Spectrophotometric determination of Pd(Ii) with P-Dimethylaminebenzylidenerhodanine

Spectrophotometric Determination of Pd(Ii) With P-Dimethylaminebenzylidenerhodanine

Lucia Felicidade Dias^I; Jorge NozakiII^*

^IMestrado em Quimica Aplicada/UEM

^IIDepartamento de Quimica, Universidade Estadual de Maringa 87.020-900 Maringa, PR., Brazil

ABSTRACT

p-Dimethylaminebenzylidenerhodanine in methyl isobutyl ketone was employed as selective and sensitive reagent for the extraction and determination of palladium(II) in metal alloys and rocks. Beer’s Law is followed in the concentration range 0.2–2.4 m g.mL^-1 of organic phase with a molar absorptivity of 3.0x10⁴L.mol^-1.cm^-1. The detection limit observed for aqueous solution was 0.1 mg.L^-1. The extractions were performed at pH 2.4 and no interference of foreign ions such as Cu²⁺, Zn²⁺, Fe³⁺, Pb²⁺, Hg²⁺ ,etc., were observed in jewellery alloy and rock sample analyzed. The complex of reagent and palladium(II) was pH dependent and it should be carefully controlled during extraction. Continuous variation and mole ratio methods showed that the complex composition was 1:1.

Keywords: p-dimethylaminebenzylidenerhodanine; palladium(II); extraction-spectrophotometry; rocks; metal alloy

INTRODUCTION

The compound 5-(4-dimethylamine benzylidene) rhodanine (DMABR) and its derivatives are reagents that form very strong and stable complexes with platinum group elements (Pd²⁺, Au³⁺, Ag⁺, Ir³⁺ e Rh³⁺ ) in weak acidic media (Sandell, 1948), (Natelson and Zuckerman,1951), (Sandell and Numayer, 1951), (Narang and Ayres, 1961), (Doycheva et al.,1971), (Borissova et al., 1975), (Borissova,1975), (Pangarova, 1977), (El-Zawawy et al.,1995), (Borissova et al., 1975). The spectrophotometric method for the determination of Pd²⁺ with DMABR was first proposed to be performed in acidic media such as formic , hydrochloric , acetic and propionic acids (Narang and Ayres, 1961). It was observed that Au³⁺, Ir³⁺ and Cr(VI) were serious interfering ions, (especially gold). On the other hand, the interfering action of silver was easily masked by hydrochloric acid, removing the silver chloride formed.

Hydrochloric acid medium, pH 1.0, was used to the determination of Pd²⁺, without the interference of silver by Borissova et al.(1975). The determination of Pd²⁺ with DMABR was performed using the toxic nitrobenzene as solvent (Doycheva et al.,1971). It was also observed that Au³⁺ was a serious inteferent even in trace amounts, while ions such Fe³⁺, Bi³⁺, Pt⁴⁺, Hg²⁺ , Cu²⁺, Pb²⁺ , Cd²⁺, CN^-, etc., showed interfering actions only at larger concentrations.

In this paper, we report the results on selective extration of Pd²⁺ from aqueous solution, pH 2.4 , with DMABR in methyl isobutyl ketone (MIBK). The spectrophotometric determination of Pd²⁺ was performed directly in organic phase. The separation of Pd²⁺ and Au³⁺ was also investigated to be employed for samples with higher gold concentration.

MATERIALS AND METHODS

Reagents

The solution of DMABR (Aldrich-USA) 1,0x10^-4 mol.L^-1 was prepared in MIBK. The solution of Pd²⁺ (73,40 µg.mL^-1) was prepared from PdCl₂ (Aldrich-USA) and standardized by the Th(NO₃)₄-EDTA method (The Merck Index,1976). A solution of NaF (1.0 mol.L^-1) was employed as masking reagent of Fe³⁺, ethanolic solution of 0,25 mol.L^-1 dimethylglyoxime was used for Pd²⁺ and Au³⁺ separation, and a mixture of EDTA 0,100 mol.L^-1 with 1,2 mol.L^-1 sodium citrate as masking agent to the other ions such as Fe³⁺, Cu²⁺, Ca²⁺, Mg²⁺, Zn²⁺, Ni²⁺, etc.

Preparation of standard Pd²⁺ solution

Titration of a 50 mg.L^-1 of Th⁴⁺ as Th(NO₃)₄ solution, adjusted to pH 1.0-2.0 with HNO₃, was performed with 0.100 M EDTA to a xylenol orange end point, according to the reaction:

1.0 mL of 0.100 M EDTA solution = 23.204 mg of Th⁴⁺.

