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Mercury chloride film anode
T.
60
KUWAXA,
R.
S.
k-01,. 20 (r959)
ADAMS
J. Clrrr~. Sm., (1957) 3370. G 1.L. I’. I:,II.~Hs, 1). J. G. IVES AND I<. IV. I’ITTWAN, 0 1,. CllltxsT hsf> I,. lQ~t:~(;IIois, I ~7Icrmlio~iul C’mnmiffee o/ G1cclrochenricul I’hcrwzodyuunlics Kirzetics, 6//t nwclirrg:. 13uttcrwortlis Scientific I’utAic;~tions, London. I 955# p. 273. ’ ‘I’. Jiuv.‘,\s,\ .\sI> I<. 8. hl,,\ats. ./. .,J ))I. C/ic~. .%JC., 79 (1957) 3609. n C. S. RI:ILLICY. C;. \\‘. 1Svw~x.r ASU K. 14. JOIISS, And. Chew., 27 (1955) 483. ” R. 1%. hr>,\sls. J. II. ;\IcC:I,C;HI’, ,\sI> J. XIOHISIS, /J~ul. C/re,rt., 30 (1958) 471. lo I,. <;iI:tKr AND I\. JI:I_IAI. j. ~‘hys. C/rem., 57 (1953) 701. lnterscicncc I’ublisticrs, .Vcw I~rsfrrl~~~a~rlctl.\~lc~fhc~dsin Rlrcfrockc~~,rislry, ‘1 I’. I)liL,\HAY, Sew York. 19.~4. 12 I. 51. l <:. S. MII.LI:I~. ./. .4 ~1. C/rem. .Soc.. 63 (194 I) I 40-5.
1:’ I-. ” I’.
I~I
KIVALO,
I’. I~I:I,,\IIA\Y. ./. /Jr,/. C/rr:,,r. .%c.. ASI> It. A. Lhl’risf~s, I<. 13. OLUIIA~I
,~SIJ
75
J.
(1953)
uud
Inc.,
,)zo_.j.
/Jwr. Chew.
Sot.,
75
Ikwivtrd
(1948)
+I.@.
April
rOth,
ryj8
An investigation of tlw anoclic passivation phcnomcnon at tlw mercury pool clcctroclc in tlw prcscncc of cliloriclc ion 11;~sIccl to tlic dcvdopmcnt of a Ncrcury Cliloricle Film AIIOC~C (hICI;A). Its characteristics as appliccl to the osiclation of substances by the cllronol>otcntionlctric mcthocl wcrc’ rcportctl carlicrl. In clironopotcntiomctry the film wils formctl in the prcscncc of tlic substance to lx lcci to difficulties of oxitlizccl in the lx~clqyouticl potassium chloride! solution. ’ ‘I’liis non-rcl”o(l~icihility or no passivation in cases klwrc tll;! substance to bc ositli;wci forinccl vc2rJ;stable salts with mercurous ion, or was strongly nbsorlwcl on tlic mercury surface. This difficulty may lx climinatccl by forming the film by voltage-scan prior to tllc intrucluction of tlic osidixablc substnncc. ‘I’lw objcctivcs of this pupcr wcrc’ to w;dui~tC: tlw cliaractwistics of tlic MCFA as ,a workitlg anoclc for tllc o_sichtion of substances by tllc \*OltZlgC!-SCiUl mctliotl. As a useful analytical tool, iL mctliocl of rcproclucibly forming tlic film and applying it th osiclations will bc cliscussccl. ‘L’lic variation of peak current with concentration, sensitivity, and half-peal; potentials Ol~ti\iIlCXl will 1x2 comparcxl with tiic previously rcportcd cllronol,otcntioni~try work.
pJ”l
\\'lLS I *Go
.. c1112.
‘I’tic pdnrizing cllancct-‘(hlctron
lo-turn I4ctipot. It was conncctctl unit was :L 50-ohn~ :\_o.s (ffo tiniaritv l~v il rcvcrsiblc. svnclironoiis Instriimcnt (‘0.. I’)cnvcr. Cola.) tl;ivcn
<
to a spxd motor. E3v
VOL.
MERCUR\-
20 (r()yj)
‘1’11~currents bc~x in scrii:s
wcrc dctermincd
with
tbc
circuit
CHLORIDE
I:ILM
ASODE.
by measuring
using
a \‘nrinn
II.
f-31
the vultagc drop ;Lcro~s n calibrntctl recc,rtlcr (10 tnV frill scdc clcflcction).
tlcc~lc
rcSist;inCc
Nodnnil>ing was of the rccorclcr (I scccmtl full
applied and the pen movement was limited cmlv by the maturd pcriotl sc;llc:). ‘I’hc chart speed of the rccortlcr was 1 in./rnin. ‘I’lic clcctrodc potential ucrsris an iiuxiliary satiiratcd c;~luni+l rcforcncc clcctrotlc (S.c’.lS.) was iLISt>monilorctl liy a I.cctls ancl Sortliriip model +GJ pH meter which fctl into ;L l..ccils ant1 Xortliri8l~ USCCI wllcn it W:LS Spcdomax rcccdcr ;icljustcrl for a r.o-\’ fnll scale tlcflcction. This systcnl \\*iLS tlcsirccl to compnrc the applied voltngc to the cq)Cr;itccl at il chart speed (,I 2 in./inin. I~c4dilclwni :\pp:;r;itus ~Yoinprrny instrument Stack solutic>n of o.lobI potassium clrloridc (background clcctrulytc) was prq)nrctl fresh
actual
potential
of
tl~cclcctrotlc.
CilCll
1’11
illlj1lSt~tl
scric5
to
CU.
2.5
(Iiyilrc~clil~~ric
ilCiCl
I.antl
N rtrcortl~*r
nicrcury was used witlicmt furtlrcr purific;iticm. with ~ZI ntljustcd 1,~ l~ytlrc~cl~luriC itcicl 1o illl(tllt 2 .s cvcry 3 (lays for reasons prcviclusly tlcscril~cd~. ‘I’lrc:
~a.01~11stock solutictns of c~xitlizal~lc stll>stnnc~s wcrc pr’clztrccl c(lnt;tining .%lltl
‘I‘llc
or
scldiiiin
tiydrcixi~lc).
o.~or\f l>ut.i~ssi~lt~lcl~loriclc
‘I’hPy
w*ri:
~lrl*pilrclI
lmicw
to
uf runs.
