This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: SQUARE—WAVE VOLTAMMETRY In reviewing the techniques of tast polarography, normal pulse polarography. and
differential pulse polarography, one realizes that each technique utilizes a series 9f
individual mercury drops issuing from a capillary at precisely timed intervals. Another form of polamgraphy is called square—wave voltammetry, and one is
immediately struck by the fact that the entire set of measurements is done so rapidly that it can be done with a single mercury drop. Key relerences pertaining to square—wave
voltammetry are as follows: (1) L. Ramalay and M. S. Krause, Jr._, Anal. Chen-1., 41. 1362 (1.969). (2) L. Ramaiay and M. S. Krause= Jr., Anal. Chem, 41, 1365 (1969). (3) J. H. Christie, J. A. Turner, and R. A. Ostetyoung. Anal. Chem, 49, 1899
(197?). (4) .l. A. Turner. .1. H. Christie, M. VLIkOViC, and R. A. Osteryoung- Anal. Chem.
49, 1904 (1977). (5) R. Samuelsson, J. J. O’Dea, and J. Oste1young,Amn’. Chem, 52, 2215 (1980}. (6) J. J. O’Dea, J. Osteryoung, and R. A. Osteryoung, Anal. Chem. 53, 695
(1981). (7) .l. Osteryoung and .1. J. O‘Dea, in li‘fecrroamdyrfcal Chemistry, A. J. Bard, ed.=
Volume 14, Marcel Dekker, lne., New York, 1980. Shown in the ﬁgure below is the excitation wavefomi for modern square—waye
voltammetry; the baseline potential increases by Air.” for each full cycle of the square wave
whose half-height is Es“. and whose period is r, and the current is measured at the end of
each half cycle (times I and 2 in the figure). This waveform is applied to a single drop
from a polarographic capillary; the time interval TL. is designed to allow the drop to grow to a predetermined size (usually to almost its full size just before it detaches from the tip
of the capillary). ' POTENTIAL TIME Figure l. Excitation signal for square-wave voltammetry. [Adapted [rom Reference 7.] Typical results are shown in the ﬁgure below; the current component labeled A is the
current for the forward half cycle (time 1), component B is due to the reverse half cycle
(time 2'), and component C is the difference (curve A - curve B). In appearance, curve C.
resembles that seen in differential pulse polarography; the detection limit for square—wave
voltammetry is between 10"0 and 10"9 M. |5
zoo o -200 ~4oo
nlE—EW) mV Figure 2. Calculated square-wave voltammograms for reversible electron transfer: (A) forward current; (B) reverse current; (C) net current, dimensionless units. [Adapted from
Reference 9.] Reference 7 above provides a comprehensive review of this technique, along with
predictions for the response formally types of complicated reaction schemes. October. 2010 ...
View Full Document
- Fall '10