In the following step, 10.0 mL of 0.100 M EDTA(excess) were added to an acidic solution of ~50 mg of Pd, pH ~3.0, using xylenol orange as indicator. The back titration was performed with 0.100 M Th(NO₃)₄ , and the concentration was calculated using the following relationship:

1.0 mL of 0.100 M EDTA = 10.64 mg of Pd²⁺

Sample preparation

The pegmatite rock was collected from Campo Largo County, Parana State, Brazil. A rock sample with mineral veins and an average of 6.0 (Mohs’scale of hardness), irregular masses and grains of many sizes, specific gravity of ~ 2.7, where the presence of other minerals such as fluorite, feldspar, and chalcopyrite gave a grey-brown colour. The sample containing Si, Pd, Au, Fe, As, S, etc., was crushed to 100 mesh, heated at 800ºC for 3 h, and dissolved with aqua-regia. After filtration and separation of undissolved SiO₂, the pH was adjusted to 2.4. The liquid-liquid extraction were performed five times with 2.0 mL of 1.0 x10^-4 mol.L^-1 solution of DMABR in MIBK.

Extraction and Pd²⁺ determination

The optimum conditions for the extractions of the complex Pd²⁺:DMABR, such as pH of aqueous solution, reagent concentration, presence of interfering ions, etc., were investigated using a 125 mL separatory funnel. The Pd²⁺ from aqueous solution was extracted with 2.5 mL of DMABR and the organic phase was transferred to a 10.0 mL volumetric flask. The extractions were performed four more times using the same volume of DMABR. The spectrophotometer Beckman-DU-70 was used for absorbance reading with 10 mm cell at 502 nm. The stability of Pd²⁺-DMABR complex was investigated reading the absorbance in time intervals of 5 minutes during 90 minutes. The calibration curve was prepared changing the concentrations of Pd²⁺ in aqueous solution, using the same procedure for extraction and spectrophotometric determination.

Complex stoichiometry

The molar ratio and continuous variation methods (Skoog and Leary,1992) were employed for the determination of Pd²⁺:DMABR stoichiometry in MIBK. Volumetric flasks of 10.0 mL were used adjusting the pH to 2.4 , and reading the absorbance at 502 nm up to 60 minutes.

Interfering ions

The extraction efficiency of Pd²⁺ was investigated in the presence of several ions in aqueous solution, pH 2.4. To the standard solutions of Pd²⁺ (0.12 µg.mL^-1), several ions with known concentrations were added to investigate its interfering action on Pd²⁺-DMABR complex.

Separation of Pd²⁺ and Au³⁺

The separation of Pd²⁺ and Au³⁺ was investigated to be applied in samples with higher gold concentrations . To a 200 mL solution containing Au³⁺ , Pd²⁺ , Ni²⁺ , and Fe³⁺ , 0.5 mL of NaF, 1.5 mL of the mixture of EDTA-sodium citrate were added and the pH was adjusted to 5.5 with solutions of 0.1 M Na₂CO₃ and HCl . The solution was warmed at 60 – 70ºC and an alcoholic solution of dimethylglyoxime (DMG) was added drop by drop until complete precipitation of Pd²⁺. After digestion of the precipitate for 30 minutes at the same temperature, hot filtration was performed with 10-20 µm porosity Buchner funnel. The precipitate was washed three times with 0.1 M HCl and several times with distilled water. Aqua-regia (2 mL) was used to dissolve the precipitate, and the solution was heated to expel oxides of nitrogen. The residue was redissolved with 6 ml of 6 M HCl, diluted to ~90 ml with distilled water, the pH was adjusted to 2.4, and completed to the mark (100.0 ml) with distilled water. The selective extraction of Pd²⁺ was performed with DMABR and MIBK at this pH.

RESULTS AND DISCUSSION

Figure 1 shows the extraction efficiency of Pd²⁺ with DMABR as function of pH of aqueous phase. The concentrations used were: DMABR 1,0x10^-4 mol.L^-1 and Pd²⁺ 0,12 µg.mL^-1 in aqueous phase. Optimum pH range was 2.0 – 2.5 with maximum efficiency at pH 2.4. Figure 2 shows the stability for the complex Pd²⁺:DMABR in organic phase as function of time with absorbance reading at 502 nm. The complex was very stable for at least 60 minutes as shown in Figure 2.

The extractions were performed using a 125mL separatory funnel. The volume used of DMABR in MIBK were 2.5 mL and after four extractions the total volume were 10.0mL. The absorbances reading were at 502nm using 10mm cell. The following concentrations were used: DMABR = 1.0x10^-4 mol.L^-1 and Pd²⁺ = 0.12 µg.mL^-1.

The organic extract of Pd-DMABR complex were investigated for stability, reading the absorbances at 502nm in time intervals of 5 minutes during 90 minutes.

Table 1 shows the influence of several ions during the extraction of Pd²⁺:DMABR complex. Gold, silver and mercury were the main interfering ions in concentrations higher than 0.3 µg.mL^-1.

The analytical calibration curve showed that Beer’s Law was followed from 0.2 to 2.4 µg.mL^-1 of palladium in organic phase. The detection limit observed for aqueous phase was 0.1 µg.L^-1. Table 2 shows the spectrophotometric determination of Pd²⁺ in metal alloy and pegmatite sample of quartz vein, and also the determination by ICP-MS (Inductively coupled plasma atomic emission spectroscopy).