~\liproximatcly 0.5 ml of mercury was tlclivcrcti to ttic Cil\‘it)’ of tllc Lucite ccl1 Iiy n s.o-ml Iurrct. C’arc: ntllst 1~ t;rkCu against stopcock grcasc or cltlwr corlt;tllli~~:tllts curniq in ctrntnct with tllc rncrcury. ‘I‘(# tllc: ccl1 wus ncltlctl 30 ml of the I);uzk~rt~untl clcctrolytc. ‘I’llC Cdl WilS lll;lCctl in llUSitic~l1 ;lncl till! soliitiw tlC;Wr~LtCtl for Cil. 5 min. After allcrwiri# tlic scdution to cluict, 0.00 \: 1)s. S.C:.E. waS ;~pplicil (point (:. I:ig. I) for approximntrtly ‘I2 niin, or iintil tlic ~X~tl:~ltiiLl of tlic iiic’wury c:lcctri~clc 11s.
S.LK..
as
i~wasiiretl
Fig. I. CurrentA. Go0 mV/ruin.
indcpcndcntly.
voltrrgc curves ts. ~00 rnV/min.
Ccmrcqwiitlctl
fair
mercury
chloritlt:
to
the
film
iL1>l>li<*tl
ftJrmntion
l>l~tCl1tiill.
nncl
‘1’181*
l~ack~roctntl
rWlS0Il
for
m-Scan.
applying this vultrrgc is to rcducc any rnc’rcumus chlclri~lt: formecl on the Surface of the mcrcclry through reaction with tlissdved ox);xen =. More reproducible results are obt;linetl in this manna-. The mercurv pond was then pcdarizctl (WC pc)int I’), l:ig. I) at the clcsitcd rate to an npplitd voltage of cn. -+ I .-) \’ vs. S.C‘.E. ‘I’hc mercury Chlc>ridc film is fcJrTTW\ during thiS voltagc: Scan interval. ,\ftcr reaching the applied voltqe of -+ I ._+t’ vs. S.C. E., the motrlr of the: polarizing unit wns reversctl and the applied voltage rdurnctl tl) -+
solution vs.
S.C.E.
interval
was then stirred by nitrogen, allowed to quiet., and rc-9cannecl from +o. IO V to + I .‘I V It iu important that the rrpplietl voltnKc
A.VD DISCUSSION
Fig. I, 13 shows a typical current -voltage (C-V) curve for the anodic polarization of the mercury pool electrode in the supporting electrolyte solution at a scan rate of 400 mV/min. The first large wave of cu. r2opA peak anodic current is for the formation Rsfamncss p. 67
T.
62
ICUWAKA,
I<. S.
ADAMS
VOL.
20 (q5cj)
of mcrcurous chloride. Two other waves follow it whose half-peak potentials correspond closely to the quarter-wave potentials obtained by chronopotcntiomctry for the same chloriclc concentration and pf1. The peak current of the first wave is the point at which tile freshly formed film first begins to limit tllc oxicintion of mercury to mcrcurous chioridc. ‘I’IIc number of coulonlbs rquircd to reach tllis state is reprocluciblc from run to run within s’yi, and calculates to an initinl film thickness of about 20 A. ‘I’hc other waves which follow also contribute! to tllc unique condition of pnssivation for tllc mercury clcctroclc3. The rc-sc;m of the clcctroclc now callcti tlx Mercury Chioriclc Film Anode (hlC1;A) from +o.roV 7x. S.C.E., indicated in Fig. r by point E, to -j-x.4 V ‘us. S.C.E. gives a fairly flat “rcsicluol” current of lx. 5 f/A. A background wave begins to appear at cu. ‘l’llc peak-type waves, rcprcr .4 V 7,s.SC. 13.$vllicii is tlic uscflil limit of this clcctrotic. sciiting filln formation, are no\\f absent on the rc-scan. ‘I’lie potential of the hICl;A z~s. an auxiliary SC. 13. as nic;lsurcti inciclx9~dently follows tlic applicti voltage within j-5 rnv. ‘I’IIc icvcl of the residual current varies bctwccn 5 and IO/CA from run torun cicpcncling on tlic polarization rate, tlic tinio rcquirccl to return theapplicci voltage to -I-0.10 V 71s. SC. I{. Luicl the rc-scan. ‘I’hc cffcct of tllc 000 my/min scan rate on tlic film formation and rc-scan waves may lx swn in Fig. I, A. Most work rclxxtctl in this paper was ~~crfornicd ;lt a sc;m rxtc of 400 mV/min. ‘1’11~conditions of chioricic concentration alld plr f~l\YnxlJlc for film formation, and intcrfcrcnccs from foreign ions and vibrations rqx~rtcci prc\*iously also apply hcrel.
Curve 13 in Fig. 2 is for the oxidation of ;$.H*ro--“;I! solution of N,X-ciir~iethyl-+i’hcllyicncdialtiinc (1) 1’1’) in the background cicctrolytc at a sc;ln rate of 400 mV/mill. The wcil clcfincci peak-type wave (in an anociic ciircction) is similar to those obtained by %‘I~liUI.I ANI) <:OOlCIr, -4 for voltage-scan p01;Lr0gIXplly at a quiet mercury-pool clecof X-aminotroclc for the reduction of inctai ions. Fig. 2, A shows tlic oxidation I,B,(,-na~~hthaicnetr~~tlfonic acid (Koch’s Acid). Aniiinc, hyclrocluinonc, ;mcl +hyclro~sycliphcn_ylaminc gavcsimilar peak-type waves as rcprocidcccl for 600 mV/min scan-rntc in Fig. 3. In this type of poiarogri~phy the lank current is proportional to the concentration.
2. Pcolc-type nnodic C-V cllrvcs for .FiK. oxidation at hICIiA. A. 8.0.1 o-JM Kocl~‘s Acid. 13. 3.8. ~p-*dJ 111’1’.
Refcvenccs
p.
67
Fig. 3. Pcilk-type anodic C-V curves for oxidation at hICI:A. A. 2.7*lo-4M nnilinc. IS. 4,1*ro-~M llydroquinollc. C. G.o*lc+M P-l~ydroxyrliplict~yl~~minc.
Aniljnc, Ilydrocluinonc., ltraction of ;LIxcvi0usl.v rccorclctl t-c&dual curt-cut. ‘I’hc other uses nn cstrnpdatiot~ of tlw IX~S~liiro of the polarogram Ixior to tlic wnvr! of tile clcctroactivc spccics, Sirlcc at tllc hlCFA tllc rc3i~luiLlcurrent fl~lCtlliltiricnlly that iiiorc consistent rcslilts wcrc Ol)tilillWl i I tllc: Vi\lUC’ of lwaak current (ip) \vaS dctcrmincd ils illNsttXtc
If the dircctim of tlic \*oltagc-scan is rcvcrscd after the peak current is attainecl, and scan-m31 in a less positi\rc direction, a peak-tgc cathodic wa\x~ is obscrvcd for the reduction of the oxidized snbstxncc! remaining near the clcctrodc surface. Sucl~ ;L wave is shown for 3,3’-dimcthyllxnzidinc (o-toliclinc) in Fig. 4. Although no systcmatic study was undertaken to correlate thcsc rcvcrse waves, a gcncral olxcrvation is that such waves only appear for compounds which behave in an approximately rcvcrsiblc: .manner at the platinum electrode. For compounds such as aniline and o-phenylene&amine which show irrevcrsiblc behavior at the platinum electrode, no cathodic wave is observed prior to the reduction of the mercury dhloride film. Xkfevencss
9. 67
T.
