224 Ah’ALY’lTCA CHIMICA ACTA

COMPLEX FORMATION AND FLUORESCENCE

PART IV. 8-QUINOLINOL-5-SUL,T;ONIC d\CII> AS A ‘I’I.‘TRAN’T I~OR nrvAr,rswr CATIONS

JOHN A. 13ISHOP

Newuvk College of Engineeviq, Newruk, N. J. (U..q.A.)

’ (Reccivcd July zest, 19G5)

During the course of work previously rcportcdr~3, it was observed that oxicla- tion of the reagent (as indicated by darlccning of solutions on standing) clicl not take place in solutions in which 8-quinolinol-s-sulfonic acid (OxSO3) was complexcd by cations, E:AroN3 has commented on this in the cast of other phenols, Rcpeatccl stan- dardizations during the present investigation showed a change in one Mg(OxS03)3 standard solution from 1.87 - x0-3 M to x.90 . x0-:) M with respect to OxSO3.

The formation constants shown in Table I indicate that it should bc possible to use a solution of Mg(OxSO3)3 as a titrant in a rcplaccmcnt titration, the appearance of fluorescence from the excess of rcagcnt being taken as the end-point. Preliminary tests showed that this could be followed best by an instrumental method, using a procedure similar to that used in photometric titrations”.

TRBLB I

FORMATION CONSTANTS OF OXSOn COhll’LIESl?S R

--.------_..-._-. .-- -.. .-__ .- .,.__ -_-_ . .._ . -

Cntiou Log I<, 1.06 K2 n!lr_, fIlloI’l!SCRIlC~! _---.__.__- _...-.. . .-.. .__.__. .- _.._.. . . .,__. _ ._ _-

MIZ 4.8 3.7 Yes Mn(T1) f>.G 4.9 No Cd 7.6 5.9 YCR l’c([ I) 8..$ 6.7 No %n 8.4 6.7 Yes 1%(11) 8.5 7.6 No Co(LI) Q.? 7.6 No Ni IO a.1 No cu 12.5 10.6 No __-.-- _-_--___ ._--_.- _..- - ..--_..-- .._ - __. R Vnlucv of tllc formation constants taken from rd. 5.

It has been rcportccl 1.0 that the fluorescence of Mg(OxSO3)a is at a maximum about PH 7 and decreases above PH 8. Since the other cations are more strongly com- plexed than magnesium, it is to be cxpccted that the end-point of the overall reaction

M(H) + M&O&03) 3~M(OxS03)3+Mg(II) (1)

should be observed best over this range of pi (7 to 8).

Anal. claim. Acta, 35 (1966) 224-230

~-QUIN~LIN~L-~-SULF~NIC ACID AS A TITRANT 225

EXI’ERILIENTAL

Reagents Magnesiwrt 8-quinolinol-pszrtfo22ate. This was prepared by weighingout enough

8-quinolinol+sulfonic acid (obtained from the Eastman Kodak Co. and used without further purification) to make the final concentration about 2 * x0-3 M, and dissolving in water containing enough magnesium sulfate to give a 10-3 M solution. To this solution was added I g phosphate buffer per liter to give PH 7. It is not necessary for the ratio of OxSO to Mg to be exactly 2: I but it should not be less than I: I and oxidation of uncomplexed OxSO may take place if it is greater than 2 : I. The titrant

solution was dispensed from a McClosky buret, with divisions of 0.02 ml. This arrange- ment gave a closed system, air being admitted only during a titration.

The other chemicals used were reagent-grade nitrates, with the exception of copper sulfate, and in the casesof Hg(II), Pd(I1) and Pt(lI). Both HgC12 and Hg(NO3)s were used with equally good results. I’dCls and I<zPtCL were obtained from A.D. Mackay, Inc., New York, N.Y. Solutions of approximately x0-3 M were prepared from more concentrated solutions, and the diluted solutions used in the titrations.

The concentrations on which the fluorescence was actually measured were about x0-6 M. A small crystal of sodium sulfite was added to the it-on(II) and the man- ganese(H) solutions to prcvcnt air oxidation of these solutions.

