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05 / 2004
KF_01_04_e
Determination of the bromine number, or alternatively,
the bromine index
Principle of measurement
The determination of the bromine number, or alternatively, the bromine index, in organic
compounds or mixtures (e.g., oils) is done using the Karl Fischer titrator AQUA 40.00. Both
values specify the percentage of substances that react with bromine under chosen
conditions.
bromine index: specifies the amount of bromine [mg] consumed by 100 g of sample [mg
Br/100 g]
bromine number: specifies the amount of bromine [g] consumed by 100 g of sample [g
Br/100 g]
Here, mainly the portion of unsaturated hydrocarbon is determined. The products are
dissolved in dichloromethane or chloroform. Then the solutions are injected directly into the
measuring cell of the AQUA 40.00. The unsaturated hydrocarbon is titrated microcoulometrically with bromine.
The electrolyte is composed of as follows:
70 ml – KBr solution – (24 g KBr p.a. solved in 100 ml destillated water)
300 ml – glacial acetic acid p.a.
130 ml – methanol p.a.
500 ml electrolyte
Cyclohexene (theoretical bromine number: 194.5 g Br/100 g), 1-octen (theoretical bromine
number: 142.4 g Br/100 g) or styrene (theoretical bromine number: 153.4 g Br/100 g) can be
used as testing substances. These substances are then dissolved with trichlormethane
(chloroform) or dichlormethane (0.5 g of sample in 50 ml dissolvent). 0.3–1 ml of this solution
is used for analysis and dosed directly into the measuring cell.
Titration
The micro-coulometric titration takes place automatically and in a very short period of time
(duration of analysis : approximately 2–7 minutes).
The software includes an integrated formula generator that easily and comfortably enables
both the correction of blank readings of the dissolvent and the conversion of measured
values into the preferred unit of measurement parallel to determination (Fig. 1).
1/5
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, Internet: http://www.ech.de, E-Mail: [email protected]
05 / 2004
KF_01_04_e
Measurement parameters – form for the used formulas
The preset formula contains special parameters for this method:
weighted sample:
the weighed amount of matter of a sample to be disolved in a solvent
and who’s bromine number is to determined (i.e. cyclohexene, [mg])
Fig. 1: The AQUA 40.00’s formula
generator
2/5
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, Internet: http://www.ech.de, E-Mail: [email protected]
05 / 2004
KF_01_04_e
Volume:
the amount of disolved sample (µl) dosed into the measuring cell using a
syringe
Volume LM: the amount of an adaquate solvent used for disolving the weighted sample
(i.e., 50 ml chloroform [ml])
Multiplier:
(usually 1.000) this factor is used to include the influence of certain sample
components as well as mixed solvents (Losses or beyond results – can be determined by
titrating a standard solution or by adding a standard solution)
In the following (Fig. 2), a typical gradient is shown for the model substance 1-octen.
Fig. 2 Bromine number determination of 1-octen using the AQUA 40.00.
One can see that the reaction of the sample contents with the available bromine in the
measuring cell immediately takes place. An equivalent amount of bromine is generated from
the solved bromide at the anode. The used charge is registered and then calculated as
bromine number.
By using this method, different metered volumes were reproducibly determinated (Fig. 3).
A high reproducibility is achieved for the micro-coulometrical determination of the bromine
number, or alternatively, the bromine index (Fig. 4).
The Karl Fischer titrator AQUA 40.00 can be used for this determination without technical
adjustments.
Within a very short period of time, it is possible to alternately determine the water contents as
well as the bromine number, or alternatively, the bromine index, using the same apparatus
by only switching the used measuring cell.
The comfortable pc control software AQUA 40.00 allows various possibilities for comparison
and further interpretation of results.
3/5
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, Internet: http://www.ech.de, E-Mail: [email protected]
05 / 2004
KF_01_04_e
Fig. 3 The double-determination of the bromine number in one sample dissolvent with different metered volumes.
Fig. 4 Overview of results of determination of the bromine number in one sample dissolvent with different metered volumes.
4/5
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, Internet: http://www.ech.de, E-Mail: [email protected]
05 / 2004
KF_01_04_e
Procedure
Method for determination of the bromine number using the AQUA 40.00
1. Fill the measuring cell with electrolytes for the determination of the bromine number
(up to the lower edge of the glass cylinder with the septum lid, approx. 150 ml)
2. Fill the bubble counter half full with water – as a water seal; attatch it to the fitting
socket of the anode compartment
3. Put the measuring cell with the diaphragm and watery solution on the AQUA 40.00
4. Connect the electrodes to the electrode cables according to their color markings
Attention!
No traces of iodine may access the electrolytes!
Therefore, never use the electrodes or stirring apparatus of the measuring cell for
determining water according to Karl Fischer for the determination of the bromine number!
5.
6.
7.
8.
Turn on the AQUA 40.00
Start the computer
Load the apparatus software
Choose „bromine number“ in the first dialog window
Different apparatus parameters pertaining to the determination of the bromine number are
now loaded, including the method of measurement (F6) as well as the formula for the
calculation of results.
The method of measurement can be individually changed:
It is recommended to save the data file to a desired path determined by the user.
The formula used for the determination of the bromine number can also be edited in
the formula administration program or even new formulas may be added. These must
then be chosen in the dialog window “method of measurement”.
Changes in the method of measurement apply to all following measurements.
It is recommended to exchange the electrolytic solution on a daily basis before beginning
measurement. If using the components methanol, potassium bromide and/or glacial acetic
acid, these should first be made directly before being filled into the measuring cell. The
standard (cyclohexene, 1-Octen) should also be made daily, in order to avoid losses due to
volatility.
5/5
Developed by: ECH Elektrochemie Halle GmbH, Weinbergweg 23, D-06120 Halle/S.
Telefon: 0345/5583-711, Telefax: 0345/5583-710, Internet: http://www.ech.de, E-Mail: [email protected]