64 Oxidalio7t
o/ inorganic
KUWASA,
I<. N. ADAMS
VOL.
20 (1959)
con~*otcntis
Oxidation of fcrrocyanidc ion was not possible by chronopotentiomctry because of mcrcurous fcrrocyanidc formation which prevented the mercury chloride film formation. In voltage-scan where the film is formed prior to the introduction of fcrrocyanidc, a double wave was observed. The first wave at CM. -j-o.15 V vs. S.C.E. is bclicvcd to 1~ for the formation of insoluble mc’rcurous fcrrocyanidc”. The scconcl wave has ;L half-peak potential that corresponds to that obtained at the platinum clcctrodc and is probably the oxidation of fcrrocyanide to fcrricyanide. ‘I’hc peak height of the second wave is proportional to the concentration of fcrrocyanidc. No oxidation was ohscrvcd for xo-3i\/ solutions of Co(lI), Fc(I I), ant1 U(IV). Iodide and bromitle ions form more insoluhlc salts with mTIc’rcurousion than chloride and rcmovc the film. Visible crystals of mcrcurotIs iocliclc: or bromide then appear on the surface of tlic mercury pool.
‘I’tic oxiclation of tlic amino group in fi-nitroaniline is difficult at a Pt elcctrodc. ‘l’hc wave occurs at such positive potentials that it is merged with tllc background. Well tlcfinccl oxidation wave’s arc’ obscrvcd at tlic MCi;A at about 1.1 V vs. S.C.12. Wllilc no extensive survey has been made, it is possible tllat oxidations which arc difficult at 1% ant1 AII clcctrodes may bc accomplished at the MCFA. It is evident tllat tllc MCFA, when strippecl of its film can IX opcratccl as IL convcntional mercury pool cathotlc. ‘I’hc intcrcsting possibility exists of carrying out hot11 oxidations and reductions on the same solution. +-Nitroanilinc IUS a reducible nitro group as well as the oxidizable amino function. It was found possible to first oxiclizc the amino group, then, after stripping the mcrcurous cllloritlc film, reduce the nitro group. ‘I’l~c ratio of oxidation to rctluction current observed was approximzltcly I to IO. ’ The nitro reduction uncler thcsc conditions is a h-electron proccss”.
4. Oxidation of 3,3’-dimctl~yll~c~~zitline followcd by rcvcr~c scan. Scmncd anoclicillly from right to left, rcvcrvccl and scannccl in a cathodic direction. Fig.
i
Fig.
5. Peak current
us. square toot of scau 3.r.lo4M,
rate. 13PP concentration
Scrtsitivil) ‘flw sensitivity of the UCFA is about IO fold greater by \*oltagc-scan than chronopotcntiomctry. Further incrcasc of scnsiti\-ity in conventional voltage-scan may be accomplished by increasing the area of the clcctroclc, increasing the scanning rate, or by stirring the solution. The main limitation which dctcrmincs the masimum scnsitivity is still the ratio of the rcsitlual current to the peak osiclation current. A ro-4J1 concentration of l)l’l’ gives approsimatcl~ IL) it.4 current. This is about the lower limit of sensitivity wllcrc* tlic residual current to tlic osidation current approaclics a f : r ratio. In conventional cluict pool polarography4 the peak currents arc proportional to the sciuarc root of tllc SCilll-Klt~‘, I.“‘*. This rclationsllip also applies at the hICl:A. liig. 5 rqxucnts tlic cspcrimc:i~t;dl~ tlctcrniincd uir~c! of ip 21.0.I**“*for ,3.2*1o-J.1f lIPI’ in the hackground clcctrolytc. ‘I’lic~ ~aluc of ip tlccrcascs at higher scan-rates. One passiblc rcxwm for this dccrcasc Imay hc due to the IiWgW i/C drop which appears for the larger currents at higher scan-rates. l’hc actual potential of tlw clcctrodc then lags bcllintl tlW ill~l~liCtl lmtentid. 1Cnl~anccd sensitivity may ;rlso hc: gi1int.dthrough stirring of the solution during the scan. Although sharp \-ihrations tend to rllld,urc: the film, mild stirring hy nitrogen lmhhlin~ through a sintcrcd gliLSSclc:lcrilting tulw cnii 1x2tolcratcd. A prcliniinary cspcrinwnt witlr stirring by nitrogen while osidixing 111’1’ intlicatcs that at least a two fold incrcasc in sensitivity is possible.
‘I’hc rcproclucihility of the peak current from dily to clay \vas checked for a period of a week at two scan-rates of 000 and 2800 mV/tnin. Fresh stock solutions of potassium chloride ant1 IIPl wc’rc prcparcd daily. The concentration of DPl’ was j.z*ro-*J1. Tlic data are shown in Table 11. III several instances, rc-runs \vcrc made on the same IlCFA and solution after stirring the solution hy nitrogen and rc-setting the applied voltage to +o.ro V vs. S.C.l<. The clay to day rcprodllcihility for 9 runs is &y$. The rcproducihility of r-3 rc-runs on the same hICF.4 illld solution is bctwccn 2-q”&.
7’1112 hnlj-ficak
ljotcxtial
'1'11~ potential at the point whcrc the current was one-half the peak value was dcsignatcd as the half-peak potential, ITp. l’hc ITp x*alucs ohtaincd at the MCI:.4 for m;my organic compounds are in good agrccmcnt with EI/, values ohtaincd at the 1% electrode under the same conditions of per. The agrccmcnt of Ep values from run to run is cn. 2 14,. Table 1 gives the reproducibility of 6p values for changing concentrations of Koch’s Acid and IIPP. The values rcportcd arc corrcctcd for ii< drop of the circuit, The 6p values dctcrmincd at the MCFA arc summarized in Table II 1. In the few GSCS whcrc the agrcemcnt with the value obtained at the 13 electrode is poor, the Ep valacs arc always shifted towards more positive potentials. Table I IT contains cln-onopotcntiomctric results at the MCFA and platinum clectrodcs for comparison. Column 5 of Table I gives the total number of coulombs required for the formation of the film to.00 to +r.z V vs. S.C.E. prior to the oxidation of DPP and Koch’s Acid. References
p. 67
i,
al I;00
nr V/uritr
I
in 111 1800
(prlj
ite-runs _._. --.
+nVlmin
(IrAj
He-runs ___-._ _--. ... .I 1
2 I OS.0
112.0
101.3 101.4 102.2
. .. _ _ 1
107.0
107.0
102.8
lO0.b
103.5 102.2
59.0 57.5 Avcmfq2
102.5 =fi 1.3 I .3X
I hzviatiun ______---_---
COMI’,\NISC>N
01’
En/,
ASI>
.-.-------.