The 0xS0:~ solutions were standardized against coppeE sulfate hcptahydrate. The ratio of the formation constants of the copper and magnesium complexes is such that thcrc is no doubt of the completeness of the reaction.

Fluorescence measuvelrtc?2ts Thcsc were made using the Farrand Spectrofluorimeter which has been de-

scribed previously 1. The incident beam for excitation of fluorescence was set at 365 rnp and a filter to cut off stray light was used after the sample. The peak wavelength for the magnesium complex was at 495 rnp and for the zinc and cadmium complexes at 5~5 m,u. When both magnesium and zinc complexes fluoresced (as in the last por- tion of the expcrimcnts of Figs. 5 and 6) the peak “broadened” to extend from 5x5 to 495 mp. Fluorescent measurements were also made on some of the solutions using a Turner Model 1x0 Fluorimetcr with results similar to those shown.

Titration firocedzrre Titrations wet-c carried out by pipetting a fixed volume of the cation solution

into a roo-ml volumetric flask, and adding varying volumes of the titrant. The solu- tion was made up to IOO ml and the fluorescence measured about I h after mixing. The fluorescence was measured again after the solutions had been standing overnight. There was no significant change, indicating that the replacement reaction was a rapid one.

DISCUSSION

End-point phenomena in compleximetric titrations have been discussed by

.d?ral. Ckirn. Acta, 35 (1966) 224-230

226 J. A, BISHOP

other investigators 4~7-0, but they have restricted themselves experimentally to sys- tems involving I :I complexes. In the present series of experiments, two possible complexes of each cation had to be considered. Calculations on the effect of pH on the extent of complexation showed that all of the cations studied were essentially com- plexed to form M(OxSO& at PH 7. Some MOxS03 complex will be formed, however, when the ratio of total cation to complexing agent is I : I, which is the case at the end- point of all the titrations discussed in this paper. For two cations, M and M’, the following equilibria must be taken into account (L= ligand)

MLz+M’ = ML-tM’L (2)

K’ = (ML) (M’L) KUWL)

(MLz)(M’) = Icz(nrLa) (3)

ML+M’L =M’Lz+M (4)

I(” =: (M’L) (M) Ko(wL3)

(ML)(M’L) = Krcnrx.) (51

where ICI and Ka are formation constants. At the equivalence point, it may be assumed that

(M’) = (ML2)

(ML) = (M’L)

160 40 r

ml OxSO

Fig. I. Titration of Cu. Ni and Co with tiIg(OXS03)a vs. 8.89 * 10-3 M OxSO0. (x), I ml 0.0100 M Cu(I1): (o), I ml 0.0100 M Ni(I1); (A), I ml 0.0103 M Co(I1).

Fig. 2. Titration of Fe(I1) with Mg(OxSO&. (x), 5 ml Fc(I1) vs. 1.87 * 10-3 M OXSOS; MOB,,) = 1.87. 10-3. ( o), 2 ml Fc(I1) US. 1.87 * x0-3 M OXSOJ; M(F,,) = x.92 - x0-3. These results give an indication of reproducibility.

Anal. Chim. Acta, 35 (Ig66)~z2.+-o3o

8-QUINOLINOL-5-SULFONIC ACID AS A TITRANT 227

(M’La) = (M)

The ligand will be distributed as follows

XL = MLz+ML+M’L+M’Ls

(8)

(9)

Substituting from eqns.(s), (5). (G), (7) and (8)

E L = ML [(r/(1”) ‘) + 2 + (K”) ‘1 (10)

With Mg(OxSO& as titrant (MLs), and substituting values for the constants cal- culated from Table I, it was found that for the bivalent cations forming non-fluorcsc- ing complexes the percentages of titrated cation in the form of M’Ls were as follows: Cugg.4;Nig6;Cog3;Fe82;Mn35.

The experimental results justify the assumptions made, as shown in Figs. 1-3. Figure 4 shows the titration of mercury(I1) by Mg(OxSO&. No constant for the for- mation of mercury(I1) complexes with OxSO has been reported, but a comparison of its titration curve with Figs. z and 3 would indicate values in the neighborhood of those for the manganesc(I1) complexes.

