Spectrophotometric determination of platinum metals

MICRDCHEMICAI

JOURNAL

28, lo- 19 (1983)

Spectrophotometric Platinum

Determination Metals

of

VII. Determination of Palladium with Bromopyrogallol Red and Pyrocatechol Violet J. EGERMAIEROVA,

L. ~ERMAKOVA,

AND V. SUK

INTRODUCTION An increased attention has recently been paid to spectrophotometric determinations of platinum metals (8) with dyes of various types, often in the presence of tensides that have a favorable effect on the coloration of the complexes formed (Y). In the present article, the reactions of Pd(I1) with two triphenylmethane dyes-bromopyrogallol red and pyrocatechol violet-were studied, following, also, the effect of a cationic tenside on these binary complex systems. Optimal conditions were found and procedures were developed for new spectrophotometric methods of determination of palladium. Although the reactions of bromopyrogallol red and pyrocatechol violet with numerous ions have been employed for spectrophotometric determinations of a number of metals, the platinum metals have not yet been determined with these dyes: a preliminary study has been carried out of the reaction of Pd(I1) with pyrocatechol violet (4). EXPERIMENTAL Spectrophotometric measurements were performed on an SP 800 Unicam recording spectrophotometer (Pye- Unicam Instruments Ltd., Cambridge, England) and on a Spekord instrument (VEB Carl Zeiss, Jena, German Democratic Republic) with l.OO-cm quartz cuvettes. The solution pH was measured with a GK 2401 B combined electrode and a PHM 24 pH-meter (Radiometer, Copenhagen, Denmark).

A 5 x 10-“-M stock solution of bromopyrogallol red (dibromopyrogallolsulphophthalein, DG) was prepared by dissolving 0.0288 g of the purified dye in 20 ml ethanol and diluting with distilled water to 100 ml. 10 0026-265X/83/010010-10$01.50/0 Copyrlpht

Cc), 19x3 by Academic

Preq\.

Inc

DETERMINATION

OF

PLATINUM

b1ETAI.S

11

The solutions used were not older than two days. The commercial preparation from Lachema, Brno, Czechoslovakia was used and was purified according to Vod&k and Leminger (13). A 5 x IO-%2 stock solution of pyrocatechol violet (PV) was prepared by dissolving 0.2162 g of the purified substance in distilled water in a IOOO-ml volumetric flask and diluting with water to the mark. The substance from Lachema, Brno, Czechoslovakia was purified by repeated crystallizations from 85’?? ethanol (6). A 5 x IO-“-M stock solution of cationic tenside Septonex (lcarbethoxypentadecyltrimethylammonium bromide (7, 9)) was prepared by dissolving 0.5281 g of the substance (Spofa, Prague, Czechoslovakia) in water in a 250-ml volumetric flask and diluting with distilled water to the mark. The purity of the substance satisfied the requirements of Czechoslovak Pharmacopoeia. A 1 x lO-:j-M stock solution of Pd(l1) was prepared by diluting a 10% solution of PdCl, p.a., containing 0.06 g Pd per milliliter (Safina, Vestec, Czechoslovakia), with distilled water containing a defined amount of Pd per milliliter (2) to a total volume of 100 ml. The solution pH was adjusted with the Walpole acetate buffer, Stir-ensen phosphate buffer (5). hydrochloric acid, and sodium hydroxide.

