Antec Scientific ROXY Exceed, User Manual, Page: 69 / 126

Chapter 7 Optimization of working potential 69
C H A P T E R 7
Optimization of working potential
Introduction
A current - voltage (I/E) relationship, or voltammogram, characterizes the
REDOX behavior of an electrochemically active target compound. It gives
information on the optimum oxidation/reduction potential, which can be
used to improve the products formation (yield & selectivity) of electrochem-
ical reactions. There are several ways to obtain the I/E relationship using
the ROXY potentiostat:
A
hydrodynamic voltammogram can be acquired using an EC flow cell
and ROXY potentiostat coupled to an (U)HPLC system with MS. The volt-
ammogram is obtained in the DC mode by running several chromatograms
at different working potentials and measuring the EC current signal and
mass spectra. A hydrodynamic voltammogram has as an advantage that
the I/E relationship of all target compounds and the structure of the formed
reaction products can be obtained simultaneously in one set of experi-
ments (boundary condition: all target compounds and reaction products
should be sufficiently separated under the applied LC conditions).
A
scanning voltammogram is obtained in the so-called scan mode of the
ROXY Potentiostat: in the scan mode the cell potential is swept between
two pre-set values (E1 and E2) using a certain scan speed (in mV/s and
the current is measured during the sweep. This method can be used to
study the REDOX behavior of a pure target compound dissolved in a suita-
ble mobile phase.
Hydrodynamic and scanning voltammetry are common methods to obtain
the optimized potential for a target compound in EC/LC/MS or EC/MS
when a mass spectrometer is used as a detector. A MS Voltammogram
can be obtained also in DC mode by ramping the WE electrode potential
within required range. All operational modes of the ROXY Potentiostat are
programmable in the Dialogue (events table). A MS voltammogram can
be visualized in a 3-D or 2-D plots. Information about MS voltammogram
acquisition can be foun
d in the Dialogue for ROXY™ EC system user
guide (p/n 210.7017). Optimization of the working potential and the con-
struction of a hydrodynamic and scanning voltammogram using ROXY Po-
tentiostat keyboard are described in the next section