611,
-
VALUIIS
- ---
Cowp’~torcf
AT
____.____
I) 1’1’
;! . 7
hnilinc
4.3 2.7 3.5
.(.O
p- I’licnylcnccli;Iniinc 1I > tlroquinonc fi-Nitrcmnilinc p-1 Iyrlroxytlil~llcrlyl;irlliiic o-Tolitlinc ICocli’?c r\citl 1I-Acid 2,5-I)itiicrc;lptc,- i .3.,l-tiii;iili;~zolc I, I o-a-I~licniultl~rolitic fcrrou~ l:crrclcyon itlc ~icrr(Jlls ion Col,alt( I I) IJranirlrn( IV) luclitlc ion __~-.._-_--.. .--.-- ---41 Poorly 1~ Ihta
1: Not
tlcfi iictl of
wave. lJ~\~t~~~ ANI>
Possible
(N.l’.)
at 1’El 9.0. L’ Vtrlue at p1c 1.2.
d
AND
1%
2 .o 3.2 2.7 2.6 2 .o 2 .o 3.’ 1.7 2.6 3.5 2.7
l?LI:.CTHODIS
.__. - ___...^. --..
iowefry
I:‘,/, 1’1 lx,, -..- . .. -_-
____._.-.-_---_-
o-l’licilylciictli~~t~iinc
-..-
CIwr~wpnlo~f _-_-. ..__. ._
PII
_ _._____
MCI’A
0.4 I o.33 0.85 0.8 I
.vC’I**rl
-.-_I’olnmgruphic .__...._. - ..-- .-._.I:‘,/, 1’1 l”fi hfCI*A _._...___.--
--
0.37 0.33 -
-
0.82
-.
0.43” -
0..)1 N.l’.r 0.33 0.51 0.7G -
0.5 0.95 -0.80 -. -
I.10
0.90
N.l’.f N.0.g N.O. N.O. N.P.
0.40
0.43 0.85 -
0.3W 0.4tSJ 0.37” -_ 0.50 OSOd 0.73c 0.20 I .05 -
K? N.O. N.1’.
^--.---
Anhnls7.
: oxidation
\viL\‘c mcq.pt
with I~ackgrountl
WZLVC,
ViLIllL?
f Fcrrocynnitlc LI No Oxidation
I~c/cromzs p. 67
intcrfcrc!, Obscrvctl
with film form~tkm (N.O.).
tlur* tu rcnction
with
mcrcurous
0.70 0.63 0.61 1.1 0.35 0.50 0.78 0.5G cn. 0.66n 0.40
ion.
It may Ix seen that tlrc k’p’s arc indcf~cntlcnt of tlw numhcr of coulombs rccluired fur tlw film. Occasionally, pL-lral~s one orrt of cvcry x0 runs, tlic film formation wa\w wcrc lar~c. Since tlrc E’p vitliics bccomc clcpcndcnt on tlie film tliickncss above a certain tIli~SinlUln, an arbitrary uyqwr limit of ro- ro-8 coulombs wxs set for tlw film formation Wil\‘C. l’liis corrcsponclcd to a maximum peak current for tlw first filnr yaw of 200 yrA using a scan-rate of 400 mV/min. il~ClltS intcrfcrc lllilrly tlic cllrotlopotctltioliictric mctllotl.
‘l’lrc ilUtl\OrS arc ~ratcful to tllc Itctl to l<. ‘1’. IwhSlcrrr) fnr Iris Irc~lpfulsuggestions during tlw course of tlris w-ork, and to YII~\I~II~\1i1rr.1,~ for :ls&t.i\rrc(~ in l)rcfwin~ tlrc manrrscript.
‘1’1~ hlcrcrlry Clrloridc Film ;\l~cxlc (>lC’l;r\) is prq>~>sccl as a wcbrking iI1Iotla which may !~a\-o organic in~Ax11lcs it shcnvs tlcsira1Ac Imqxrtics fc)t oxidati011 c>f organic ni~~l~~ilrs. l;or many clinractcristics coiiiparablc to the pl;xtincini rlcctrcxlc. It 11~s a IriKllcr I~nckp-c~~11rclovclrvc>ltaKc tll;\n the l)lntin~lm clcctrcxlc. 1'11~ l><>l;lrc>gr;~pllic W;IVC A well-tlcfiilrci w.avc is cd>scrvctf nt tlic of ~-11itrc~n1~ili1icis not ol~tniirr~l at I\ platiiiiini clnctrodc. r\l<.:l;;\ at cn. 1,t \’ 7:s. snttrratctl calomcl clrctrcxlc. l’hc sensitivity of the XICITA by voltaKc-scan is soii~c 10 fcdtl grcntcr tIi;rii tlint of clirc~iio~~c~tciitioI’rcli1l~illi~ry cxpcrirncnts indicntc that scnsiti\*ity ma\ lw* cnlr~iicccl 1,s stirrinlr, of tlic rtrctl-v. .
!4c,l11&>11.
1 i!ic ancxlc B filni tic clilorc1rc clc nicrciirc rst pr0posC’c pur I’oxytlaticm cl0 11ic~lc’ci~lcsorfp.iriqucs. cWcn1ic par chrcmo1a scnsilGlit6 par .,\*oItn~c-scan” cnt cnvirctn tlis fois plus grandc qii( * ccllr p~tcntionrdtric. l.>cs cxldricnccr lx-&iniinnircs montrcnt q11c In scnsibilitd 1~~1: i?trc airdliordc par agitation de la solution.
Die ~~1ccksillxrchloritifilnr_nnc,cir I#sst sic11 xnr ancxiisclrcn Oxytlation van organiscllcn S11bstnnist unpzf8lrr 10 nlnl @Wicr als die xon vcrwcndcn. 1Xe Ilmpfintllichkcit tiurclr , ,\‘dtaRc-Scan” lurch lwi chronolx~tcntion~ctrischcn Alcss11ngcn. \‘crsnchc habcn gczcigt, r as%die 1Smpiindlichkcit t liiihrcn dcr l.ib~nK noch gcstcigcrl wnrrlan knnn.
1’. KI;WAXA ASI) 13. N. AI)AMS. .d?rnl. Ckfm. Ada, 20’(1959) 5~. 1. %I. ~~01.Tll0I~F ANI) J, JoRI>As,./. Am. Clrcm. .%c.. 77 (1955) 321 j. l-1. 1’. ~‘)IBHS, 1). J. C;. lvrzs ASI> l<. \V. PITTMAS, J. C‘krm. S-/c., (1957) 3370. C. A. S7mt1x1 hsl> \\‘. 1). C~ooKw. Ajtccl. Chrm., 25 (1953) 1091. 13~~ SAHAI SAXKSA AND c. s. 13HATSAGAR, J. Indian C/rem. sot., 31 (1954) 157. Vol. 11, Chapter 42, lntcracicncc 1. M. KOLTHOIW ANIJ J. J. LINCAWC. PoIaro~vapi~y, Inc.. New York, 1~52. 7 R. E. PARKER AND IL N. ADAMS, Anal. Clretn., 28 (x956) 828.
