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For highest standards.Water determination according to Karl Fischer

Water is a vital substance that we meet in its various forms regularly. However, it is

sometimes undesirable and sometimes its presence may cause considerable technical

problems resulting in high costs. Water may affect the chemical and physical properties

of substances and influence the quality, price and the shelf-life of a product.

Using the Karl Fischer titration together with our Apura reagents from Merck Millipore,

the water content of gases, liquids and solids can be determined easily and with a

high degree of accuracy. Not without reason is no other method as widespread as this

one: Determination of water content according to Karl Fischer is rapid, accurate and

reliable; it is thus the method of choice in quality and in-process control, production and

research & development. Our laboratories are not only working in the development

of applications, but are continuously striving to ascertain appropriate reagents and stan-

dards. The latest results are always shown in our Apura product line for Karl Fischer

titration. Apura means aqua pure analysis.

Brilliant results with Apura

Since we apply the highest standards to produc-

tion processes and stringent testing requirements,

Apura reagents and standards are distinguished

by excellent quality. The measuring results are

therefore always reliable and accurate. From the

selection of raw materials, packaging on up to

quality control of the finished reagents we apply

the strictest standards. This ensures a sophisticated

consistency, quality and thus comparable and

transparent results. The certificates of analysis for

reagents and standards contain all the information

important for quality management documentation.

Precise water determination every time The standard for reproducible results

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The significance of Karl Fischer titration is empha-

sized by the fact that it has been included in the

most important Pharmacopoeias, ASTM (American

Standard Methods), German industrial norm DIN

EN ISO 9001/2008 and other guidelines. Together

with our Apura standards the Karl Fischer product

line from Merck Millipore is always reliable, rapid,

accurate and globally available to facilitate inter-

national product transfer.

5 with 30 years of experienceA proven method, modified according to the latest research

We use only high-quality and approved raw materials. This ensures batch-to-batch consistency and

comparable analytical results.

You benefit from our high scientific standards and our long international experience.

Merck Millipore in particular places great importance on safety. For this reason, the Apura Karl

Fischer reagents contain no toxic components or, if this is not possible, they are limited to a minimum.

Our international sales network and local offices ensure safe delivery and service worldwide.

Whenever you need help, we can supply it via our application and development laboratories.

Here we can advise you on applications, offer technical support, and assist you in validation projects.

Contact us at [email protected] or visit our application finder:

www.merckmillipore.com/applicationfinder-apura

Our quality control is carried out according to the most stringent standards. Analyses are carried out

using recognized international standards. This renders the results achieved completely transparent.

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The Karl Fischer titration A long tradition

Since their development in the 1930s, Karl Fischer titrations have found use worldwide. With this method

the water contents of a large variety of materials can be determined over a wide concentration range

from 1 ppm to 100 %. In contrast to other methods, the Karl Fischer titration is based on a chemical reac-

tion with water, so that water is exclusively determined. The Karl Fischer titration has a wide spectrum of

applications and is used in a broad range of fields, for example water determination in foodstuffs, chemi-

cals, pharmaceuticals, cosmetics and mineral oils.

The reaction mechanism

The basis for the determination of water content according to Karl Fischer is the oxidation of sulfur dioxide

by iodine in the presence of water as described by Bunsen:

2 H2O + I2 + SO2 H2SO4 + 2 HI

This chemical reaction was utilized by Karl Fischer in determining water volumetrically; he used a solution

of iodine and sulfur dioxide in a non-aqueous solvent. The acid released by the reaction was at that time

neutralized by the base pyridine. Today the toxic pyridine has been replaced by other non-toxic bases.

Although the Karl Fischer titration is a long-established method, the actual reaction mechanism has never

been completely clarified. However, due to precise knowledge of the reaction process, systematic improve-

ment of the method and the use of new solvents, research into the reaction method was continued. The

main reaction thus proceeds according to the following 2-step mechanism:

CH3OH + SO2 + RN [RNH]SO3CH3

[RNH]SO3CH3 + I2, I3- + H2O + 2 RN [RNH]SO4CH3 + 2 [RNH]I

(R = Alkyl component)

Initially, Smith, Bryant and Mitchell established the participation of methanol in the reaction and hence

were able to correct the faulty stoichiometry of the reaction as established by Karl Fischer. The most

important kinetic papers published during the 70s indicated that the base itself did not participate in the

reaction; it acted more in the role of a buffer. The optimal working range of titration in which rapid and

stoichiometric reaction is ensured is between pH 5 and pH 7. Latest results now indicate that, under Karl

Fischer conditions, mainly alkyl sulfite is oxidized.

1.

2.

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Two methods: Volumetry and Coulometry

Two methods are available for the determination of water using

the Karl Fischer method: a volumetric and a coulometric method.

The method selected depends primarily on the amount of water

to be determined.

Volumetry

In the case of higher levels of water (0.1100 %), the volumetric

method should be used. For volumetric titration, we supply both one

component and two component reagents.

Coulometry

For very low levels of water (< 1 %) or for water determination of

very expensive substances with small sample amount, the coulo-

metric method should be used. In this case, a difference is made

between cells with and without a diaphragm. For both cell types,

the appropriate Apura reagents are available.

Standards

The Apura range is rounded off with water standards for monitor-

ing and qualification of Karl Fischer instruments, for checking mea-

suring results and titer determination.

Karl Fischer 19011958

The discoverer Karl Fischer, a mineral oil chemist whose

name was given to the method he established for deter-

mining the water content of substances, actually discov-

ered the method by chance. During a search for a method

for determining the water content of liquid sulfur dioxide,

he remembered the well-established Bunsen equation.

Fischer, fascinated by chemistry since his childhood, was

at the time employed by a German mineral oil company

to monitor the construction and commissioning of

new refi neries throughout the world. In 1935, he pub-

lished the results of his research in the Journal for

Applied Chemistry under the title A new procedure for

the volumetric analysis of the water content of liquids

and solids. Due to its universal applicability, the Karl

Fischer titration has been established today as the method

for water determination.

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The right method for any applicationBenefit from our experience

TitrantsCombiTitrant 5

[188005]

Titrant 5

[188010]

CombiTitrant 5 Keto

[188006]

CombiTitrant 2

[188002]

Titrant 2

[188011]

CombiTitrant 1

[188001]

CombiCoulomat frit

[109255]

CombiCoulomat fritless

[109257]

Standards

VolumetrySee page 10

CoulometrySee page 18

Standards See page 22

0.1

100 %

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ater

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apura

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