Metrohm 797 VA Computrace User Manual

Page 63

3.2 VA measurement modes

797 VA Computrace – Software

Sweep parameters:

Hydrodynamic (measurement) [ on, off ; off ]

Enable/disable stirring of the RDE/SSE during the sweep.

Potential limit (V)

[ -5...+5 V ; -0.2 V ]

Voltage limit for PSA sweep.

Maximum time (s)

[ > 0 ; 20 s ]

Time limit for PSA sweep.

Notes:
• The PSA measurement mode should only be used with RDE

electrodes (mainly with Hg film).

CCPSA – Constant Current Potentiometric Stripping Analysis

General:
CCPSA

Constant Current Potentiometric stripping

analysis

with oxidation by an applied constant current is mainly

used to determine substances in an organic matrix with the aid of
mercury film electrodes without prior digestion. The CCPSA measu-
rement mode can be set for the exploratory and determination mo-
de by selecting

CCPSA – Constant Current Potentiometric stripping

analysis

for the

Mode

parameter in the

EXPLORATORY SPECIFICA-

TION

WORKING METHOD SPECIFICATIONS

window.

Description:

In CCPSA measurement mode, the analytes are deposited at the
working electrode with the constant

Deposition potential

during a

predetermined

Deposition time

. Then the applied deposition poten-

tial is switched off and a constant current is applied. 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

Po-

tential 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

characteristic of the substance, the

Peak area

is proportional to its

concentration.