Metrohm 797 VA Computrace - Manual (Page 65)

3.2 VA measurement modes
797 VA Computrace – Software
53
AC – Alternating Current Voltammetry
General:
AC or Alternating Current voltammetry is primarily suitable
for reversible electrode reactions. It is virtually completely insensi-
tive 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 EX-
PLORATORY SPECIFICATION or WORKING METHOD SPECIFICA-
TIONS 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 pro-
duced 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
lin-
ear, polynomial, horizontal 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-