Malvern MPT-2, User Manual, Page: 31 / 85

Connection and accessory preparation Chapter 2
MPT-2 & Degasser Page 2-9
A note on titrant concentration
Preparing and specifying the concentration of the titrants is critical to achieving
accurate results. The concentration specified within the
Titrants SOP dialogue
must be accurate to within 10%.
A concentration of 0.25M is satisfactory for most measurements. In some situations
it may be wise to vary this. For example, if a large number of points is to be used in
a titration measurement, or if performing pH measurements close to pH 7, a lower
concentration may be needed.
The titrator can accurately dispense small volumes so concentrations of titrant up
to 1M can be used.
It is recommended that pre-diluted titrants are purchased. Either use titrants that
are diluted to the exact concentration required, or purchase titrants of a known
Molar concentration that can be easily diluted further.
For titrations that cover a wide pH range it is useful to use two concentrations of
titrant, e.g. 0.25M of acid and 0.01M of the same acid. This will ensure that the pH
values achieved are closer to the requested values.
Priming
Caution!
DO NOT prime the membranes by pushing titrant through the degassing
systems. This technique can generate several hundred pounds of pressure
which might rupture the Teflon AF® membrane. The maximum recom-
mended pressure on the membrane is
0.7 MPa ( 100 psig, 7 Bar ).
Priming is the process of ensuring that all the titrant delivery tubes are free of air
and full of liquid. Generally this is done after changing titrants or after the system
has not been used for a time, e.g. overnight.
Over time, the titrant may evaporate from the end of the titrant tube and therefore
it will not deliver the correct volume when first used. It is recommended that the
dispenser unit is primed every morning or at the beginning of a new session. Select
one prime cycle when performing a daily prime.
The dispenser unit should also be primed when a titrant container is changed in
order to remove any traces of the original titrant that may be left in the titrant tubes.
Three prime cycles will be sufficient to remove previous titrant.
Each titrant delivery tube can be individually primed, or all tubes can be primed
simultaneously. The coloured indicators on the dialogue match the LED indicators
next to the titrant container, and also the titrant tubing connectors.
MAN0318-4.0 - MPT-2 Autotitrator-Degasser.book Page 9 Tuesday, September 4, 2012 12:15 PM