The determination of the surfactant content plays an important role in many analytical applications - from wastewater analysis up to quality control in production processes.
A method that is still in widespread use is the so-called Epton titration according to ISO 2271.
In this manual titration the anionic surfactant is precipitated by a cationic surfactant in a two-phase mixture of water and chloroform.
The ion pair formed must be extracted into the solvent phase by vigorous shaking.
The titration endpoint is determined visually using a colour indicator.
This complicated method suffers from the following disadvantages: use of chloroform, a toxic solvent; long waiting period for phase separation; and inaccurate visual endpoint recognition.
The potentiometric two-phase titration according to DIN EN 14480 and DIN EN 14468 describes a simpler, faster and less hazardous determination method.
The surfactant solution is pipetted into a titration vessel, to which a two-phase mixture of water and methyl isobutyl ketone/ethanol 1:1 and an emulsifier are added.
The emulsion formed is titrated under vigorous stirring.
The determination of the equivalence point (EP) takes place potentiometrically using surfactant-sensitive electrodes.
In comparison with the Epton titration you profit from the following advantages: use of unproblematic solvents; short determination times; improved precision due to the computerised determination of the EP; can easily be automated.
The advantage of this technology is shown in a variety of applications involving the surfactant content determination of cosmetics and household products (hair conditioner, bath oil, washing powder) as well as technical products (industrial cleaners).
Instrumentation: 809 Titrando; 804 Ti Stand; 802 Stirrer; 800 Dosino.
Cationic surfactants in hair conditioner
Analyte: Cationic surfactants
Sample: Hair conditioner Bellherbal, Migros, Switzerland
Solvent: Approx 70 mL of water and 20 mL methyl-isobutyl-ketone/ethanol, (1/1, v/v)
Emulsifier: 0.2 mL TEGO add
Titrant: sodium dodecyl sulphate, 0.005 mol/L
Hydrochloric acid, 1.0 mol/L
pH: 2.5
Electrodes: Surfactrode Refill
Reference Electrode Ag/AgCl/3 mol/L KCl Unitrode
Titr Mode: DET U
Sample - EP(mL) - Surfactant content - Mean value (mmol/100 g sample) - SD - RSD (per cent)
1 - 6.35 - 7.45
2 - 4.40 - 7.38 - 7.40 - 0.05 - 0.68
3 - 7.33 - 1.36
Anionic surfactants in bath oil
Analyte: Anionic surfactants
Sample Bath oil (free sample) from Acapulco, Mexico
Solvent: Approx 70mL of water and 20mL methyl-isobutyl-ketone/ethanol, (1/1, v/v)
Emulsifier: 0 .2 mL TEGO add
Titrant: TEGOtrant A 100 (1,3-didecyl-2-methyl-imidazolium chloride), 0.005 mol/L
Sulfuric acid, 0.5 mol/L
pH: 3
Electrodes: Surfactrode Resistant
Reference Electrode Ag/AgCl/3 mol/L
KCl Unitrode
Titr Mode: D ET U
Sample - EP(mL) - Surfactant content - Mean value (mmol/100 g sample) - SD - RSD (per cent)
1 - 9.16 - 52.32
2 - 8.61 - 52.68 - 52.54 - 0.20 - 0.38
3 - 10.4 - 52.63
Anionic surfactants in washing powder
Analyte: Anionic surfactants
Sample: Total Concentre, Migros, Switzerland
Solvent: Approx 70mL of water and 20mL methyl-isobutyl-ketone/ethanol, (1/1, v/v)
Emulsifier: 0 .2 mL TEGO add
Titrant: Hyamine 1622 (benzethonium chloride), 0.005 mol/L
Hydrochloric acid, 1.0 mol/L pH 2
Electrodes: Surfactrode Refill
Reference Electrode Ag/AgCl/3 mol/L
KCl Unitrode
Titr Mode: D ET U
Sample - EP(mL) - Surfactant content - Mean value (mmol/100 g sample) - SD - RSD (per cent)
1 - 8.91 - 29.92
2 - 9.10 - 30.35 - 29.88 - 0.49 - 1.64
3 - 10.54 - 29.38
Anionic surfactants in industrial cleaner
Analyte: Anionic surfactants
Sample: Multi-Clean, Eurotech, Austria
Solvent: Approx 70mL of water and 20mL methyl-isobutyl-ketone/ethanol, (1/1, v/v)
Emulsifier: 0 .2mL TEGO add
Titrant: TEGOtrant A 100 (1,3-didecyl-2-methyl-imidazolium chloride), 0.005 mol/L
Sulfuric acid, 0.5 mol/L
pH: 3
Electrodes: Surfactrode Resistant
Reference Electrode Ag/AgCl/3 mol/L
KCl Unitrode
Titr Mode: D ET U
Sample - EP(mL) - Surfactant content - Mean value (mmol/100 g sample) - SD - RSD (per cent)
1 - 9.24 - 10.98
2 - 8.72 - 10.75 - 10.98 - 0.23 - 2.09
3 -6.89 - 11.21
