Metrohm 757 VA Computrace - Manual (Page 51)

3.2 VA measurement modes
757 VA Computrace – Software
41
PSA – Potentiometric Stripping Analysis
General:
PSA or Potentiometric stripping analysis with chemical oxida-
tion 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 de-
termination mode by selecting
PSA - Potentiometric stripping analy-
sis for the Mode parameter in the EXPLORATORY SPECIFICATION or
WORKING METHOD SPECIFICATIONS window.
Description:
In PSA measurement mode, the analytes are deposited at the
working electrode with the constant
Deposition potential during a
predetermined Deposition time . Then the applied deposition po-
tential is switched off and the voltage U is measured as a function
of the time t with a sampling rate of 21.39 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 evaluated. 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