Metrohm 828 IC Dual Suppressor - Manual (Page 31)

3.2 Eluent
828 IC Dual Suppressor/ 8.828.1003 Instructions for Use
23
3.2 Eluent
The cation exchanger resin of the 828 IC Dual Suppressor allows the
use of all the eluents normally used for suppressed ion
chromatography such as hydroxide, borate and carbonate/bicarbonate
eluents, although carbonate/bicarbonate eluents offer the greatest
benefits when used with the 828 IC Dual Suppressor because of the
removal of CO
2
.
In order to achieve the best results you should only use ultrapure
reagents and ultrapure water to prepare your eluents .
3.3 Capacity
The exchange capacity of the suppressor cell of the 828 IC Dual
Suppressor is 50 mmol/L NaOH or 25 mmol/L Na
2
CO
3
at a flow rate of
1 mL/min.
Check whether the concentration of your eluent and the selected flow
rate are appropriate for the capacity of the suppressor before you start
to use it.
Calculate the maximum "Total cation flow" for your eluent or gradient
and your flow rate in milli-equivalents of cations that pass through the
cell per minute (meq/min). The total amount of 0.05 meq/min must not
be exceeded.
Example
An eluent with 5 mmol/L Na
2
CO
3
/5 mmol/L NaHCO
3
and a flow rate of
1.5 mL/min gives a value of 0.0225 meq/min for the total cation flow
and is therefore within the capacity of the suppressor cell.
3.4 Degassing unit and CO
2
absorber cartridge
A further improvement of the signal from the 828 IC Dual Suppressor is
achieved with carbonate/bicarbonate eluents by degassing the
suppressor eluate before detection. Dissolved CO
2
is removed from the
suppressor eluate with the result that the background conductivity is
reduced, the signal-to-noise ratio is improved, the injection peak (water
dip) and system peak are eliminated and the rise in the background
conductivity with carbonate/bicarbonate gradients is suppressed.
The degassing unit consists of a vacuum pump, a vacuum chamber
and a CO
2
absorber cartridge. In the vacuum chamber carbonic acid
dissociates to form water and carbon dioxide. In order to prevent the
formation of an equilibrium between the dissolved and gaseous CO
2
in
the vacuum chamber, the vacuum pump works with a gas ballast. A
small amount of ambient air is drawn in by the pump and passes
through the vacuum chamber so that any CO
2
evolved is continuously