© BTG
Operation Manual Mütek
TM
PCD-05, September 2017
25
IV. Installation
Conductivity
The conductivity of a sample decisively impacts the
streaming potential: the higher the conductivity, the
lower the electrical resistance in the sample will be and
the more the streaming potential will decrease without,
however, influencing the titration results.
Fig. 4-1
Conductivity vs. streaming potential
In Fig. 4-1, various different NaCl proportions were
added to Pes-Na 0.001 N and the samples were titrated
with Poly-Dadmac 0.001 N.
Hint
If conductivities are excessively high (20 mS/cm - 50
mS/cm), the streaming potential may fluctuate be-tween
anionic and cationic so than an endpoint detection and
thus titration is no longer possible. In these cases,
reduce the conductivity by diluting the sample with de-
ionized water.
Information
Samples that do not meet the above specifications may
be prepared as outlined in chapter 5.7 "Sample prepa-
ration", page 35.
4.5 Solutions
4.5.1
Titrants
Titrants must always carry the opposite charge of the
sample.
The sample concentration (dilution) should optimally be
selected to keep the titrant consumption between 0.2
and 10 ml.
Polyelectrolytes
BTG Instruments AB recommends the use of Pes-Na
and Poly-Dadmac as standard reagents, since their
charge densities are practically pH-independent.
Pes-Na
Pes-Na (sodium polyethylene sulfonate) is an anionic
polyelectrolyte serving as a calibrating substance to
determine the content of other titrants.
Poly-Dadmac
Poly-Dadmac (polydimethyl diallyl ammonium chloride)
is a cationic polyelectrolyte.
For technical reasons, the activity of Poly-Dadmac is
subject to minor variation between individual batches.
Before using a fresh solution, apply Pes-Na to conduct
a factor determination.
Consumption of Poly-Dadmac 0.001 N is usually bet-
ween 9.75 and 10.25 ml for 10 ml Pes-Na 0.001 N.
Other polyelectrolytes
The following additional titrants are in frequent use
today:
Cationic:
- Methyl glycol chitosan (MGCh) 'Hymin'
Anionic:
- Potassium polyvinyl sulphate (PVSK)
- Sodium dodecyl sulfate (SDS)
Information
For the Mütek™ PCD-05, BTG Instruments AB supplies
titrant bottles containing Poly-Dadmac, Pes-Na and
PVSK in the concentrations 0.001 N and 0.0001 N.
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