Stanford 1. Tackett1 and John A. Knowles Arizona State University Tempe
Simple Pontentiostat for Controlled Potential Electrolysis
controlled potential electrolysis is a wrsatile technique and has bee11 applied to a variety of cheniiaal st,udies. It is used for selective separstinn of metals at solid or mrwury pool electrodes, and for t,heir deternrinat,ion ( 1 ) . The technique is extrcnlely nscfnl in the study of clieniiral kinetics (2). Controlled potential electrolysis can often be made to proceed at 100% current efFieienry for a particular elertrode react,ion, thus furnishing a basis for roulometri(. :malysis. It can also be used to good advantage for selective oxidation or redoct,ion in both orgmic and illorganic preparations. Controlled potential electrolysis requires :I nmdi longer time for rompletion than do elertrolytio n~ethods where 100% current efficiency for the electrode proress of interest is not essential, and precise ninnnill control rrquires eonstmt operator attention. A device for autoniatic potential control would niake rontrolled potential electrolytic methods more prsrtiral and attrartive. Until now, unfortunately, :I successful potentiostat has been a rather complex instru~ntnit,i~nd the rost has been prohibitive for a school or s~nwllIahoratory operating on a limited budget. The automatic potentiostat desrrihcd here is inexpensive, simple in design, and easily ronst,ructcd from readily available materials. Operation of the instrument is extren~elysimple, requiring only the initial setting of the desired electrode potential. The tot,al rest of the parts listed in Table 1 is $135, which may br reduced considerably as outlined below, Low cost and high versatility offer att,ractive possibilities for rourses ill instrument.al andysis, as x w l l as for ronline laborntory applicat,ions. Several surrcssful carlier potentiostats wl~ich usr vacuum tube circuits are discussed by Lingane (1). Modern transistors and diodes are more suit,able for potential c:ont,rol circuits becausc they wc capable of handling large currents at low voltages and are mon: reliable t,han vacuum tubes when used within thrir rdtings. A transistorized circuit. can be simpler in design and less expensivr than a comparable varuuni t,ubo model. Tn.0 recent t,rsnsistorized potentiostals dcsi.ribcd by \Vads\vort.h (3) and Lindstroni and Davis (4) work well for such applications as the elet:trogravinict,rie dcl.crnliriation of inetals. Berausc of the fairly high eerc vin-rents of the i~lstruments,they do not work well for niicrocoulon~etry !diere small iwrrent,s are necessary. The pulsed power supply in thr rircuit of 1,indstroni :ind I h v s nl:llies it rspct:ially iuisuit~cdfor ~ni~.roelei.-
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Present address: Indiana Univemitp nf Iwlians, Pennsylvania
Pwmsylvz~ti:~,
Table I .
, C
' ('3
f'lic-4
I
1'al.b~List
500 mf 111 v IX,001l rnf 10 v 1)iodea included in bridge assembly I h d e s included i n bridec
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I I 5.6 v Zener diode, IN552 5.0 v Zener diode, IN751 CRn
.IT, I
04
,
us
Q
(3 &, QQ 13,
)/,a Sb-Blow, SAC: 11-50 prr de meter &50 pa. dc meter Transistor, 2N3392
Transistor, ZN'2lOR Transiatnr, 2N14R7 F.E.T., 2N2498 Ilesistor, 1811K, 'IrW 10';
84 TI
Switch, SPI)T, toggle 'rrsnrformer, 12.6 v C.T., 1.5 smo. Triad F-25X
I,
amp, Triad F-13X Pilot lamp, neon, Eldenm mG1-CCB-XE"E
trolysis. Thv pot~utiostat reported her(. has I M I W ~ ! ~ supply stabilization a i d sufficiently low zero current t o pern~itaccurate pot,ent,ial contml :~ndcodonrrtric3analysis of mirros:uuplrs. The Instrument
Thr rirvuit (wisists of two s r ~ : t i o ~ ~h s :powrr supply with voltage regulation, and a high input iuipedancr voltmeter for nlonit,oring the actual potential differenw between the working electrode and the ssturat,rd ~ d o m e lreference electrode. The pol\-er supply is :I
