HIRANUMA APPLICATION DATA

Watercontents

Karl Fischer Titrator

Data No. KF15

Nov.29.
2018

Ketones – KF Coulometry, Direct-Injection
Methyl ethyl ketone and Acetone

1. Abstract
Water content of ketones could be 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・HSO4CH32RN・HI → I2 ＋ 2RN ＋ 2H＋ ＋ 2e－When the sample is liquid, generally sample is measured by direct injection into the titration cell. Anodesolution containing methanol as solvent is generally used for various sample. However, in the measurement ofketones and aldehydes, since these react with methanol to produce water, the measurement result tends to behigher than the true value (formula (1)).
R2CO+2CH3OH →R2C(OCH3)2+H2 O・・・(1)For above reason, Karl Fischer reagent without methanol should be used for water determination of ketonesand aldehydes.

There are commercially available reagents with a special composition for ketones andaldehydes. This chapter introduces an example for the water determination in methyl ethyl ketone and acetone.
These samples are often used as paint solvents, raw materials of adhesives, and synthetic resins.

2. Apparatus and Reagents(1) Apparatus
Titrator：

Hiranuma Karl Fischer Coulometric titrator

Electrolytic cell：Standard Cell

AQ-series

Fritless Cell (No cathode solution required)(2) Reagents
Anode solution：

HYDRANAL Coulomat AK (for ketone, Honeywell)

Cathode solution：

HYDRANAL Coulomat CG-K (for ketone, Honeywell)

3. Procedure(1) Fill 100 mL of anode solution and one ampoule of cathode solution into the electrolytic cell as shownin Fig.3.1. When fritless cell is used, cathode solution is not necessary.
(2) Start blanking to attain stable background.
(3) Wash the syringe with sample.
(4) Draw the sample into syringe and then weigh the syringe.
(5) Inject sample from rubber septum of electrolytic cell as shown in Fig.3.2.
(6) Start titration. Measurement parameter is shown in Table 4.1.
(7) Weigh the syringe again and then set the difference of weight to sample size.

Cathode solution

Anode solution

Fig.3.1. Preparation of the reagents. (Standard Cell)
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.

4. Parameters and results
Table 4.1. Parameters
Condition File
Cal ModeInterval Time
Current
S.Timer
Blank Value
Unit Mode
Auto Interval
Minimum Count
Back Ground
Sample Size Input
Cell Type0:Sample weight (net)
X=(H2O-BLANK)/SIZE30
SLOW00AUTO
05ON
Every Time
Standard / Fritless

secminµggµg

Table 4.2. Results of water content measurement in ketones.
SampleCellSample
Size (g)Water(μg)

Water content(ppm)

Methyl ethyl ketone

Standard0.4565

103.8

227.4

Avg.

223.9

ppm

0.4722

107.7

228.1

SD

6.7

ppm

0.4478

96.8

216.2

RSD

3.0%

0.4346

92.3

212.4

Avg.

209.3

ppm

0.4596

93.7

203.9

SD4.7

ppm

0.2856

60.4

211.5

RSD

2.2%

0.4515

102.6

227.2

Avg.

225.3

ppm

0.6059136.0

224.5

SD

1.7

ppm

0.4945

110.8

224.1

RSD

0.7%

0.4535

100.8

222.3

Avg.

223.6

ppm

0.5513

124.1

225.1

SD

1.4ppm0.3330

74.4

223.4

RSD

0.6%

FritlessAcetoneStandard

Fritless

Statistics result

5. Note(1) When the side reaction cannot be suppressed even though you use reagent for ketons, phenomena
such as unstable blanking or undetectable endpoint can be obtained. In that case, it may be improvedby reducing the amount of sample or replacing titration solvent with new one.
(2) Sample with high activity side reaction like cyclohexanone cannot be measured by coulometry –direct injection method. Since the boiling point of cyclohexanone is much higher than that of water andtoluene, it can be measured by suppressing the influence of side reaction with coulometry - azeotropic
distillation method (Refer to Application Data No. 16.)
(3) The optimized electrolysis control for fritless cell of AQ series released after 2009 improves themeasurement accuracy of fritless cell. It can be used with the evaporator as well. Suitable reagent for
fritless cell is required. For example, Hydranal coulomat AG and AG-Oven are compatible with fritlesscell.
Hydranal coulomat AK is a reagent designed to be used in standard type cell with diaphragm. Whenused in a fritless cell, it is sait to have an error of a few % with respect to the result with standard cell.
Results measured with fritless cell and coulomat AK are shown in the Table 4.2 as reference values.
Keywords：Karl Fischer, Coulometric titration, Direct injection, Ketone, Fritless cell