Metrohm 835 Titrando - Manual (Page 36)

2.6 Sensor connection
30
Titrando Installation Instructions
2.6.2 Differential potentiometry
During potentiometric measurements in poorly conducting media, high-
impedance measuring sensors are affected by electrostatic and elec-
tromagnetic interferences. Use our Solvotrode 6.0229.100 or any other
special electrode for pH measurements in organic solvents. If this does
not help then you can connect a Differential amplifier 6.5104.030
(230 V) or 6.5104.040 (115 V).
The Differential amplifier is connected to the high-impedance measur-
ing input (Ind.).
2.6.3 Titration vessel setup
In titration it is important that the solution is thoroughly mixed. The stir-
ring rate should be high enough for a small vortex to be formed. If the
stirring rate is too high then air bubbles will be entrained. This results in
incorrect measurements. If the stirring rate is too low then the solution
at the electrode will not be correctly mixed. To ensure that the meas-
urement is made in a thoroughly mixed solution after titrant addition the
buret tip should be located where the turbulence is greatest. In addi-
tion, the distance between the spot where the titrant is added and the
electrode should be as large as possible. When positioning the elec-
trode and buret tip you must also take the stirring direction into ac-
count.
1
2
3
Fig. 20: Recommended arrangement of magnetic stirring bar (1),
electrode (2) and buret tip (3)