Using the selective extraction of Pd-DMABR complex in MIBK at pH 2.4, no interference was observed by Ni²⁺, Fe³⁺, Au³⁺ ,etc. The following conditions were used for ICP analysis: Spectrometer Baird PSX; 1.0 kwatts; integration time of 5 decseconds; argon flux 7.5 L.min^-1; auxiliary argon flux 1.2 Lmin^-1; sample introduction rate 1.2 mL.min^-1; nebulizer pressure 26 psi; and wavelength 340.458 nm. The 1:1 stoichiometry of Pd²⁺-DMABR complex were investigated by continuous variation and molar ratio methods as shown in Figures 3 and 4. The calculated formation constant K_f was 2.4 x 10⁵ according to Skoog and Leary (1992).

Tem volumetric flasks of 10.0mL were used to investigate the continuous variations method. The initial concentrations of Pd²⁺ and DMABR were 7.34 x 10^-5 mol.L^-1. The first flask shows that the volume proportion were 9.0mL of Pd(II) and 1.0mL of DMABR. In the stoichiometry ratio (1:1) the volumes proportions were 5.0mL of Pd²⁺ and 5.0mL of DMABR solutions, as shown in Figure 3.

The concentration of Pd²⁺ was 5.0x10^-5 mol.L^-1 keeping constant over the total experiment. The concentrations of ligand (DMABR) were variable and changed from 1.0x10^-5 mol.L^-1 to 9.0x10^-5 mol.L^-1.

CONCLUSIONS

The interfering action of gold and several ions were investigated and solved by the selective extraction of Pd-DMABR complex in MIBK at pH 2.4. Small amounts of gold in aqueous phase did not interfer during the extraction of Pd-DMABR complex in MIBK at pH 2.4. Samples with larger amounts of gold were separated after precipitation of Pd-DMG. The method investigated is very sensitive for palladium determination.

ACKNOWLEDGEMENTS

The authors would like to thank Brazilian National Council of Scientific and Technological Development (CNPq) by financial support, and Instituto Tecnológico do Paraná-TECPAR by ICP-MS determination of palladium.

Received: January 26, 1998,

Revised: June 01, 1998,

Accepted: October 28, 1998.

• Borissova,R.; Koeva, M. and Topalova, E.(1975), Predictions of conditions for use of spectrophotometric reagents: p-Dimethylaminobenzylidenerhodanine as a spectrophotometric reagent for silver and palladium.Talanta, 22, 791-796.
• Borissova, R.; Mosheva, P.; Ivanova, Z. and Topalova, E. (1975), Extraction-spectrophotometric determination of gold and palladium in materials of complex composition using p-Dimetylamino benzylidenerhodanine. Z.Anal. Chem.,Band 273, Heft 1.
• Borissova, R.(1975), Spectrophotometric determination of gold(III) with p-Dimethylaminobenzylidenerhodanine in hydrochloric acid-ethanol medium. Talanta, 22, 797-802.
• Doycheva,R.B.; Topalova,E.K. and Mosheva, P.A.(1971), Extraction-spectrophotometric determination of palladium(II) with p-Dimethylaminobenzylidenerhodanine (DMABR). Comptes rendus dedÁcademie Bulgare des Sciences, Tome 24, (12),1675-1678.
• El-Zawawy, F. M.; El-Shahat, M.F.; Mohamed, A.A. and Zaki, M. T. M. (1995), Spectrophotometric determination of silver and gold with 5-(2,4-Dihydroxybenzylidene) rhodanine and cationic surfactants. Analyst, 120,February,549-554.
• Narang, B. D. and Ayres, G. H. (1961), Spectrophotometric determination of palladium(II) with 5(p-imethylamino benzylidene)rhodanine. Analytica Chimica Acta, 24, 241-249.
• Natelson, S. and Zuckerman, J.L. (1951), Estimation of gold in biological materials.Anal. Chem.,23, (4), April, 653-655.
• Pangarova, R.B.; Mosheva, P.A. and Topalova, E. K.(1977), Sensitive-spectrophotometric method for the determination of rhodium(III) with p-Dimethylaminobenzylidene rhodanine (DMABR).Comptes rendus dedÁcademie Bulgare des Sciences, 30, (6),859-862.
• Sandell,E.B.(1948), Colorimetric determination of traces of gold.Anal. Chem.,20, (3), March, 253-256.
• Sandell, E. B. and Neumayer, J. J. (1951), Photometric determination of traces of silver. Anal. Chem., 23, (12), December 1863-1865.
• Skoog, D. A. and Leary, J. J. (1992), Principles of Instrumental Analysis. Saunders College Publishing. A Harcount Brace Jovanovich College Publisher, New York, pp.152-153.
• The Merck Index (1976), Ninth Edition, Merck & Co. Inc.,pp. 906-907.

*

Author for correspondence

Publication Dates

• Publication in this collection
  26 May 2011
• Date of issue
  1999

History

• Accepted
  28 Oct 1998
• Reviewed
  01 June 1998
• Received
  26 Jan 1998