Defermitz~rfion of’Pd(ll) ,trirlr DG. Five milliliters acetate buffer (pH 5.6) and 2 ml 5 x 10pa-M DC are pipetted to a 25-ml volumetric flask, followed by a sample solution containing 10.0 to 75.0 pg Pd(I1). The flask is filled with distilled water to the mark and the solution is allowed to stand 40 min at laboratory temperature. The solution absorbance is then measured at 620 nm against the blank. Drrerminatiott of Pd(I1) ,c,irij DG in the presencr of‘ Septonex. Five milliliters acetate buffer (pH .5.0), 2 ml 5 x IO-‘-M DG, 2 ml 5 X 10-“-M Septonex, and the sample solution containing 10.0 to 65.0 pg Pd(II) are pipetted to a 25-m] volumetric flask. The flask is filled with distilled water to the mark and the absorbance is measured, after standing the solution 20 min at laboratory temperature, at 634 nm against the blank. Deter-tninution o.f Pd(lI) \citlt PV. Amounts of 5-ml phosphate buffer (pH 6.01, 4 ml 5 x 10-‘-M PV, and the sample solution containing 10.0 to 75.0 pg Pd(II) are added to a 25-ml volumetric flask, distilled water is added to the mark, the solution is set aside for 120 min at laboratory temperature, and the absorbance is measured at 650 (or 570) nm against the blank. Dt~~evminurion of Pd(II) )l’itlt PV in t/t<> pwsence o/’ Septnttc~x. Five milliliters phosphate buffer (pH 6.5), 4 ml 5 x IO-‘-M PV and 3.5 ml 5 x 10-‘:s-M Septonex are added to a 2S-ml volumetric flask. The sample solu-

12

EGERMAIEROV/i,

CiERMAKOV.4,

AND

SUK

tion containing 10.0 to 75.0 pg Pd(II1 is added, the flask is filled with distilled water to the mark, the solution is allowed to stand at laboratory temperature for 20 min, and the absorbance is measured against the blank at 700 nm. RESULTS

AND DISCUSSION

Palladium reacts with DG within a pH range of 5.6-6.2 with formation of complexes that are manifested in the visible absorption spectrum by pronounced decrease in the absorption maximum of the dye (h = 560 nm, Fig. I, curve 1) and its extension into the regions of longer and shorter wavelengths, reaching up to the uv region (Fig. 1, curve 2). For the

+

4 500 Wavelength

600

700

[nm]

Flc;. 1. Absorption spectra of Pd(Il)-DC and Pd(II)-DC-Septonex: c’,,~,= 2 x IO a M. (3) difference between (I) (‘I),; = 4 x 10~’ M. C’S< ,,,,l,,,ll\ = 4 x 10-l M. (I) DG, (2) Pd(II)-DG, and (2), (4) DG-Septonex. (5) Pd(II)-DC-Septonex, (6) difference between (4) and (5). (I) to (3): pH 5.6, measured after standing 40 min at laboratory temperature: (4) to (6): pH 5.0, measured after standing 20 min at laboratory temperature. Measured against water on a Unicam SP 800 instrument.

DETERMINATION

OF PI,ATINUM

METALS

13

measurement of the Pd(II)-DG binary complexes, the maximum of the difference curve was used at 620 nm (Fig. 1, curve 3). The maximum absorbance (at h = 620 nm, c,,,, = 2 x lo-” M) is attained, with the optimal pH of 5.6, for dye concentrations greater than 4 x lops M. i.e., for an at least two-fold excess of the dye over the metal; this absorbance value then remains constant at least to c,)(; = 7 x lo-” M. Complete coloration of the Pd(II)-DG complexes under the optimal conditions (pH 5.6: c,)(; = 4 x 10 ’ M; (‘,,(, = 2 x IO-: M; h = 620 nm) is attained after standing 40 min at laboratory temperature. The maximum absorbance of the complexes at 620 nm remains constant for 7 h and then slowly decreases. The solution color does not deepen after heating for 5 min to 40,60, or 80°C and the complexes decompose on heating to 100°C. The composition of the complexes formed was determined by the Job continuous variation method (c‘,,,,~,,= 6 x IO-” ,V, A = 620. 6.50, and 680 nm; pH 5.6) and metal-to-dye ratios of 1: 1 (A = 620 nm) and 1:2 (A = 680 nm) were obtained. The binary complexes formed can be used for the spectrophotometric determination of palladium: the corresponding characteristics and the suitable concentration range for palladium are given in Table 1. Table 2 contains the results of a statistical evaluation of the calibration plot. The effect of the other platinum metals on the determination of palladium and that of Au(II1) and Cu(I1) can be seen from Table 3. A study of the effect of some other ions has shown that Na-, K+, Cl-, and SO: do not interfere up to a Pd(II)-to-ion ratio of 1: 1000; NO; up to a ratio of 1:200, EDTA up to a ratio of 1:50, Mg’- up to 1:20, Co2+ up to I: 10, and Zn’+ up to 1:3 do not interfere. Fe”‘,, Pb’+, and Al”+ interfere. Addition of a third component, cation active tenside Septonex, to the colored binary Pd(II)-DG complex leads to a bathochromic and hyperchromic shift of the absorbance maximum (Fig. 1, curve 5). Septonex also TABLE 1 SPKTKOPHOTOMETRIC CHARACT~RIS-~ICS OF rot

