Karl Fischer Titrator

HIRANUMA APPLICATION DATA

Watercontents

Data No. KF16

Apr. 19,2018

Ketones, Cyclohexanone – KF Coulometry,Cooled direct injection, Azeotropic distillation

1. Abstract
Water content of cyclohexanone is determined by Karl Fischer coulometric titrator. In coulometric titration,
iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water.
Reaction formula is described below.
H2O ＋ I2 ＋ SO2 ＋ 3RN ＋ CH3OH → 2RN・HI ＋ RN・HSO4CH3
2RN・HI → I2 ＋ 2RN ＋ 2H＋ ＋ 2e－Ketones and aldehydes would interfere the Karl Fischer reaction by side-reaction with methanol (formula (1)).
R2CO+2CH3OH →R2C(OCH3)2+H2 O・・・(1)Therefore it is necessary to use methanol-free anode and cathode solution. There are commercially available
reagents with a special composition for ketones and aldehydes. However, cyclohexanone has particularly astrong side reaction activity, so it is difficult to measure by direct injection method at room temperature. In themeasurement of cyclohexanone, it is effective to lower the activity of side reaction by cooling or to separate
cyclohexanone and water by distillation.
This application introduces an example for the water determination in cyclohexanone with cooled direct
injection method and azeotropic distillation method.

2. Apparatus and Reagents(1) Apparatus for cooled direct injection method
Titrator：

Hiranuma Karl Fischer Coulometric titrator

AQ-series

Electrolytic cell：

Electrolytic cell w/cooling chamber

P/N : D327326-1(2) Apparatus for azeotropic distillation method
Titrator：

Hiranuma Karl Fischer Coulometric titrator

AQ-series

Evaporator：Hiranuma Oil Evaporator

EV-2000L

Electrolytic cell：Standard Cell

Anode solution：

HYDRANAL coulomat AK (for ketone, Honeywell)

Cathode solution：

HYDRANAL coulomat CG-K (for ketone, Honeywell)

Distillation solvent：

Dehydrated toluene

Carrier gas：

Nitrogen gas(3) Reagents

3. Procedure
3.1. Cooled direct injection method(1) Fill 100 mL of anode solution and one ampoule of cathode solution into the electrolytic cell as shownin Fig.3.1.
(2) Cool the inside of the cell by circulating 5 °C cold water in the cooling chamber and wait until thetemperature stabilizes.
(3) Start blanking to attain stable background.
(4) Wash the syringe with sample.
(5) Draw the sample into syringe and then weigh the syringe.
(6) Inject sample from rubber septum of electrolytic cell as shown in Fig.3.2.
(7) Start titration. Measurement parameter is shown in Table 4.1.
(8) Weigh the syringe again and then set the difference of weight to sample size.
Anode solution

Cathode solution

Fig.3.1. Preparation of the reagents.
Note(1) Do not touch the tip of needle to anodesolution.
(2) When injecting, set the tip of needle as
below figure.

(3) Before pulling out the needle, draw alittle air to prevent dripping of sample.

Fig.3.2. Injection of sample.

3.2. Azeotropic distillation method(1) Fill 100 mL of anode solution and one ampoule of cathode solution into the electrolytic cell as shownin Fig.3.1.
(2) Start blanking to attain stable background.
(3) Connect electrolytic cell and evaporation chamber with tube. Flow carrier gas with 50 mL/min.
(4) Fill 5 mL of distillation solvent in evaporation chamber and heat the chamber at 120 C.
(5) Keep blanking to attain stable background with carrier gas flowing into electrolytic cell.
(6) Wash the syringe with sample.
(7) Draw the sample into syringe and then weigh the syringe.
(8) Inject sample from rubber septum of distillation chamber as shown in Fig.3.3 and Fig.3.4.
(9) Start titration. Measurement parameter is shown in Table 4.2.
(10) Weigh the syringe again and then set the difference of weight to sample size.

Fig.3.3. Schematic diagram of azeotropic distillation method.
Note(1) Do not touch the tip of needle to distillationsolvent level.
(2) When injecting, set the tip of needle as below
figure.

(3) If air is drawn at inside of evaporation chamber,distillation solvent would be involved. Whendrawing air, do it after pulling out the needle
from evaporation chamber to prevent weighing
error.

Fig.3.4. Sample injection into evaporation chamber.

4. Parameters and results
Table 4.1 Parameters for cooled direct injection method
Condition File
Cal ModeInterval Time
Current
S.TimerBlank Value
Unit Mode
Auto Interval
Minimum Count
Back GroundSample Size Input
Cell Type

Table 4.2 Parameters for azeotropic distillation method
Condition File
Cal Mode

0:Sample weight (net)
X=(H2O-BLANK)/SIZE
20 sec
SLOW0 min0 μg
AUTO0 g
5 μg
ONEvery Time
Standard

Interval TimeCurrent
S.Timer
Blank Value
Unit Mode
Auto Interval
Minimum Count
Back Ground
Sample Size Input
Cell Type

0:Sample weight (net)
X=(H2O-BLANK)/SIZE
40 sec
SLOW0 min0 μg
AUTO0 g
5 μg
ONEvery Time
Standard

Table 4.3 Results of water content measurement in cyclohexanone
MethodSamplesize (g)Water(μg)

Cooled direct injection

0.269255.1

204.70.2581

62.6

242.5

0.2711

61.6

227.2

1.3661

300.2

219.7

1.5261

338.9

222.1

1.5824

348.6

220.3

Azeotropic distillation

Water content(ppm)

Statistics result

Avg. 224.8 ppm
19.0 ppm
SD8.5 %RSD
Avg. 220.7 ppm
1.2 ppm
SD
0.5 %
RSD

5. Note(1) Azeotropic distillation method achieved better results with repetition accuracy than the cooled direct
injection method. Since the boiling point of cyclohexanone was 155 °C higher than water and toluene,
it seems that water could be separated well from cyclohexanone by distillation. The distillation method
can also be applied to paints containing resins and lubricants containing additives.
(2) When substances that cause side reactions flow out from the distillation chamber into the cell, thebackground gets unstable or high. In that case, it may be improved by reducing the amount of sample
or replacing titration solvent with new one.
Keywords：Karl Fischer, Coulometric titration, Cooled direct injection, Azeotropic distillation, Ketone