1 2 8 4 6 a
.Received
I~iil~lishcrs,
April rcjth, zg58
60
KUWAXA,
R.
S.
k-01,. 20 (r959)
ADAMS
J. Clrrr~. Sm., (1957) 3370. G 1.L. I’. I:,II.~Hs, 1). J. G. IVES AND I<. IV. I’ITTWAN, 0 1,. CllltxsT hsf> I,. lQ~t:~(;IIois, I ~7Icrmlio~iul C’mnmiffee o/ G1cclrochenricul I’hcrwzodyuunlics Kirzetics, 6//t nwclirrg:. 13uttcrwortlis Scientific I’utAic;~tions, London. I 955# p. 273. ’ ‘I’. Jiuv.‘,\s,\ .\sI> I<. 8. hl,,\ats. ./. .,J ))I. C/ic~. .%JC., 79 (1957) 3609. n C. S. RI:ILLICY. C;. \\‘. 1Svw~x.r ASU K. 14. JOIISS, And. Chew., 27 (1955) 483. ” R. 1%. hr>,\sls. J. II. ;\IcC:I,C;HI’, ,\sI> J. XIOHISIS, /J~ul. C/re,rt., 30 (1958) 471. lo I,. <;iI:tKr AND I\. JI:I_IAI. j. ~‘hys. C/rem., 57 (1953) 701. lnterscicncc I’ublisticrs, .Vcw I~rsfrrl~~~a~rlctl.\~lc~fhc~dsin Rlrcfrockc~~,rislry, ‘1 I’. I)liL,\HAY, Sew York. 19.~4. 12 I. 51. l
1:’ I-. ” I’.
I~I
KIVALO,
I’. I~I:I,,\IIA\Y. ./. /Jr,/. C/rr:,,r. .%c.. ASI> It. A. Lhl’risf~s, I<. 13. OLUIIA~I
,~SIJ
75
J.
(1953)
uud
Inc.,
,)zo_.j.
/Jwr. Chew.
Sot.,
75
Ikwivtrd
(1948)
+I.@.
April
rOth,
ryj8
An investigation of tlw anoclic passivation phcnomcnon at tlw mercury pool clcctroclc in tlw prcscncc of cliloriclc ion 11;~sIccl to tlic dcvdopmcnt of a Ncrcury Cliloricle Film AIIOC~C (hICI;A). Its characteristics as appliccl to the osiclation of substances by the cllronol>otcntionlctric mcthocl wcrc’ rcportctl carlicrl. In clironopotcntiomctry the film wils formctl in the prcscncc of tlic substance to lx lcci to difficulties of oxitlizccl in the lx~clqyouticl potassium chloride! solution. ’ ‘I’liis non-rcl”o(l~icihility or no passivation in cases klwrc tll;! substance to bc ositli;wci forinccl vc2rJ;stable salts with mercurous ion, or was strongly nbsorlwcl on tlic mercury surface. This difficulty may lx climinatccl by forming the film by voltage-scan prior to tllc intrucluction of tlic osidixablc substnncc. ‘I’lw objcctivcs of this pupcr wcrc’ to w;dui~tC: tlw cliaractwistics of tlic MCFA as ,a workitlg anoclc for tllc o_sichtion of substances by tllc \*OltZlgC!-SCiUl mctliotl. As a useful analytical tool, iL mctliocl of rcproclucibly forming tlic film and applying it th osiclations will bc cliscussccl. ‘L’lic variation of peak current with concentration, sensitivity, and half-peal; potentials Ol~ti\iIlCXl will 1x2 comparcxl with tiic previously rcportcd cllronol,otcntioni~try work.
pJ”l
\\'lLS I *Go
.. c1112.
‘I’tic pdnrizing cllancct-‘(hlctron
lo-turn I4ctipot. It was conncctctl unit was :L 50-ohn~ :\_o.s (ffo tiniaritv l~v il rcvcrsiblc. svnclironoiis Instriimcnt (‘0.. I’)cnvcr. Cola.) tl;ivcn
<
to a spxd motor. E3v
VOL.
MERCUR\-
20 (r()yj)
‘1’11~currents bc~x in scrii:s
wcrc dctermincd
with
tbc
circuit
CHLORIDE
I:ILM
ASODE.
by measuring
using
a \‘nrinn
II.
f-31
the vultagc drop ;Lcro~s n calibrntctl recc,rtlcr (10 tnV frill scdc clcflcction).
tlcc~lc
rcSist;inCc
Nodnnil>ing was of the rccorclcr (I scccmtl full
applied and the pen movement was limited cmlv by the maturd pcriotl sc;llc:). ‘I’hc chart speed of the rccortlcr was 1 in./rnin. ‘I’lic clcctrodc potential ucrsris an iiuxiliary satiiratcd c;~luni+l rcforcncc clcctrotlc (S.c’.lS.) was iLISt>monilorctl liy a I.cctls ancl Sortliriip model +GJ pH meter which fctl into ;L l..ccils ant1 Xortliri8l~ USCCI wllcn it W:LS Spcdomax rcccdcr ;icljustcrl for a r.o-\’ fnll scale tlcflcction. This systcnl \\*iLS tlcsirccl to compnrc the applied voltngc to the cq)Cr;itccl at il chart speed (,I 2 in./inin. I~c4dilclwni :\pp:;r;itus ~Yoinprrny instrument Stack solutic>n of o.lobI potassium clrloridc (background clcctrulytc) was prq)nrctl fresh
actual
potential
of
tl~cclcctrotlc.
CilCll
1’11
illlj1lSt~tl
scric5
to
CU.
2.5
(Iiyilrc~clil~~ric
ilCiCl
I.antl
N rtrcortl~*r
nicrcury was used witlicmt furtlrcr purific;iticm. with ~ZI ntljustcd 1,~ l~ytlrc~cl~luriC itcicl 1o illl(tllt 2 .s cvcry 3 (lays for reasons prcviclusly tlcscril~cd~. ‘I’lrc:
~a.01~11stock solutictns of c~xitlizal~lc stll>stnnc~s wcrc pr’clztrccl c(lnt;tining .%lltl
‘I‘llc
or
scldiiiin
tiydrcixi~lc).
o.~or\f l>ut.i~ssi~lt~lcl~loriclc
‘I’hPy
w*ri:
~lrl*pilrclI
lmicw
to
uf runs.
