The amperometric and constant current potentiometric titration of ethylenediaminetetraacetic acid with copper (II)

VOL. 20 (1959)

THE

ASALYTICA

AMPEROMETRIC

TITRATION

OF

AND

CHIMICA

CONSTANT

\VII~I,LA\M S. ICNLGHT Rerrsselaer Polytcclrrric

AND

CURRENT

481

POTENTIOMETRIC

ETHYT~ENEDIAMINETETIIAACETIC COPPER

PI
ACTA

MATYsKAI,

AND

WITH

(II) ROl3ERT

Institute,

ACKEIMIANN

ACID

AND

A. OSTBRYOUNG

Troy,

N.Y.

(l7.S.A ,)

SCIIW~~RZENR,\CII”,

AND

I
rcportcd the ampcromctric titration of cthylencdinminctraacctic acid (EDTA) with coppcr(1 I) at the dropping mercury clcctrodc. ‘I’ANAIW, KO~AMA, SASKI, As1) SUCINO~ titrated copper with ED’l’A in an acetate buffer of p114.2 using the dropping mercury clcctroclc. indicator clcctrodc for the 151Y1’A NIICISLLISY ASI) COOKE” usctl the mercury-pool cases, titrations were titration of micromolar solutions of copper. In favorable successfully cilrricd out at concentrations approaching ro-Till. l’I~~14 have reported the cletcrmination of copper by adding cscess ED’TA and backtitrating with lead ions using the platinum-tungstan system. Copper was titrated automatically by HASLAM, SQUIHHEI.L, ANJ) f-~ESICISS1” using disodium dihydrogen eth_vlencdiaminetctraacetatc. The end-point was taken
hsn

References

Q. 485

‘I’mfm1c~

482

W.

S.

KSIGIIT,

R.

A.

OSTBI
VOL.

20 (1959)

potentiomctric titration of ~IC;IITIS~Al.l~, both using tlic rotated platinum electrodc as indicator elcctroclc, wcrc tried in an acidic solution, ratllcr tllan in basic solutions ~~scttl by tlrc: majority of the alx~c rcscarcllcrs.

cc~l~pcr( I I) sc~ltttic~rts wr2rc’ prcpuwl from tilt2 Mclins Co., C.~lc~‘tZli~tltl, Ohio, diltttion to volume. Stwttlwxl eolutions of ISIYI’A wcrc Itrcparcrl ~IIXI~CII cthylctlctli;rtt~itIctctr;~;rcct;rtc tliltytltxtc I’ltillilwl,ttrg, N. J., in Wirtcr :ttltl stirnclilrrlizing indicator. All cItctiiic:rls wcrc: rcngctit grwlc. St~llltlill~tl

Ol,t.i~iIlCd

I,y solutiott in it minimtttn

of No. ;rmotttit

18 clcxtrc~lytic of nitric

acid.

copper wire followed by

by dissolving “Uakcr Annlyzed” tliuodittm c~lAa.iticd from the J. ‘f. Uirkcr Chcmicxl iLf+itlSt standartl copper t1sit-q Mttrcxitlc

clihyCo.. as ill1

‘I’lio Szrrfq2nl SIC~tltli~l I’c~hrogral~h. ;\Iotlcl I II, matlc lly Ii. IL. Sargent and Co., Clticago, Ill., aricl il llt;lnlli~l polirrct~rrplt constrtrctctl in tltc Rcttsschcr I’olyl.cclinic Institittc Cltcmistry IX+ ~~iLrttllCIlt wurc ~tsiccl.‘Tltc rutatctl phtittutn wit-c tnicro clcctrotlc was ITtiKlc of No. t 8 pkrtinum wire with 0.5 ctii cxl>oscCI to solution. It was clrivcn at Go0 r.p.m. by :L Sargent Synchronous Alotor. ‘I’ypc JCY(Az. I’cttcntial?c Wcrc rnc;wurotl wit11 a ‘I’riplctt Jlodcl GZO V’I’VRI. Serial No. GGr)r . The cut-tent for tltc! constnttl current l~otctttic~tlictric titriltions was nttpplictl through il large scrics rcsietor by R I h-V Ixittcry.

