Potentiometric Determination of the Cationic Surfactants in Fabric softener

Potentiometric Determination of the Cationic Surfactants in Fabric Softener


Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0507.120 Ionic surfactant electrode; input 1
6.0733.100 Ag/AgCl reference electrode (c(KCl) = 3 mol/L)

Reagents
c(DOS) = 0.01 mol/L; D0
Dioctylsodium sulfosuccinat M(DOS) = 444.57 g/mol, Fluka No. 86139

Sample
app. 1 g sample (fabric softener)
5 mL Methanol puriss p.a.
5 mL Buffer solution pH = 3, citrate/HCl, e.g. Merck Titrisol No. 9883
1 mL c(HCl) = 2 mol/L
60 mL dist. water

Remarks
Calculations:

Cationic=EP1*C01/C00;4;meq/g

Cationic = concentration of cationic surfactants in meq/g
C01 = concentration of titrating agent (0.01 mol/L)

Answer

Cationic = 12.631 x 0.01 / 1.0631 = 0.1188 meq/g

EP1 = 12.631 mL
C00 = 1.0631 g

Electrode preparation, maintenance and storage:
Store the Ionic Surfactant electrode dry. They are conditioned by two to three titrations. Rinse the electrode after several titrations with methanol or wipe it with a cloth moistend woth methanol and rinse with dist. water. If you use the electrode frequently, it may also be stored in a solution of 1% polyethyleneglycol 1000. In this case, the electrode is always ready to use.

Sample preparation:
Adjust the sample size in order to have a titrating agent consumption of at least 10 mL.
The pH of buffer solution, the amount of added methanol or the titrating agent may change according to the type of surfactant. See also Application Bulletin No. 233.

Literature
Metrohm Application Bulletin No. 233: Titrimetric / potentiometric determination of anionic and cationic detergents with the high-sense
surfactant electrode.

Method documentation
'pa
751 GPD Titrino 15215 751.0010
DET U Tens.Cat
parameters
>titration parameters
meas.pt.density 3
min.incr. ...10.0 ml
dos.rate max…. ml/min
signal drift …OFF mV/min
equilibr.time ….10 s
start V: ….OFF
pause ….30 s
dos.element:… internal D0
meas.input: …1
temperature …25.0 °C
>stop conditions
stop V: …abs.
stop V …20 ml
stop U …OFF mV
stop EP …9
filling rate max…. ml/min
>statistics
status: ….OFF
>evaluation
EPC …5
EP recognition: greatest
fix EP1 at U… OFF mV
pK/HNP: …OFF
>preselections
req.ident: …OFF
req.smpl size:… value
activate pulse: …OFF
------------
'fm
751 GPD Titrino 15215 751.0010
DET U Tens.Cat
>calculations
Cationic=EP1*C01/C00;4;meq/g
C00= 1.0631
C01= 0.01
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) 300 mV DET U Tens.Cat
smpl size 1.0631 g
EP1 12.631 ml 157 mV
Cationic 0.1188 meq/g
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U Tens.Cat