Standardization of benzethonium chloride standard solution | Autotitrator COM-A19
HIRANUMA APPLICATION DATA Automatic Titrator Data No. C11 Jun.30,2020
Detergents・Bath additives・Cosmetics Standardization of benzethonium chloride standard solution

1.Abstract

The determination method of anion surfactant uses a cation surfactant, with an opposite charge, as the titrant. 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, and standardize the benzethonium chloride standard solution with titration against sodium dodecyl sulfate standard solution.

2. Configuration of instruments and reagents

(1) Configuration of instruments    
    Main unit : Hiranuma Automatic Titrator COM Series
    Electrode : Glass reference combination electrode   GR-525BZ
  (Used to measure the purity of sodium dodecyl sulfate)
Surfactant electrode   SU-091
Reference electrode  RE-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
i) Take 5 g of sample into a 300 mL Erlenmeyer flask and accurately weigh it.
ii) Add 25 mL of 0.5 mol/L sulfuric acid with a volumetric pipette.
iii) 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.
vi) 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.
v) Immerse electrode (GR-525BZ) and start titration with 1 mol/L sodium hydroxide standard solution.
iv) 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
i) Take 10 mL of sodium dodecyl sulfate standard solution into a 100 mL beaker with a volumetric pipette.
ii) Add 50 mL of DI water.
iii) Immerse electrode (SU-091, RE-201Z) and start titration with 0.004 mol/L benzethonium chloride standard solution.

 

4. Measurement conditions and results

Examples of titration conditions

Titration condition for purity of sodium dodecyl sulfate (blank measurement)

Titration condition for purity of sodium dodecyl sulfate (blank measurement)

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

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

Titration condition for standardization of benzethonium chloride standard solution

Titration condition for standardization of benzethonium chloride standard solution

*1 Set calculated result of factor for sodium dodecyl sulfate in Section 4.2.

Measurement results

4.1. Measurement results for purity of sodium dodecyl sulfate

Item Meas.No. Size(g) Titrant volume
(mL)
Purity(%) Average
Blank 1 25.444 25.436 mL
2 25.427
           
Purity 1 5.5582 44.462 98.813 98.780 %
2 5.2842 43.512 98.747
           
 

4.2. 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. Size(mL) Titrant volume
(mL)
Factor Statistical results
1 10 10.289 0.9602 Avg: 0.9595
2 10.305 0.9587 SD: 0.00075
3 10.295 0.9596 RSD: 0.079 %
           

Examples of titration curve

 

Purity of sodium dodecyl sulfate
Blank

Purity of sodium dodecyl sulfate
Sample

Standardization of benzethonium chloride standard solution

5.Note

(1) Electrode
The 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 were able 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.

Detergents | bath additives | cosmeticsHiranuma aquacounter autotitrator com-a19

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