Metrohm 797 VA Computrace - Manual (Page 62)

3 General settings for exploratory and determination mode
797 VA Computrace – Software
50
PSA – Potentiometric Stripping Analysis
General:
PSA or Potentiometric stripping analysis with chemical oxi-
dation is mainly used to determine substances in an organic matrix
with the aid of mercury film electrodes without prior digestion. The
PSA measurement mode can be set for the exploratory and deter-
mination mode by selecting
PSA - Potentiometric stripping analysis
for the Mode parameter in the EXPLORATORY SPECIFICATION or
WORKING METHOD SPECIFICATIONS window.
Description:
In PSA measurement mode, the analytes are deposited at the work-
ing electrode with the constant
Deposition potential during a pre-
determined Deposition time . Then the applied deposition potential
is switched off and the voltage U is measured as a function of the
time t with a sampling rate of
69.69 kHz. The measurement time is
limited either by the set Potential limit or the Maximum time . The
voltage measurement U vs t is used to calculate the retention times
dt/dU vs U. This results in peak-shaped curves which can be evalu-
ated. The
Peak voltage is characteristic of the substance, the Peak
area is proportional to its concentration.
U
t
Deposition potential
Deposition time
Potential limit
Maximum time
dt/dU
U Peak voltage
Peak
area