Polurograms of the copper-ElYL’A titration were run in a o.z.11 acetate buffer of pt1 5.0 at tliffcrcnt points in the titration using tlw rotated platinum micro dcctroclc (Ii. ll.15.) 71ersI1.s the snturatccl calomcl clcctrotlc (S.C.E.) with tlic manual l~olilrograp\I hilt at Rcnssclacr Polytcclinic Institute. Typical ~darograms arc shown in Fig. I, wlwrc A is so’;:, to cncl-point, 13is I’%, bcforc cnc.l-point, mu.1 (Z is f ‘%, after cntl-point I 240 -

I

I

I

---7

1

200-

a _1100f

5

,m.--

U 00, 5,-

oo-

Fig.

r.

hhrogt-ams

of Clt-ED’l’h

titrirt;iotl.

Fig.

2.

Ampcromctric

titrationof

EDTA.

in the titration of ED’I’A with Cu(l1). ‘I’hc solutions wcrc ClC!@iSSC!Cl with a glass-frit l~ubblcr for rg min with nitrogen before each polarogram and continously during tllc polarogram. For all espcrimcnts, the platinum clcctroclc was cleaned by washing with cont. nitric acid ancl then placed in tlistillccl water and shorted to the S.C.E. until no current flowed through the circllit formed. ‘I’hc amperomctric titration of EL)‘I’A with coppcr(II) was pcrformccl in a roo-ml 1XXkW containing 50 ml of buffer ant1 ro ml of ED’I’A solution using the R.P.E. at an appliccl potential of about -0.45 V 71s. S.C.E. Rr/ercrrces p. 485

The solutions were degasscd with a glass-frit bubbler for 13 min with nitrogen before each titration and continously during the titration. l’hc titr,ant was ncldcd in r-ml increments before the end-point region and o.z-ml increments in and after the end-point region. In all titrations, cxccpt the last three sets of data whcrc two minute intervals wcrc used, one minute intervals wcrc taken bctwccn atltlition of reagent and reading of current. ‘I’he constant potential was supplied by and tlrc current was read with the manual polarograph built at l
Pig.

The experimental References p. 485

results are given in Tables I and II.

4.

p;tl us. pll.

W.

484

f’UkC#L [lrequiv.)

-

I~ouud

5

98

~___

0.20

I

98.4 49.2 9.84 0.984

I M acctatc

o.rd$

ICN03

0.20

2 4 4 2 2

2

2

98.4 245.9

G

984.3

0.12

98.2

0.20

246.0

6 ___--___

4g.2

-----

--

983.6

5.0

_-

-.-_-_

._-

._____._~_.

0.

W

ii G 6 0

5

I

I .z

20 (1959)

IlUllcr

MJ)

980.

7’7.0 983.G 358.5 I 79.2

I

S./J.

(pcquiv.)

hl.

983.0

0.45

VOL.

1%. A. OSTERYOUh’G

o/

No.

_----------

983.6

0.50

S. I
0.40

48.9 _.___-..__

0.20

5.0 0.2lvf

acctatc

___------

;.:

5.0 .._---

‘I’hc cspcrimcntal results for the amperonlctric titration show that this titration can lx used to titrate from #.3.(i down to +Q ycccluiv. of 1SlXA in about 70 ml of solution wit11 copl)cr(l I) at tlic I<. 1’.1<. in an ncctatc buffer of pll 5.0 ‘I’licsc amounts correspond to a conccntrution range of 7*ro- 3 to 7~ro-GM ED’L’A. ‘I’hc results also show tlmt wllcn $5.4 /quiv. wcrc taken (7.ro-~dI IZD’I’A), a prr of 4.73 and 5.73 did not change tlic amount of EIITA found to a significant dcgrcc. Wllcn o.$Q /cccluiv. (7*x0-“.‘ll) of ED’I’A wore titrated in an acctatc buffer of pI-I 5.0, the a1110unt fOuJld clicl nut compare well with the amount taken bccausc tllc 15D’TA at this low concentration and at tllis per dots not complctcly con~ples tllc copper. ‘I‘lic stability constant, I<, for the funclatncntal reaction cu-t.2 wlicrc tntc