~\liproximatcly 0.5 ml of mercury was tlclivcrcti to ttic Cil\‘it)’ of tllc Lucite ccl1 Iiy n s.o-ml Iurrct. C’arc: ntllst 1~ t;rkCu against stopcock grcasc or cltlwr corlt;tllli~~:tllts curniq in ctrntnct with tllc rncrcury. ‘I‘(# tllc: ccl1 wus ncltlctl 30 ml of the I);uzk~rt~untl clcctrolytc. ‘I’llC Cdl WilS lll;lCctl in llUSitic~l1 ;lncl till! soliitiw tlC;Wr~LtCtl for Cil. 5 min. After allcrwiri# tlic scdution to cluict, 0.00 \: 1)s. S.C:.E. waS ;~pplicil (point (:. I:ig. I) for approximntrtly ‘I2 niin, or iintil tlic ~X~tl:~ltiiLl of tlic iiic’wury c:lcctri~clc 11s.
S.LK..
as
i~wasiiretl
Fig. I. CurrentA. Go0 mV/ruin.
indcpcndcntly.
voltrrgc curves ts. ~00 rnV/min.
Ccmrcqwiitlctl
fair
mercury
chloritlt:
to
the
film
iL1>l>li<*tl
ftJrmntion
l>l~tCl1tiill.
nncl
‘1’181*
l~ack~roctntl
rWlS0Il
for
m-Scan.
applying this vultrrgc is to rcducc any rnc’rcumus chlclri~lt: formecl on the Surface of the mcrcclry through reaction with tlissdved ox);xen =. More reproducible results are obt;linetl in this manna-. The mercurv pond was then pcdarizctl (WC pc)int I’), l:ig. I) at the clcsitcd rate to an npplitd voltage of cn. -+ I .-) \’ vs. S.C‘.E. ‘I’hc mercury Chlc>ridc film is fcJrTTW\ during thiS voltagc: Scan interval. ,\ftcr reaching the applied voltqe of -+ I ._+t’ vs. S.C. E., the motrlr of the: polarizing unit wns reversctl and the applied voltage rdurnctl tl) -+
solution vs.
S.C.E.
interval
was then stirred by nitrogen, allowed to quiet., and rc-9cannecl from +o. IO V to + I .‘I V It iu important that the rrpplietl voltnKc
A.VD DISCUSSION
Fig. I, 13 shows a typical current -voltage (C-V) curve for the anodic polarization of the mercury pool electrode in the supporting electrolyte solution at a scan rate of 400 mV/min. The first large wave of cu. r2opA peak anodic current is for the formation Rsfamncss p. 67
T.
62
ICUWAKA,
I<. S.
ADAMS
VOL.
20 (q5cj)
of mcrcurous chloride. Two other waves follow it whose half-peak potentials correspond closely to the quarter-wave potentials obtained by chronopotcntiomctry for the same chloriclc concentration and pf1. The peak current of the first wave is the point at which tile freshly formed film first begins to limit tllc oxicintion of mercury to mcrcurous chioridc. ‘I’IIc number of coulonlbs rquircd to reach tllis state is reprocluciblc from run to run within s’yi, and calculates to an initinl film thickness of about 20 A. ‘I’hc other waves which follow also contribute! to tllc unique condition of pnssivation for tllc mercury clcctroclc3. The rc-sc;m of the clcctroclc now callcti tlx Mercury Chioriclc Film Anode (hlC1;A) from +o.roV 7x. S.C.E., indicated in Fig. r by point E, to -j-x.4 V ‘us. S.C.E. gives a fairly flat “rcsicluol” current of lx. 5 f/A. A background wave begins to appear at cu. ‘l’llc peak-type waves, rcprcr .4 V 7,s.SC. 13.$vllicii is tlic uscflil limit of this clcctrotic. sciiting filln formation, are no\\f absent on the rc-scan. ‘I’lie potential of the hICl;A z~s. an auxiliary SC. 13. as nic;lsurcti inciclx9~dently follows tlic applicti voltage within j-5 rnv. ‘I’IIc icvcl of the residual current varies bctwccn 5 and IO/CA from run torun cicpcncling on tlic polarization rate, tlic tinio rcquirccl to return theapplicci voltage to -I-0.10 V 71s. SC. I{. Luicl the rc-scan. ‘I’hc cffcct of tllc 000 my/min scan rate on tlic film formation and rc-scan waves may lx swn in Fig. I, A. Most work rclxxtctl in this paper was ~~crfornicd ;lt a sc;m rxtc of 400 mV/min. ‘1’11~conditions of chioricic concentration alld plr f~l\YnxlJlc for film formation, and intcrfcrcnccs from foreign ions and vibrations rqx~rtcci prc\*iously also apply hcrel.
Curve 13 in Fig. 2 is for the oxidation of ;$.H*ro--“;I! solution of N,X-ciir~iethyl-+i’hcllyicncdialtiinc (1) 1’1’) in the background cicctrolytc at a sc;ln rate of 400 mV/mill. The wcil clcfincci peak-type wave (in an anociic ciircction) is similar to those obtained by %‘I~liUI.I ANI) <:OOlCIr, -4 for voltage-scan p01;Lr0gIXplly at a quiet mercury-pool clecof X-aminotroclc for the reduction of inctai ions. Fig. 2, A shows tlic oxidation I,B,(,-na~~hthaicnetr~~tlfonic acid (Koch’s Acid). Aniiinc, hyclrocluinonc, ;mcl +hyclro~sycliphcn_ylaminc gavcsimilar peak-type waves as rcprocidcccl for 600 mV/min scan-rntc in Fig. 3. In this type of poiarogri~phy the lank current is proportional to the concentration.
2. Pcolc-type nnodic C-V cllrvcs for .FiK. oxidation at hICIiA. A. 8.0.1 o-JM Kocl~‘s Acid. 13. 3.8. ~p-*dJ 111’1’.
Refcvenccs
p.
67
Fig. 3. Pcilk-type anodic C-V curves for oxidation at hICI:A. A. 2.7*lo-4M nnilinc. IS. 4,1*ro-~M llydroquinollc. C. G.o*lc+M P-l~ydroxyrliplict~yl~~minc.
Aniljnc, Ilydrocluinonc., l
If the dircctim of tlic \*oltagc-scan is rcvcrscd after the peak current is attainecl, and scan-m31 in a less positi\rc direction, a peak-tgc cathodic wa\x~ is obscrvcd for the reduction of the oxidized snbstxncc! remaining near the clcctrodc surface. Sucl~ ;L wave is shown for 3,3’-dimcthyllxnzidinc (o-toliclinc) in Fig. 4. Although no systcmatic study was undertaken to correlate thcsc rcvcrse waves, a gcncral olxcrvation is that such waves only appear for compounds which behave in an approximately rcvcrsiblc: .manner at the platinum electrode. For compounds such as aniline and o-phenylene&amine which show irrevcrsiblc behavior at the platinum electrode, no cathodic wave is observed prior to the reduction of the mercury dhloride film. Xkfevencss
9. 67
T.
