Metrohm 754 Dialysis Unit - Manual (Page 29)

3 Operation
754 Dialysis Unit
26
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Transfer time [min]
Concentration [mg/L]
Fluoride
Chloride
Nitrite
Bromide
Nitrate
Phosphate
Sulphate
3.3.5 Setting the dialysis time
After calculating the optimum transfer time, determine the optimum di-
alysis time. This value will depend on the total ion concentration. The
dialysis time with a stopped acceptor flow should be selected so that
100% of the sample concentration is achieved in the acceptor solution.
For the 6.2714.010 dialysis membrane (cellulose acetate; thick-
ness = 115 µ m; pore size = 0.2 µ m) available from Metrohm, the opti-
mum dialysis time for a total ion concentration of ≥ 5 mg/L is 10 min.
If a different dialysis membrane is used, or measurements are taken
with a total ion concentration of < 5 mg/L, then the optimum dialysis
time will have to be redetermined by measuring the recovery rate in re-
lation to time. Proceed as follows:
1 Measure the standard directly
• Switch off remote control of the 754 Dialysis Unit with the
key 22 (see section 3.1).
• Set the two valves A and B on the 733 IC Separation Center
to "FILL" with keys 23 23 and 25 25.
• Immerse suction tubing 27 27 in the required ion standard,
which has approximately the same total ion concentration as
the samples.
• Switch on the pump on the 754 Dialysis Unit with the
key 11.
• After approx. 2 min, switch valve A on the 733 IC Separation
Center to "INJECT" with key 24 24 and simultaneously start the
data evaluation system. In operation with the 753 Suppressor
Module, the suppressor has to be rotated with the
key.
• Immerse suction tubing 27 27 in the acceptor solution and rinse
the acceptor channel for approx. 2 min.
• Switch off the pump on the 754 Dialysis Unit with the
key 11.
• Switch the remote control of the 754 Dialysis Unit back on
with the key 22.