Alilil\ System PdbDG Pd-DGSeptonex PdGPV Pd-PVSeptonex

Concentration range (pg ml ‘1

.s x lo-:’ (w.g cm 3

pH opt.

(nm)

5.6 5.0

620 634

1.8 1.96

0.41-3.19 0.41-2.66

10.02 S.50

6.0 6.5

6.50 700

1.51 3.45

0.41-3.72 0.41-3.19

7.21 3.11

the wavelength of the difference curve maximum; l ‘-molar absorption cvfor the difference curve maximum: S-sensitivity index: S = (c x lV(1000 x A).

Not<>. A,,,,,-

efficient

E’ x IO’ (I mol I cm-0

SYSTEMS STUDIED

14

EGERMAIEROVA,

CERMAKOVA,

AND SUK

TABLE 2 S’rATIsT1c.u

TREATMENT

System Pd-DG PdGDG-Septonex Pd-PV Pd-PV-Septonex

OF THE CALIBRATION

u

CURVES

b

0.0137 0.0213 0.0292 0.1416

0.0900 0.1676 IO.1222 0.2537

BY LINEAR

L,

0.0069 0.0250 0.0167 0.0042

REGRESSION

s0

s 1,

0.0025 0.0233 0.0130 0.0035

0.0045 0.0112 0.0048 0.0015

Note. b-regression straight line slope; u-regression straight line intercept, s,.,,-estimate of the standard deviation of the scatter around the regression straight line: s,,--standard deviation estimate for the determination of the regression coefficient; s,,-standard deviation estimate for the determination of the intercept.

shifts the optimal complex formation pH to more acidic values, from 5.6 to 5.0. The time required for complete coloration of the complex is shortened from 40 to 20 min at laboratory temperature. Heating of the reaction mixture to 40, 60, 80, and 100°C does not lead to an increase in the complex absorbance and thus the use of a higher temperature has no advantage. The absorbance at the maximum of the difference curve at A = 634 nm (Fig. 1, curve 6) remains constant for 8 h and then slowly decreases. The maximum absorbance at the optimum conditions (A = 634 nm; pH = 4 x 1O-4M) is attained for the dye = 5.0; cp<,= 2 x lo-” M; L’ser,t<,nex concentration c’,)(;= 4 x lo-” M and is constant within the interval c,)(; = 4 complex was to 8 x lo-” M. Further study of the Pd(II)-DG-Septonex carried out with cL1(;= 4 x lo-” M. The height of the absorbance maximum on the difference curve was followed under the optimal conditions in dependence on the Septonex TABLE 3 THE EFFECI

OF IONS ON THF. DETERMINATION

OF

Pd(l1)

WITH

DG”

Septonex Ion Os(lV) Rh(II1) Ir(IV) lr(II1) Pt(IV) Ru(II1) Cu(I1) Au(W)

Salt used (NH,),OsCl, RhCl:, (NH,),IrCI,, (NUlrCl, (NH,),PtCl, (NH,),Ru(H,O)Cl, CuSO,~5H,O AuCl,,.4H,O

Absent

Present

1:l I:5 5:1 I:2 1:l 1:l interferes* interferes”

1:2 I:5 5: 1 I:3 I:5 I:5 I:1 I:1

” The Pd(II):ion ratio at which the ion does not interfere. ’ Interferes at any ratio.