60

ml OxSO

1 J( , 5 10 15

mlOxS03

Fig. 3. Titration of h!n(lI) with Mg(OxSO& 5 ml Mn(II) VS. x.87 * 10~~ M O~SO:,; Mm”) = 0.74 ’ 10-S.

Fig. 4. Titration of Hg(I1) with Mg(OxSO~)~. 5 ml Hg(NO& us. 1.87 - 10~~ M OxSoo; Mww = x.26* 10-S.

In Fig. I, the difference in the slopes of the Mg(OxSOs)e after the end-point is probably due to differences in light absorption of the copper, nickel and cobalt complexes. The copper and nickel complexes are different shades of green, while the cobalt complex has a pink tinge. The light absorbed is thus probably due to the emitted fluorescence, but it might be due to variation in the absorption of the exciting light.

In the cases of the manganese(II), iron and mercury(I1) curves, the rise of

Anal. C/rim. Ada, 35 (1966) 224-230

the curves above the base line as the end-point is approached, is a measure of the in- completeness of the reaction involved. As in the cast of photometric titrations, this does not prevent the determination of the equivalence point by extrapolation, which explains why this method is more universal as an instrumental method. Copper( which is very strongly complexed compared to magnesium, can be titrated very accurately visually, using a “blacklitc” in a dark room.

When eqns. (3) and (5) wet-c applied to the Cu-Zn, Zn-Mn, and Mn-Mg pairs, and the same assumptions were made as before, it was possible to construct Table II to show the possibility of titrating a solution containing Cu. Zn and Mn(II) with Mg(OxS03)~. Experimental results for this titration are shown in IQ. 5.

Figure 6 shows the results obtained when solutions containing Cu, Zn and Hg(I1) were titrated with Mg(OxSOs):!.

60

I I I

5 10 15 mlOxSO3

60

- . L/k___ L.._L-

5 10 15 20 ml OxOS3

ITig. 5. Titrationof Cu. Zn nnclMn(l I) inoncsolution. 3 1111 Cu -b 3 ml %n -I- 3 mlMn(l1) vs. 1.33 . 10-n M 0~60s. Sanw Znsolution as in l:ig. 6, cliffcrcnt Cu Yolution. CII = 0.55. I o-3 M; %n = 0.55 . x0-3 M; Mn = I..~Q * x0-3 IV.

ExCI~IANGlc CONSTANTS OF OsSOn COnIl~I.ESLSs

G- __-- - .-..- .._-.-_-. --.-- . . _ ..-.... -.- _-.. . __..___..., ._ ..-. .._ . . ..- __._

IV’ Log Ii’ Lob I<” n/o iI‘lL RI cquivalc~~ce paid

-_.-_ ___. ̂ _.._. --.. _._- -.-- .._.__- .._.._. .._. - .._._._ .._ - ..- __.._ ---.--__.-_ _..

CL1 Zn -2.2 -_5.8

%n 87

Mn -0.1 --3.5 Mn

35 MS -0.1 - 2.9 35

---- _._.____-________._ _. __--- ..-._ -_. __.__

Inspection of Figs. 5 and 6 indicates that the titration of Cu and Zn (or Cu and Cd) in the same solution can be carried out easily, but that the titration of 3 cations using Mg(OxSOa):! was feasible only when the cation with its formation constants closest to those of the magnesium complexes was present in relatively large amount.

Anal. Chim. Acta, 35 (1966) 224-230

8-QWNOLIXOL-5-SULFONIC ACID AS A TITRANT 32 9

It is also apparent that it should bc possible to titrate a mixture of copper and zinc using a solution containing Hg(OxSOs)?.

Figure 7 shows the result of such a titration, along with the titration of a copper-cadmium mixture using the same titrating solution. In these titrations the same volumes of copper solution were used, along with the same volumes of zinc and cadmium solutions which had slightly different concentrations. The copper solution was used as an internal standard.

