BTG Mutek PCD-05 Smart, Руководство по эксплуатации

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14 Operation Manual Mütek
TM
PCD-05, September 2017 © BTG
II. Product description
2.1.3 Determination of the isoelectric point
Acid/ base titration
Apart from charge measurements, the Mütek™ PCD-05
lends itself to identifying the isoelectric point (IEP) of
dispersions.
The IEP is the pH-dependent point of zero charge of a
particle.
By adding a titrant (acid/ base) drop by drop, the
sample’s pH is shifted until the isoelectric point (strea-
ming potential = 0 mV) is reached.
Cationic samples are titrated with a base and anionic
samples with an acid up to the point of 0 mV.
Hint
The isoelectric point can only be identified with a
Mütek™ PCD-05 Smart or with a Mütek™ PCD-05 Light
in combination with an external titrator.
Fig. 2-2 Schematic of isoelectric point
2.1.4 Titrations curves
Information
The Mütek™ PCD-05 Smart continuously generates a
titration curve while performing a sample titration.
(Otherwise titration curve can only be obtained if the
Mütek™ PCD-05 is operated together with an external
titrator, the associated software and a printer.)
Titration curves are basically difficult to interpret,
because the curve progression does not exclusively
reflect the sample material, but rather the adsorption
behaviour of the sample at the surface of the measuring
cell. This is why the curve progression should not be
taken as a basis for the discussion of results. Instead,
under certain conditions, the curves provide information
about the nature of the sample under test. The titration
curves shown in the following may roughly be associa-
ted with different stock systems:
2.1.4.1 Colloidally dissolved particles
A titration curve obtained for a colloidally dissolved
sample is shown in Fig. 2-3.
At the onset of titration, the streaming potential remains
essentially unchanged, since the non-adsorbed colloids
are neutralized and do not therefore contribute toward
the generation of a streaming potential.
Later on, the streaming potential undergoes a sharp
drop, which is indicative of the fact that adsorbed
charge carriers are neutralized at the cell wall and pis-
ton.
Fig. 2-3 Colloidally dissolved particles
IEP