DETERMINATION

OF

PLATINUM

METALS

15

concentration and it was found that at cSer,tc,ne\ < 2 x lo-’ M turbidity is formed. Within the range of ~s,,,~,,,,,,from 2 X 10el to 5 x lOpAM, i.e., in the region of the formation of micellar aggregates of Septonex (.?), the absorbance is highest. For cseljtone,> 5 x IO-’ M the absorbance decreases with increasing Septonex concentration. The presence of the tenside also affects the dye alone: at a given pH, the dye absorption maximum shifts from 560 to 584 nm and the absorbance increases (Fig. 1, curve 4). A more detailed study has shown that the spectra of all anionic forms of the dyes change and these changes gradually increase with increasing tenside concentration (10, 12). Using the Job method in the presence of the cation active tenside in = 4 x 10~’ M) at wavelengths of h = 690,650, and 634 nm excess ((.Scr,lonrsx and with constant total concentration of the other components, c’~,,~>,, = 1 x 10e3M, the metal-to-dye ratio equal to I: 1 was found for all the above wavelengths. To verify this ratio, another method studying threecomponent systems (I) was used. However, this method was found unsuitable, because it requires a wide range of the component concentrations and, as stated above, turbidity is formed at low ratios of Septonex with respect to the other components, which prevents the measurement. The ternary micellar system, Pd(II)-DG-Septonex, can be used for the determination of Pd(I1); the spectrophotometric characteristics are given in Table 1 and the results of the statistical treatment of the calibration plot in Table 2. The effect of other ions on the determination of Pd(I1) in the presence of the cation active tenside is shown in Table 3, from which it follows that in the presence of the tenside greater amounts of Os(IV), Ir(III), Pt(IV), Ru(III), Cu(II), and Au(II1) are permissible. NO; does not interfere up to a ratio of I: 100 and the effect of other ions is the same as in the absence of the tenside. Rwction

of P&II)

M’ith PV

The binary complex of Pd(I1) with PV is formed at pH from 5.5 to 6.8. The formation of this olive green complex appears in the absorption spectrum as a decrease in the absorbance of the dye at A = 450 nm (Fig. 2, curve 1) and the formation of the characteristic plateau from 550 to 680 nm (Fig. 2, curve 2): the difference curve has the characteristic shape and attains a maximum at A = 650 nm. This wavelength was further used for \ the study of the Pd(II)-PV complex. The dependence of the difference curve maximum (A = 650 nm, cpcI= 2 x lo-” M) on the dye concentration shows that the highest absorbance is reached for c,,\ > 8 x IO-” M and this value remains constant at least up to c,>\’ = 1 x lo--1 M. The complete coloration of the Pd(II)-PV complex under the optimal

16

EGERMAImovA,

CERMAKOVA,

AND

SUK

t

400

450 Wavdength

500

GO0 b

700

800

I

FIG. 2. Absorption spectra of Pd(II)-PV and Pd(II)-PV-Septonex: c’,,~,= 2 x IO a M, cp\. = 5 x 10m5M ((1) to (3)); 8 x lo-” M ((4) to (6)), c~,>~,<,,~~~ = 7 x 1O-4M. (I) PV, (2) Pd(II)-PV, (3) difference between (I) and (2), (4) PV-Septonex, (5) PV-Pd(II)-Septonex, (6) difference between (4) and (5). (I) to (3): pH 6.0, measured after standing 120 min at laboratory temperature; (4) to (6): pH 6.5, measured after standing 20 min at laboratory temperature. Measured against water on a Spekord instrument.

