BTG Mutek PCD-05 Smart, Руководство по эксплуатации

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36 Operation Manual Mütek
TM
PCD-05, September 2017 © BTG
V. Measuring
5.7.4 Back titration
This method of sample preparation suggests itself in the
following cases:
- Due to their structure, the samples cannot be trans-
ferred to the cell directly which would enable quanti-
tative determination of the charge level of larger
particles
- The reaction of the substance to be tested with the
titrant is too slow for direct titration
5.7.4.1 Example for back titration
Sample
The total charge of an anionic solid sample is to be
determined. In view of the high solids content or exces-
sive particle sizes, direct measurement in the measu-
ring cell is not feasible. Instead, back titration is
recommended.
Procedure
Take 20 g of the anionic sample to be measured and fill
up to 100 g with Poly-Dadmac 0.001 N. Stir this mixture
for approximately 2 hours with a magnetic stirrer. During
this period, the cationic Poly-Dadmac will neutralize all
anionic charges of the sample. Since there is an excess
amount of Poly-Dadmac, a residual cationic charge will
remain in the sample.
After the reaction period, remove the solids from the
mixture by screening. Pipette 10 ml of the solution into
the measuring cell and titrate up to the point of zero
charge with Pes-Na 0.001 N.
Result V1: Consumed Pes-Na 4.83 ml
In addition, titrate 10 ml of fresh Poly-Dadmac solution
with Pes-Na up to the point of zero charge.
Result V2: Consumed Pes-Na 10.68 ml
Calculation of charge density q:
V2 - V1: The difference between the charges of
the fresh Poly-Dadmac and the reacted
Poly-Dadmac indicates the charge
amount neutralized in the sample.
c: Concentration of the titrant,
here 0.001 eq/l
m: 2 g of the original sample were used for
titration. (20 g were filled up to 100 g of
which 10 g were used for titration.)
Result: The charge of the sample under test is
2.925 µeq/g.
(V2 - V1) * c
m
q =
(0.01068 - 0.00483) [l] * 0.001 [eq/l]
q =
2 [g]
q = 2.925 * 10
-6
[eq/g]