64 Oxidalio7t
o/ inorganic
KUWASA,
I<. N. ADAMS
VOL.
20 (1959)
con~*otcntis
Oxidation of fcrrocyanidc ion was not possible by chronopotentiomctry because of mcrcurous fcrrocyanidc formation which prevented the mercury chloride film formation. In voltage-scan where the film is formed prior to the introduction of fcrrocyanidc, a double wave was observed. The first wave at CM. -j-o.15 V vs. S.C.E. is bclicvcd to 1~ for the formation of insoluble mc’rcurous fcrrocyanidc”. The scconcl wave has ;L half-peak potential that corresponds to that obtained at the platinum clcctrodc and is probably the oxidation of fcrrocyanide to fcrricyanide. ‘I’hc peak height of the second wave is proportional to the concentration of fcrrocyanidc. No oxidation was ohscrvcd for xo-3i\/ solutions of Co(lI), Fc(I I), ant1 U(IV). Iodide and bromitle ions form more insoluhlc salts with mTIc’rcurousion than chloride and rcmovc the film. Visible crystals of mcrcurotIs iocliclc: or bromide then appear on the surface of tlic mercury pool.
‘I’tic oxiclation of tlic amino group in fi-nitroaniline is difficult at a Pt elcctrodc. ‘l’hc wave occurs at such positive potentials that it is merged with tllc background. Well tlcfinccl oxidation wave’s arc’ obscrvcd at tlic MCi;A at about 1.1 V vs. S.C.12. Wllilc no extensive survey has been made, it is possible tllat oxidations which arc difficult at 1% ant1 AII clcctrodes may bc accomplished at the MCFA. It is evident tllat tllc MCFA, when strippecl of its film can IX opcratccl as IL convcntional mercury pool cathotlc. ‘I’hc intcrcsting possibility exists of carrying out hot11 oxidations and reductions on the same solution. +-Nitroanilinc IUS a reducible nitro group as well as the oxidizable amino function. It was found possible to first oxiclizc the amino group, then, after stripping the mcrcurous cllloritlc film, reduce the nitro group. ‘I’l~c ratio of oxidation to rctluction current observed was approximzltcly I to IO. ’ The nitro reduction uncler thcsc conditions is a h-electron proccss”.
4. Oxidation of 3,3’-dimctl~yll~c~~zitline followcd by rcvcr~c scan. Scmncd anoclicillly from right to left, rcvcrvccl and scannccl in a cathodic direction. Fig.
i
Fig.
5. Peak current
us. square toot of scau 3.r.lo4M,
rate. 13PP concentration
Scrtsitivil) ‘flw sensitivity of the UCFA is about IO fold greater by \*oltagc-scan than chronopotcntiomctry. Further incrcasc of scnsiti\-ity in conventional voltage-scan may be accomplished by increasing the area of the clcctroclc, increasing the scanning rate, or by stirring the solution. The main limitation which dctcrmincs the masimum scnsitivity is still the ratio of the rcsitlual current to the peak osiclation current. A ro-4J1 concentration of l)l’l’ gives approsimatcl~ IL) it.4 current. This is about the lower limit of sensitivity wllcrc* tlic residual current to tlic osidation current approaclics a f : r ratio. In conventional cluict pool polarography4 the peak currents arc proportional to the sciuarc root of tllc SCilll-Klt~‘, I.“‘*. This rclationsllip also applies at the hICl:A. liig. 5 rqxucnts tlic cspcrimc:i~t;dl~ tlctcrniincd uir~c! of ip 21.0.I**“*for ,3.2*1o-J.1f lIPI’ in the hackground clcctrolytc. ‘I’lic~ ~aluc of ip tlccrcascs at higher scan-rates. One passiblc rcxwm for this dccrcasc Imay hc due to the IiWgW i/C drop which appears for the larger currents at higher scan-rates. l’hc actual potential of tlw clcctrodc then lags bcllintl tlW ill~l~liCtl lmtentid. 1Cnl~anccd sensitivity may ;rlso hc: gi1int.dthrough stirring of the solution during the scan. Although sharp \-ihrations tend to rllld,urc: the film, mild stirring hy nitrogen lmhhlin~ through a sintcrcd gliLSSclc:lcrilting tulw cnii 1x2tolcratcd. A prcliniinary cspcrinwnt witlr stirring by nitrogen while osidixing 111’1’ intlicatcs that at least a two fold incrcasc in sensitivity is possible.
‘I’hc rcproclucihility of the peak current from dily to clay \vas checked for a period of a week at two scan-rates of 000 and 2800 mV/tnin. Fresh stock solutions of potassium chloride ant1 IIPl wc’rc prcparcd daily. The concentration of DPl’ was j.z*ro-*J1. Tlic data are shown in Table 11. III several instances, rc-runs \vcrc made on the same IlCFA and solution after stirring the solution hy nitrogen and rc-setting the applied voltage to +o.ro V vs. S.C.l<. The clay to day rcprodllcihility for 9 runs is &y$. The rcproducihility of r-3 rc-runs on the same hICF.4 illld solution is bctwccn 2-q”&.
7’1112 hnlj-ficak
ljotcxtial
'1'11~ potential at the point whcrc the current was one-half the peak value was dcsignatcd as the half-peak potential, ITp. l’hc ITp x*alucs ohtaincd at the MCI:.4 for m;my organic compounds are in good agrccmcnt with EI/, values ohtaincd at the 1% electrode under the same conditions of per. The agrccmcnt of Ep values from run to run is cn. 2 14,. Table 1 gives the reproducibility of 6p values for changing concentrations of Koch’s Acid and IIPP. The values rcportcd arc corrcctcd for ii< drop of the circuit, The 6p values dctcrmincd at the MCFA arc summarized in Table II 1. In the few GSCS whcrc the agrcemcnt with the value obtained at the 13 electrode is poor, the Ep valacs arc always shifted towards more positive potentials. Table I IT contains cln-onopotcntiomctric results at the MCFA and platinum clectrodcs for comparison. Column 5 of Table I gives the total number of coulombs required for the formation of the film to.00 to +r.z V vs. S.C.E. prior to the oxidation of DPP and Koch’s Acid. References
p. 67
i,
al I;00
nr V/uritr
I
in 111 1800
(prlj
ite-runs _._. --.
+nVlmin
(IrAj
He-runs ___-._ _--. ... .I 1
2 I OS.0
112.0
101.3 101.4 102.2
. .. _ _ 1
107.0
107.0
102.8
lO0.b
103.5 102.2
59.0 57.5 Avcmfq2
102.5 =fi 1.3 I .3X
I hzviatiun ______---_---
COMI’,\NISC>N
01’
En/,
ASI>
.-.-------.