conditions (pH 6.0; c,,v = 8 x lo-” M; c,,,, = 2 x lo-” M; A = 650 nm) takes as much as 120 min at laboratory temperature. The complex color is stable for 15 h and then the absorbance slowly decreases. Further measurements were thus carried out after this time from the solution mixing. An increase of the reaction mixture temperature (40, 60, 80, and 100°C) for 5 min does not lead to acceleration of the complex formation; on the contrary, discoloration occurs. The composition of the binary complexes obtained from the Job continuous variation method (ctola, = 1 x IO-” M; A = 620, 650, and 570 nm; pH 6.0) corresponds to metal-to-dye ratios of 1:2 (A = 620 and 650 nm) and 1:3 (X = 570 nm). The applicability of the colored Pd(II)-PV complexes to the determination of Pd(II) was further examined; the appropriate spectrophotometric characteristics are given in Tables 1 and 2. The effects of the other platinum metals on the determination of Pd(I1) are summarized in Table 4. Similar to DG, the effect of the cation active tenside was also followed for PV. Addition of Septonex to the dye alone causes a small decrease in the absorbance at X = 450 nm and appearance of a new pronounced

DETERMINATION

OF

TABLE

PLATINUM

17

META1.S

4

THE EFFECT OF I HE PLATINUM METAL IONS ON THE DETFRMINATION OF Pd(IU WITH PV” Septonex

-___~~ Ion OS(W) Rh(lIl) Ir(lV) IIfIII) Pt(IV) Ru(III)

Salt used (NH J20sCl,, RhCI,, (NHJJrCI,, (NH,):,IrCl,, (NH,),PtCI,, (NH,),Ru(H,O)CI,

Absent

___Present

s: I I:2 interferea” 4: I 5: I interferes”

S:I I:1 I:1 I:I s: I s: I

(I The Pd(lI):ion ratio at which the ion does not interfere. ‘j Interferes at any ratio.

maximum at A = 610 nm (Fig. 2, curve 4), which is characteristic of another dissociated form of the dye that normally appears only at higher pH values (pH > 6.5) (II). This effect confirms, similar to that found with DG, an influence of cation active tensides on the dissociation constants of triphenylmethane dyes. Addition of the cation active tenside to a solution of binary Pd(II)-PV complexes leads to development of a green-blue coloration that appears in the spectrum as a decrease in the absorbance at A = 450 nm, a pronounced deepening of the absorbance maximum at a wavelength around 600 nm (Fig. 2, curve 5) and a poorly perceptible maximum at higher wavelengths. The difference curve exhibits a pronounced maximum at about 670 to 750 nm (Fig. 2, curve 6): for further study of the complex formation, the difference curve maximum at 700 nm was used. In the presence of Septonex, the pH interval of the complex formation also shifts compared with that for the Pd(II)-PV binary complex to a value of 6.2 to 7.1. A value of 6.5 was further used as optimal. Complete coloration of the complex requires at least 20 min at laboratory temperature: then it is stable for at least 6 h and then slowly decreases. Heating of the reaction mixture does not improve the results, as discoloration occurs. The difference curve absorbance maximum (A = 700 nm; pH 6.5; c’,,~,= = 7 x 1Oe1M) slowly increases with increasing dye 2 x lo- 5 M; c~~,,~,,,,~~ concentration and remains constant for 7 x lo-; M < cpv < 1 x lo-* M. In further measurements, c ,,\ = 8 x lo-: M was used as optimal. The dependence of the difference curve absorbance maximum on the Septonex concentration under the optimal conditions shows that at cSer,toncX < 2 x lo-’ M turbidity appears, at cSe,,toneu c 3 x lo-” M the maximum growths, and from c~~.,,~~,,~, = 7 x lOpAM a constant value is attained up to at least I x IO-:’ M.

I8

EGERMAIEROVA,

CERMAKOVA,

AND

SUK

0

FIG. 3. Composition of the Pd(lI)-PV-Septonex complex obtained by the Babko method: clola, = I x IO-” M; pH 6.5; A = 700 nm; measured after standing 20 min at laboratory temperature.

