7.2.1.1 Assemble the apparatus as shown in figure 1,
T = - or T=r annex B, lubricating the joints with the grease (4.10).
4 1 Introduce by means of a syringe (5.1.2) 25 ml of the
methanol (4.1) into the titration vessel (5.1.1.2) through
where

ml
iTeh STANDARD PREVIEW
is the mass, in milligrams, of the sodium tartrate
the “vaccine cap”. Switch on the electromagnetic stirrer
(5.1 .1.4) and close the circuit of the device for the electro-
metric detection of the end-point (5.1 .I .7).
dardization (6.2.1.2);
(standards.iteh.ai)
(4.6) introduced if this reagent is used for the stan-
Adjust the apparatus so that a potential difference of 1 to
is the mass, in milligrams, of water introduced if ISO 760:1978 2 V is applied to the electrodes and the galvanometer shows
m2
pure water is used for the standardization (6.2.1.2); a low current, usually a few microamperes. In order to
https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
cause reaction of the traces of water present in the methanol,
V, is the volume, in millilitres, of the Karl Fischer8ec0b8396e76/iso-760-1978
add the Karl Fischer reagent (4.5) until the galvanometer
reagent (4.5) used for the standardization; shows a sudden increase in current of about 10 to 20 uA,
which remains stable for at least 1 min.
0,156 6 is the factor for calculation of the water of the
sodium tartrate dihydrate.
7.2.1.2 In the small glass tube (5.1.3), weigh, to the nearest
0,000 1 g, approximately 0,250 g of the sodium tartrate
6.3.2 Water content of the sample
(4.6). Place this in the titration vessel very quickly, removing
The water content of the sample, ressed as a percentage the “vaccine cap” for a few seconds; then weigh the small
by mass, is given by the fo rmula glass tube, so as to determine, by difference, the mass (m3)
of the sodium tartrate used.
V2 x T V2 x T
Standardization may also be effected by introducing a mass
m,xlO Or v() xp x 10 (m,) of water of approximately 0,040 g from a dropping
bottle, weighed before and after introduction into the
titration vessel,l )

mO is the mass, in grams, of the test portion (in the Titrate the known quantity of water introduced with the
case of sol id products); Karl Fischer reagent (4.5) to be standardized, until the
same deflection of the pointer of the galvanometer is
V, is the volume, in millilitres, of the test portion (in
reached and remains stable for at least 1 min. Note the
the case of liquid products);
volume (V,) of reagent used.
p is the density of the sample, in grams per millilitre,
at 20 ‘C (in the case of liquid products); 7.2.2 Determination
V, is the volume, in millilitres, of the Karl Fischer Empty the titration vessel (5.2.1.2) by means of its drain
reagent (4.5) used for the determination (6.2.2); tap. Place in it 25 ml (or the volume specified in the pro-

1) For standardization with the standard water/methanol solution (4.71, see annex A, clause A.2

4
 IS0 7604978 (E)

cedure for the product to be analysed) of the methanol p is the density of the sample, in grams per millilitre,
(4.1) or other solvent (4.3 or 4.4), using a syringe (5.1.2) at 20 “C (in the case of liquid products);
passing through the “vaccine cap”. Switch on the electro-
magnetic stirrer (5.1.1.4). In order to cause reaction of the V4 is the volume, in millilitres, of the Karl Fischer
traces of water present in the solvent used, add the Karl reagent (4.5) used for the determination (7.2.2);
Fischer reagent (4.5), proceeding as specified in 7.2.1 until T is the water equivalent, in milligrams per millilitre,
there is a sudden and constant deflection lasting for at least of the Karl Fischer reagent, calculated in accordance
1 min. *with 7.3.1.
Introduce the specified test portion by means of a syringe
in the case of a liquid or weighed to the nearest 0,000 1 g
8 ELECTROMETRIC BACK-TITRATION
in a small glass tube (5.1.3) in the case of a solid powder.
Titrate with the Karl Fischer reagent using the same electro-
metric procedure for detecting the end-point of the 8.1 Principle for the detection of the end-point
reaction.
Addition of an excess of Karl Fischer reagent which is then
Note the volume (VJ of Karl Fischer reagent used for the back-titrated with a standard water/methanol solution,
determination. Subjection of the electrodes to a very slight potentia!
difference but sufficient to cause a large deflection of the
NOTE - It is advisable to use a test portion such that its water galvanometer pointer at the start of the back-titration-
content corresponds to a volume of Karl Fischer reagent that can be Indication of the end-point of the titration by the polari-
measured with sufficient accuracy. If necessary, increase in
proportion the quantities of solvent and test sample used and then zation of the cathode accompanied by the sudden inter-
use a titration vessel of suitable capacity. ruption of the current (which is shown by a suitable elec-
trical device).
7.3 Expression of results

7.3.1 Water equivalentiTeh STANDARD8.2PREVIEW

of the Karl Fischer reagent Procedure

(standards.iteh.ai)
The water equivalent T of the Karl Fischer reagent (4.5),
expressed in milligrams of water per millilitre of reagent,
8.2.1 Standardization of the Karl Fischer reagent

is given by the formula 8.2.1.1 Assemble the apparatus as shown in annex C,

ISO 760:1978lubricating the joints with the grease (4.10). Place in the
m3 x0,1566 titration vessel (5.2.1.2) sufficient
https://standards.iteh.ai/catalog/standards/sist/1a8f732f-45e2-4f95-9d23-
m4 Karl Fischer reagent
T= v or T =- (4.5) from one of the automatic burettes (5.2.1 .I) to cover
3 V3
8ec0b8396e76/iso-760-1978
the electrodes (5.2.1.4). Switch on the electromagnetic
where stirrer (5.2.1.5) and close the circuit of the device for the
electrometric detection of the end-point (5.2.1.6). Allow
m3 is the mass, in milligrams, of the sodium tartrate the standard water/methanol solution (4.8) to flow from
(4.6) introduced if this reagent is used for the the second automatic burette (5.2.1.1) until the pointer
standardization (7.2.1); of the galvanometer moves suddenly to zero.

m4 is the mass, in mill igrams, of water introduced if

pure water i s used for the standardiz ation; 8.2.1.2 In the small glass tube (5.2.3), weigh, to the
V, is the volume, in millilitres, of the Karl Fischer nearest 0,000 1 g, approximately 0,250 g of the sodium
reagent (4.5) used for the standardization; tartrate (4.6). Place this in the titration vessel very quickly,
removing the “vaccine cap” for a few seconds, then weigh
0,156 6 is the factor for calculation of the water of the small glass tube, so as to determine, by difference,
the sodium tartrate dihydrate. the mass (m,) of the sodium tartrate used.
Standardization may also be effected by introducing
7.3.2 Water con tent of the sample
a mass (mg) of water of approximately 0,040 g from a
The water conte lnt of the sample I expressed as a percentage dropping bottle, weighed before and after introduction
by mass, is given by th e formula into the titration vessel.

V4 x T V4 x T Then add a known excess volume (V,) of the Karl Fischw

reagent, stopping when the solution becomes brown in
m,xlO Or v,xpx10 colour. Wait for 30 s and back-titrate this excess, using
the standard water/methanol solution (4.8), until the
where pointer of the galvanometer moves suddenly to zero. Note
m. is the mass, in gra ms, of the test portion (in the the volume ( Vs) of this solution (4.8) used.
case of sol id products);

VO is the volume , in millil itres, of the test portion (in 8.2.2 Correspondence between the Karl Fischer reagent
the case of liquid p roducts); and the standard water/methanol solu tion