611,
-
VALUIIS
- ---
Cowp’~torcf
AT
____.____
I) 1’1’
;! . 7
hnilinc
4.3 2.7 3.5
.(.O
p- I’licnylcnccli;Iniinc 1I > tlroquinonc fi-Nitrcmnilinc p-1 Iyrlroxytlil~llcrlyl;irlliiic o-Tolitlinc ICocli’?c r\citl 1I-Acid 2,5-I)itiicrc;lptc,- i .3.,l-tiii;iili;~zolc I, I o-a-I~licniultl~rolitic fcrrou~ l:crrclcyon itlc ~icrr(Jlls ion Col,alt( I I) IJranirlrn( IV) luclitlc ion __~-.._-_--.. .--.-- ---41 Poorly 1~ Ihta
1: Not
tlcfi iictl of
wave. lJ~\~t~~~ ANI>
Possible
(N.l’.)
at 1’El 9.0. L’ Vtrlue at p1c 1.2.
d
AND
1%
2 .o 3.2 2.7 2.6 2 .o 2 .o 3.’ 1.7 2.6 3.5 2.7
l?LI:.CTHODIS
.__. - ___...^. --..
iowefry
I:‘,/, 1’1 lx,, -..- . .. -_-
____._.-.-_---_-
o-l’licilylciictli~~t~iinc
-..-
CIwr~wpnlo~f _-_-. ..__. ._
PII
_ _._____
MCI’A
0.4 I o.33 0.85 0.8 I
.vC’I**rl
-.-_I’olnmgruphic .__...._. - ..-- .-._.I:‘,/, 1’1 l”fi hfCI*A _._...___.--
--
0.37 0.33 -
-
0.82
-.
0.43” -
0..)1 N.l’.r 0.33 0.51 0.7G -
0.5 0.95 -0.80 -. -
I.10
0.90
N.l’.f N.0.g N.O. N.O. N.P.
0.40
0.43 0.85 -
0.3W 0.4tSJ 0.37” -_ 0.50 OSOd 0.73c 0.20 I .05 -
K? N.O. N.1’.
^--.---
Anhnls7.
: oxidation
\viL\‘c mcq.pt
with I~ackgrountl
WZLVC,
ViLIllL?
f Fcrrocynnitlc LI No Oxidation
I~c/cromzs p. 67
intcrfcrc!, Obscrvctl
with film form~tkm (N.O.).
tlur* tu rcnction
with
mcrcurous
0.70 0.63 0.61 1.1 0.35 0.50 0.78 0.5G cn. 0.66n 0.40
ion.
It may Ix seen that tlrc k’p’s arc indcf~cntlcnt of tlw numhcr of coulombs rccluired fur tlw film. Occasionally, pL-lral~s one orrt of cvcry x0 runs, tlic film formation wa\w wcrc lar~c. Since tlrc E’p vitliics bccomc clcpcndcnt on tlie film tliickncss above a certain tIli~SinlUln, an arbitrary uyqwr limit of ro- ro-8 coulombs wxs set for tlw film formation Wil\‘C. l’liis corrcsponclcd to a maximum peak current for tlw first filnr yaw of 200 yrA using a scan-rate of 400 mV/min. il~ClltS intcrfcrc lllilrl
‘l’lrc ilUtl\OrS arc ~ratcful to tllc I
‘1’1~ hlcrcrlry Clrloridc Film ;\l~cxlc (>lC’l;r\) is prq>~>sccl as a wcbrking iI1Iotla which may !~a\-o organic in~Ax11lcs it shcnvs tlcsira1Ac Imqxrtics fc)t oxidati011 c>f organic ni~~l~~ilrs. l;or many clinractcristics coiiiparablc to the pl;xtincini rlcctrcxlc. It 11~s a IriKllcr I~nckp-c~~11rclovclrvc>ltaKc tll;\n the l)lntin~lm clcctrcxlc. 1'11~ l><>l;lrc>gr;~pllic W;IVC A well-tlcfiilrci w.avc is cd>scrvctf nt tlic of ~-11itrc~n1~ili1icis not ol~tniirr~l at I\ platiiiiini clnctrodc. r\l<.:l;;\ at cn. 1,t \’ 7:s. snttrratctl calomcl clrctrcxlc. l’hc sensitivity of the XICITA by voltaKc-scan is soii~c 10 fcdtl grcntcr tIi;rii tlint of clirc~iio~~c~tciitioI’rcli1l~illi~ry cxpcrirncnts indicntc that scnsiti\*ity ma\ lw* cnlr~iicccl 1,s stirrinlr, of tlic rtrctl-v. .
!4c,l11&>11.
1 i!ic ancxlc B filni tic clilorc1rc clc nicrciirc rst pr0posC’c pur I’oxytlaticm cl0 11ic~lc’ci~lcsorfp.iriqucs. cWcn1ic par chrcmo1a scnsilGlit6 par .,\*oItn~c-scan” cnt cnvirctn tlis fois plus grandc qii( * ccllr p~tcntionrdtric. l.>cs cxldricnccr lx-&iniinnircs montrcnt q11c In scnsibilitd 1~~1: i?trc airdliordc par agitation de la solution.
Die ~~1ccksillxrchloritifilnr_nnc,cir I#sst sic11 xnr ancxiisclrcn Oxytlation van organiscllcn S11bstnnist unpzf8lrr 10 nlnl @Wicr als die xon vcrwcndcn. 1Xe Ilmpfintllichkcit tiurclr , ,\‘dtaRc-Scan” lurch lwi chronolx~tcntion~ctrischcn Alcss11ngcn. \‘crsnchc habcn gczcigt, r as%die 1Smpiindlichkcit t liiihrcn dcr l.ib~nK noch gcstcigcrl wnrrlan knnn.
1’. KI;WAXA ASI) 13. N. AI)AMS. .d?rnl. Ckfm. Ada, 20’(1959) 5~. 1. %I. ~~01.Tll0I~F ANI) J, JoRI>As,./. Am. Clrcm. .%c.. 77 (1955) 321 j. l-1. 1’. ~‘)IBHS, 1). J. C;. lvrzs ASI> l<. \V. PITTMAS, J. C‘krm. S-/c., (1957) 3370. C. A. S7mt1x1 hsl> \\‘. 1). C~ooKw. Ajtccl. Chrm., 25 (1953) 1091. 13~~ SAHAI SAXKSA AND c. s. 13HATSAGAR, J. Indian C/rem. sot., 31 (1954) 157. Vol. 11, Chapter 42, lntcracicncc 1. M. KOLTHOIW ANIJ J. J. LINCAWC. PoIaro~vapi~y, Inc.. New York, 1~52. 7 R. E. PARKER AND IL N. ADAMS, Anal. Clretn., 28 (x956) 828.
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