Cu+2 ion,

is tlic

coppcr(1

I) ion

stability

stability

y-4

Y-81,

q+ tlw

cuy-2 fully

ionized

cthylcnccliaminctctraacc-

is I<

The

and

-I_

constant

constant

at

for a

=

tlic

particular

(CuU-2)

/ (CU’~“)

(Y-s’).

is 10*o*H. Tlic apparent by dividing K by u, the as 1‘-al (and not as other dissociated states of

copper-EDTA pry

may

cornplcx

bc

calculatecl

fraction of EDTA which is present H,lY). U= I + (Ii+) / I<,, + (Ii+)” / KJ& + (H+)3 / K4Ii3K3 + K4, K3, Ka, and Kr arc the acidity constants of ED’I’A. ILzferemes p.

JY5

(H+)*i / K&oKaK1

wllcrc

VOL.

20 (1959)

AMPEROMETRY

AND

POTENTIOhfETRY

OF

EDTA

WITH

cu(II)

485

Since a concentration less than about 7*x0-5M EDTA could not be titrated at a ” per of 5.0, the above equations were used to calculate a complexcd copper to uncomplcxed copper ratio, at the end-point, below which the titration would not go to completion. This ratio was found to bc IO ~1.Using this ratio, the mirlimum concentration of EDTA that could be titrated with copper(I1) (or vice ve~sa) at a given prr was determined for scvcral pi values. These values are plotted in Fig. 4 as log of minimum concentration, p&I, verszds prI. The experimental results for the potcntiometric titration at small constant current of ED’I’A with coppcr(II) at the R.P.E. show that this titration can be used to dctcrmine 9X3.6 to 49.2 Itcquiv. of ED’L’A in about 70 ml of solution (7*x0--3 to 3.5aIO-4:\f a kry sharp potential break of about 0.3 V occurred KIXA). In all cxpcrimcnts, at the end-point. An applied current of 5 ,M:\ may bc a little high for titrating below about 500 pucquiv. in 70 ml of solution since the amount of free copper(t I) required to give a diffusion current of this size is a little beyond the end-point ancl will be further beyond the end-point as the concentration of EDTA in solution is clecreascd in subsequent titrations. An applied current of r-z /LA is recommended. SUhlhlARY with copper was pcrfortncd in an acetate Tlic ampcronictric titration of 7. lo- GM JWTA bllffcr of pH 5.0 iItthe rOtntct\ ~kLtilllllll dcCtrO&. r\ pl r.lllgC Of 4.73 t0 5.73 U3.S UsCd t0 titratC ~-IO-4A3 EDTA. ‘I’lic potciitioinctric titration at ~n~all constant current of 7.10-3 to 3.5.10-4iI’r 131X.\ with coppcr(I I) wily pcrformctl in an Wctatc buffer of pn 5.0 at the rotated platinum clcctrcdc.

Url titrilgc ainp&~m&triquc ct un titrngc I)otclitioril6tricl~Ic dc l’acitlc dtliyl~ncdiaminotdtra ac&tiquc, par Ic cuivre(1 I). out dt& cffcctuh cn milieu tampon h 1’Clcctrode toiirnante de platinc.

ZUSAMRIENL~I\SSUNG Es wird cinc rrmpcronictrinclio und potcntiomctrischc Titration von Atliylcndiainiriotetracuuif+urc rnit Cu-(I 1) in gcpuffcrtcr LCIYUII~an ciner roticrcndcn Platiuclcktrodc bcscllricbcn.

1 R. PHI~~L AND 13. MATVSKA, Collecliott Crectioslov. C/tern. Cotnttiartis.. 16 (195x) 139. 2 tl. ACKERPIASN AND C. So~w,~~~zs~u,\crc, I;lelv.Clrirn. Acln. 35 (1952) 485. a C. N. REILLY, W. G. SCHIUNICR AND C. TEMPLE, Aml. Chew., 28 (1g50) Also. 4 N. 'rhNAK.4, &I. ~
Received

September

30 th, 1958