24
Operation Manual Mütek
TM
PCD-05, September 2017
© BTG
IV. Installation
4.4.3
Sample specification
General
Basically, nearly every aqueous sample - including ori-
ginal concentrations - can be measured. The measura-
bility of a sample may be verified by the Mütek™ PCD-
05 Particle Charge Detector. To this end, fill a sample
into the measuring cell, install the cell together with the
displacement piston in the Mütek™ PCD-05 and turn on
the motor. Measurement may be started as soon as the
motor runs smoothly and silently and the signal keeps
comparatively stable (at approximately ±50 mV).
The limit values indicated in this chapter are not abso-
lute values, but are merely indicative of sample cha-
racteristics that might lead to measuring problems.
If there are doubts about whether or not a substance
can be measured, conduct a test measurement and, if
necessary, condition the sample accordingly.
Solvents
Charge measurement is possible after functional groups
are dissociated. Since this dissociation can only take
place in aqueous solutions, the substance to be tested
must be available in this form or be dispersed in water.
If required, the substance to be tested may be dissolved
in lower alcohols (methanol, ethanol, isopro-panol)
before it is diluted with de-ionized water for subsequent
titration.
The proportion of organic solvents depends on the
sample and should be determined in pretests. To begin
with, a blank reading should be obtained for the solvent
concerned. For this purpose, fill 10 ml of the solvent
(de-ionized water or a water/ alcohol mixture) into the
measuring cell and titrate up to the point of zero charge.
Even if the cell is filled with de-ionized water only, the
streaming potential will not be at 0 mV as might be
expected, but will show a comparatively high anionic
signal. This signal drops to zero as soon as a minimum
amount of a cationic titrant is added.
If de-ionized water is titrated, approximately 0.02 ml
Poly-Dadmac is normally required.
The blank value thus obtained is to be deducted from
the results of all further titrations.
Particle sizes
Solid particle sizes in a sample should not exceed 500
µm. The minimum detectable limit value is 1 nm.
Viscosity
Suitable for measurement are all samples with a visco-
sity below 6000 mPa*s. Viscosities exceeding this value
impede the oscillating movement of the displacement
piston in the measuring cell. This restriction is still
aggravated by the flocculation effect typically occurring
toward the end of titration.
Accordingly, samples with a viscosity exceeding 6000
mPa*s should conveniently be diluted with de-ionized
water.
If highly viscous samples are to be titrated, mixing the
titrant with the sample takes longer than with low-visco-
sity samples.
Molecular weight
The minimum molecular weight of polyelectrolytes to be
tested should be at approximately 300 g/mol, since with
smaller molecules, their adsorption on the cell wall by
van-der-Waal forces is no longer ensured. Ions present
in a sample due to dissolved inorganic salts are below
the detection limit.
At the upper end of the scale, there is no limiting mole-
cular weight of colloidally dissolved substances.