Of the bivalent cations, barium and calcium are less strongly complexed than magnesium and therefore cannot bc titrated. Attempts to titrate palladium(I1) and platinum(I1) were unsuccessful, possibly due to strong complexing of these ions with chloride. The constants given for lead in Table I indicate that this complex should

5 10 mlOxSO:,

Fig. 7. Titrations of mixtures using Hg(OxS01)z (not fluorcsccnt) MC” = 0.07. 10-a M (usccl as standard) to give M0~80~ = I.53 - 10-a. x = Cu $- Ccl solution; lcfc,l = 0.82. x0-3. 0 = Cu + Zn solution: Man = 0.67 . x0-3,

form and that lead should bc titratable. However, the titration of this ion was not successful, nor was the titration of tin(II). Since both of the&c ions form strong hydroxy complexes, it is possible that mixed complexes were formed. Beryllium also could not be titrated.

SUhf hi AR\

S-Quinolinol-5-sulfonic acid can be used in compleximetric titrations by means of a displacement type of titration ; a fluorescent weak complex is used to titrate an ion which forms a non-fluorescing stronger complex, the end-point being the appear- ance of fluorescence. The titration is best performed by an instrumental method. A non-fluorescing weak complex can similarily be used for the titration of a cation which is strongly complexed and fluoresces, By making use of suitable combinations, it is possible to titrate a non-fluorescing complex former and a fluorescing complex former in the same solution.

~frrd. c/riw. ~Cfa, 35 (IgG6) 224-230

230 J. A. BISHOP

RIkUMIk

L’acide hydroxy-S-quinol6ine sulfonique-5 peut Ctre utilisd pour des titrages complexim&riques par d&placement: un complexe fluorescent, faible, est utilisC pour titrer un ion formant un complexc non-fluorescent plus fort. L’apparition dela fluores- cence indique le point final clu titrage. L’inverse est Cgalemcnt possible. On peut ainsi combiner le titrage d’un complcxc non fluorescent avcc cclui d’un complexe fluores- cent, dans une meme solution.

ZUSAMMENFASSUNG

8-Hydroxychinolin-5-sulfonstiure kann bei komplexometrischen Titrationen in Form einer Vcrdrtingungstitration verwendet werden. Es wird ein fluoreszierender schwacher Kamplcx vcrwendct urn tin Ion, welches einen nichtfluoreszierenden starkeren Komplex bildct, zu titriercn ; der Endpunkt zcigt sich durch das Auftreten von Fluoreszenz an. Die Titration 1Bsst sich sehr gut mit eincr instrumentellen Metho- de durchfiihren. En nichtfluoreszicrendcr schwacher Komplex kann in Shnlicher Weise fiir die Titration tines Kations verwendct werden, welches durch einen starken Komplex gebunden wird uncl fluorcsziert. Durch giinstige Kombination ist es mtiiglich, eincn nichtfluoreszierendcn Komplexbildner und einen fluoreszicrenden Komplex- bildner in derselben L&sung zu titrieren.

REl%RlSNCES

I J. A. 131s~~or~, .4ud. Chi~~t. Acts. zg (1963) I 72. 2 J, A. BISIIOP, /ItraC. Chim Attn. 29 (19G3) I 78. 3 D. IL EATON, Inovg. Chetn., 3 (19154) 1268. 4 J, U. HEADRIDGE, Pirolomelvic Tilvdions. Ch. 5, Pcrgamon Press, Oxford, England, IgGx. 5 J. BJIZRRUM, G. SCIIWARZBN~ACM AND L. G. SILLBN, Shbilify Coustanls, Vol. I, The Chc~nical

Society, London, Englantl, 1957, p. Gg. 6 D. MACDOUGALL, Paper prcscntccl at the IUPAC Cozrgress, 1961, Motrtveal, Canudu, See. C-3. 7 E.. WANNINBN, Talmrtu, 8 (~961) 355. 8 H. FLASCHKA, TaCadn. 8 (IQGI) 381. g M. TANAKA AND G. NAGAKAWA, AIral. Cirirn. Acfa, 32 (1905) 123.

/Illal. Chim. Ackz, 3.5 (Ig66) 224-230