Metrohm 757 VA Computrace - Manual (Page 53)

3.2 VA measurement modes
757 VA Computrace – Software
43
AC – Alternating Current Voltammetry
General:
AC or Alternating Current voltammetry is primarly suitable for
reversible electrode reactions. It is virtually completely insensitive
to irreversible reactions. The AC measurement mode can be set
for the exploratory and determination mode by selecting
AC - Al-
ternating current voltammetry for the Mode parameter in the
EXPLORATORY SPECIFICATION or WORKING METHOD
SPECIFICATIONS window.
Description:
For AC voltammetry, a digitally generated sinusoidal alternating
voltage with a small, constant amplitude and a low frequency is
superimposed on a stepwise rising direct voltage ramp. The first
or second harmonic wave of the alternating current component
i
produced by the alternating voltage is measured as a function of
the voltage
U. The current measurements give peak-shaped
(AC1) or sinusoidal shaped (AC2) curves which can be evaluated
using linear, polynomial or exponential baselines.
U
t
× √ 2 Amplitude
1 / Frequency 1 / Frequency
Phase angle
i
U
i = Σ ( i+ ) / n
Peak voltage
Peak
height
i
U
i = Σ ( i+ - i- ) / n
Half-wave voltage
AC1 AC2
Voltage step
Modulation time
Voltage step time
U
i
i+
Phase angle
U
i
i+ i-