Page 119 - Analytical Electrochemistry 2d Ed - Jospeh Wang

104 PRACTICAL CONSIDERATIONS

metric methods that are less prone to oxygen interference. The background
connection capability of modem (computerized) instruments is also effective for
work in the presence of dissolved oxygen.

4-4 INSTRUMENTATION

Rapid advances in microelectronics, and in particular the introduction of operational
ampli®ers, have led to major changes in electroanalytical instrumentation. Tiny and
inexpensive integrated circuits can now perform many functions that previously
required very large instruments. Such trends have been reviewed recently (5).
Various voltammetric analyzers are now available commercially from different
sources (Table 4-1) at relatively modest prices (ranging from $5,000 to $25,000 in
1999). Such instruments consist of two circuits: a polarizing circuit that applies the
potential to the cell, and a measuring circuit that monitors the cell current. The
characteristic of modern voltammetric analyzers is the potentiostatic control of the
working electrode, which minimizes errors from cell resistance (i.e., poorly de®ned
voltammograms with lower current response and shifted and broadened peaks).
Equation 4-3 explains the cause for this ohmic distortion:

E ˆ E E iR 4-3†
app w:e: r:e:
where iR is the ohmic potential drop.

TABLE 4-1 Suppliers of Voltammetric Analyzers

Supplier Address
Analytical Instrument Systems P.O. Box 458, Flemington, NJ 08822, U.S.A.
www.aishome.com
Bioanalytical Systems 2701 Kent Ave., W. Lafayette, IN 47906, U.S.A.
www.bioanalytical.com
Cypress P.O. Box 3931, Lawrence, KS 66044, U.S.A.
www.cypresshome.com
CH Instruments 3700 Tennison Hill Dr., Austin, TX 78733, U.S.A.
chinstr@worldnet.att.net
ECO Chemie P.O. Box 85163, 3508 AD Utrecht, The Netherlands
autolab@ecochemie.nl
www.brinkmann.com
EG&G PAR 801 S. Illinois Ave, Oak Ridge, TN, 37830, U.S.A.
www.egg.inc.com=par
ESA 45 Wiggins Ave., Bedford, MA 01730, U.S.A.
Metrohm CH-9109 Herisau, Switzerland
www.brinkmann.com
Radiometer=Tacussel 27 rue d'Alscace, F-69627 Villeurbanne, France
Analytical@clevelandOH.com
Solartron 964 Marcon Blvd., Allentown, PA 18103, USA
www.solartron.com