HIRANUMA APPLICATION DATA

Detergents・Bath additives・Cosmetics

Automatic Titrator

Data No. C11Jun. 30,
2020

Standardization of benzethonium
chloride standard solution

1. Abstract
The determination method of anion surfactant uses a cation surfactant, with an opposite charge, as thetitrant. The end point is the point at which the charge becomes neutral due to the reaction between the anion
and the cation. Benzethonium chloride is used as the cation standard solution.
This report introduces a method for standardization of benzethonium chloride standard solution. Sodium
dodecyl sulfate is used for standard solution. First, determine the purity of sodium dodecyl sulfate. Add diluted
sulfuric acid to sodium dodecyl sulfate, heat to reflux, and then titrate with sodium hydroxide standard solution.
Subsequently, prepare the standard solution of sodium dodecyl sulfate whose purity has been determined, andstandardize the benzethonium chloride standard solution with titration against sodium dodecyl sulfate standardsolution.

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrodes:

Glass-reference combination electrodeGR-525BZ(Used to measure the purity of sodium dodecyl sulfate)
Surfactant electrodeSU-091

Reference electrodeRE-201Z(Used for the standardization of benzethonium chloride)(2) Reagents
Titrant:

0.004 mol/L Benzethonium chloride standard solution
Dissolve 0.896 g of benzethonium chloride in DI water and prepare
500 mL solution.

Standard solution :0.004 mol/L sodium dodecyl sulfate standard solution
Dissolve 1.154 g of sodium dodecyl sulfate in DI water and prepare
1 L solution.

Additive:

0.5 mol/L sulfuric acid

Titrant:

1 mol/L sodium hydroxide standard solution

Rinse solution:ethanol (purity: 99.5 %)3. Measurement procedure
3.1. Measurement for the purity of sodium dodecyl sulfate(1) Take 5 g of sample into a 300 mL Erlenmeyer flask and accurately weigh it.
(2) Add 25 mL of 0.5 mol/L sulfuric acid with a volumetric pipette.
(3) Attach a reflux condenser to the flask and heat it with using hot plate or sand bath. Occasionally, swirl
the flask gently while being careful not to foam. Reflux for an additional 2 hours after the solution
becomes clear and does not foam.
(4) Cool the flask to room temperature. Wash the inner wall of the reflux condenser with 30 mL of ethanol(99.5 %), and next with an appropriate amount of water. Detach the reflux condenser from the flask
and add pure water to make it to 100 mL.
(5) Immerse electrode (GR-525BZ) and start titration with 1 mol/L sodium hydroxide standard solution.
(6) Perform blank measurement without sample.
3.2. Calculation for the factor of sodium dodecyl sulfate standard solution
Calculate factor for prepared 0.004 mol/L sodium dodecyl sulfate solution with the following formula:F ＝ (S × (P / 100)) / (M × 0.004) ＝ (2.5 × S × P) / M
S: Weighing amount of sodium dodecyl sulfate (g)P: Purity of sodium dodecyl sulfate (%)
M: Molecular weight of sodium dodecyl sulfate (288.38)
3.3. Standardization of benzethonium chloride standard solution(1) Take 10 mL of sodium dodecyl sulfate standard solution into a 100 mL beaker with a volumetricpipette.
(2) Add 50 mL of DI water.
(3) Immerse electrode (SU-091, RE-201Z) and start titration with 0.004 mol/L benzethonium chloridestandard solution.

4. Measurement conditions and results
Example of titration condition
Titration condition for purity of sodium dodecyl sulfate (blank measurement)

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto
1
1pH
522
501000
0.3
30sec
mL
sec
mL
mL
mL

Constant No.
SizeBlank
Molarity
FactorKL
Unit
FormulaDigits

10 g
0 mL
1 mol/L
1.001
00Mode No.
Pre Int
Del KDel Sens
Int Time
Int Sens
Brt SpeedPulse

409033240sec
mVsec
mV

mL
D
3Titration condition for purity of sodium dodecyl sulfate (sample measurement)

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2Auto
1
1pH
530
5010000.340sec
mL
sec
mL
mL
mL

Constant No.
SizeBlank
Molarity
FactorKL
Unit
FormulaDigits

25.5582 g
25.436 mL
1 mol/L
1.001
288.380Mode No.
Pre Int
Del K
Del Sens
Int TimeInt Sens
Brt Speed
Pulse

409033240sec
mVsec
mV%(D-B)*K*F*M/(S*10)
3Titration condition for standardization of benzethonium chloride standard solution

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

3Auto
22mV
20
000100
0.3
20sec
mL
sec
mL
mL
mL

Constant No.
SizeBlank
Molarity
Factor ※1KL

310 mL0 mL
0.004 mol/L
0.987900UnitFormulaDigits

Fact1S/(D-B)*F3※1 Set calculated result of factor for sodium dodecyl sulfate in Section 4.2.

Mode No.
Pre Int
Del KDel Sens
Int TimeInt Sens
Brt SpeedPulse

805053240secmV
secmV

Measurement results
4.1. Measurement results for purity of sodium dodecyl sulfate
Item

Meas.
No.
1

Size (g)Titrant
volume (mL)－Blank2

25.444

Purity(%)

Average－25.436mL

98.780%25.42715.5582

44.46298.8132

5.284243.51298.747

Purity4.2. Calculated result for factor of sodium dodecyl sulfate standard solution
F ＝ (2.5 × 1.1536 × 98.780) / 288.38 ＝ 0.9879
4.3. Measurement results for standardization of benzethonium chloride standard solution
Meas.
No.

SizeTitrant(mL)

volume (mL)

12

103

FactorStatistical results

10.2890.9602Avg.：

0.959510.3050.9587SD：

0.00075

10.2950.9596RSD：

0.079 %Blank

SamplePurity of sodium dodecyl sulfate

Example of titration curveStandardization of benzethonium chloride standard solution

Example of titration curve

5. Note(1) ElectrodeThe glass reference combination electrode was used for the purity determination of sodium dodecyl sulfate,
and the surfactant electrode was used for standardization of benzethonium chloride. Both measurements wereable to obtain the clear inflection point on titration curve as endpoint, and it was possible to measure without
problems.

Keywords: Anionic surfactant, Surfactant electrode, Sodium dodecyl sulfate, Benzethonium chloride*Some measurement would not be possible depending on optional configuration of system.