The composition of the complex formed was determined by two methods: the Job continuous variation method in the presence of excess Septonex and the Babko method. The latter method (Fig. 3) yielded the ratio of the components in the Pd(II)-PV-Septonex ternary system of 1: 1:2: the former method gave more complicated ratios (1: I, 1:2, A = 660, 700, and 620 nm, clotal = 1 x lo-’ M). The reactions of palladium with PV in the presence and absence of the tenside were also used for the spectrophotometric determination of Pd(I1): the appropriate characteristics are given in Tables 1 and 2 and compared with those obtained for bromopyrogallol red. The effects of the other platinum metals on the determination of Pd(II) are summarized in Table 4. SUMMARY Optimum conditions were found for the reaction of Pd(iI) with two triphenylmethane dyes, bromopyrogallol red and pyrocatechol violet, and the effect of a cation active tenside, Septonex, on these reactions was investigated. On this basis, new sensitive spectrophotometric determinations of palladium were developed and evaluated and the effect of other ions was estimated.

REFERENCES I. Babko, A. K., “Fiziko-Khimicheskii Analiz Kompleksnykh Syedinenii v Rastvorakh.” Izd. Akad. Nauk USSR, Kiev, 1955. 2. cerm8kov8, L., Fantova, I., and Suk, V., Spectrophotometric determination of platinum metals. V. Determination of palladium with pyrogallol red. Chem. Z\se.sri 34, 357-363 (1980). S. CermBkova, L., RosendorfovB, J., and Makit, M., Determination of critical micelle concentration of I-carbethoxypentadecyltrimethylammonium bromide. Co//rc,f. Cxdr. Chrrrr. Corrrmu/~. 45, 21OG213 (1980).

DETERMINATION 4.

Chernova, E. G.,

R. K.. Kharlamova, Various

ligand

OF

PLATIhUM

L. N., Belousova.

complexes

of some

V. V.. Kulapina, elements

19

MEl-ALS

with

E. G., and Sumina,

pyrocytechol

violet

and

cetylpyridinium chloride. Zh. And. i(ltir?~. 33, 858-863 (1978). [in Russian] 5. Cihahk. J., Dvorak. J., and Suk. V.. “pH Measurement Handbook.” SNTL. Prague. 1975. [in Czech] 6. Foch, P., Study of the ternary complex of aluminum. pyrocatechol violet and cetylpyridinium bromide. Unpublished results. 7. Jurkevicidte, J., and Malat. M.. Study of the interaction of scandium and chromazurol S with cetylpyridinium, cetyltrimethylammonium or carbethoxypentadecyltrimethylammonium bromide. C‘o//~~c~r. C‘:ec/r. Cltcktt. C‘o,rt,rt/,/r. 44, 3236 3740 (1979). H. Marczenko.

Z.. “Spectrophotometric Determination of the Elements.” HorwoodWiley, New York. 1976. Y. Miillerova. A.. and Cermakova, L.. Spectrophotometric determination of the platinum metals. VI. The determination of rhodium and palladium with 4-7-(?-thiazolylazo) \ resorcinol in the presence of cation active tensides. C‘/~c,,!r. Zr,e.\(i. 3.5, 651 (1981).

10.

II. /2. 13.

Rosendorfova, J., and Cermakova, I,.. Spectrophotometric study of the interaction of some triphenylmethane dyes and l-carbethoxypentadecyltrimethylammonium bromide. T~~/~l,trtr 27, 7055708 (1980). Ryba. 0.. Cifka, J.. Malat, M.. and Suk. V.. Chemical indicators. II. Dissociation constants of pyrocatechol v,iolet. C/ro,r. I~i.cf~ 49, 1786 1791 (1955). [in Czech] Skarydova. V., and Cermakova. L.. Spectrophotometric study of tensides with 1.triphenylmethane dyes. C‘r,//(,c,/. C.:c(,/,. C‘/IC,,,I. C’~~~~t,rrlrrt. 47. 776 ( 1982). Vodak. Z., and Leminger. 0.. Sulphophthalein indicators. C/rc,/rt. Prll,rr. 5,7-l:! (1955). [in Czech]