Edited by GALEN W. WING, Seton Holl University, So. Orange, N. J. 07079
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hese articles are intended ~o serve the readera of m ~ JsO ~ R N A L by calling allation to new developmmls in the them, desiqn, or ( ~ ~ ( ~ i l a b of ility chemical laboraloru instrumentation. or bu m e m l i n a yseful i&h& and ezplanations o j topics thd are of prociieal i & w b n c e I;, thok who G e , or fewh the use of, modem instrumentation and instrumental lechnipues. The edilm invites correspondence from prospective contributma.
1. Pulse Polarography David E. Burge, P. 0.Box 313, Cupertino, Calif. 95014 Polarography is a well estshlished method of chemical analysis and research. Although it has been known for about forty years, it is still in a. state of active development. This discussion will cover one ares, in which real progress has been made in the last ten years; the use of pulse techniques to improve the analytical usefulness of polsrography. As anyone familiar with polsrography is well aware, the usud technique involves using the dropping mercury electrode (DME), applying a. continuous snd linearly changing voltage to the electrode, and measuring the eurrent passing through the cell. The other electrode of the cell is a standard reference electrode such as edomel or silver-silver chloride. If the reference electrode is constructed properly, its potential re1at.i.t.e to the solution will not change with current. Therefore, the t,otal potential applied to the cell will consist, of t,he constant ~ o t e n t i a lof the rrfrrrnw r l w t n # c l ~.I, potential lwtwrrn the .,ulution nnd the working r l r r t r r d thut is thc 1)\11.:-.utd x putentin1 tl~ru~tph the solution due to its resistance. Under these conditions the mercury electrode is completely polarized and, hence, determines the total current flowing through the cell. The current flowing will depend on reductions taking place a t the electrode a t a particular potential, as well as on t,he capacitive charging current required to charge the double layer around each new merculy drop. These two currents me the only ones of significance passing through the cell. Furthermore, since the Faradaic reduction current is the one
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Figure 1. Voltage and current relations in conventional polomgrophy: lo1 Sweep voltage as o function of time; lbl Current or a function of voltage, the "polorogram."
order to increase the sensitivity or improve the measurement limit of the Fsradaic current. Suppression of the effects of charging current is the major reason for the use of pulse techniques. Pulse polsrography was first developed by Barker (I) as an outgrowth of his work with square wave methods. His published work has been summarized by Schmidt and von Stackelberg (2).
Pulse Polarogmphy L e t 18- cw.&lw iu m w c dt.loil the ttsr uf p u l i ~m
