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Environmental problems - Chemical approaches
RESEARCH ARTICLE

Capillary electrophoresis facilitates determination of metal complex stoichiometry by Job’s method of continuous variation

Nathan E. Boland A B and Alan T. Stone A

A Department of Geography and Environmental Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.

B Corresponding author. Present address: Whitman College, Hall of Science, 345 Boyer Avenue, Walla Walla, WA 99362, USA. Email: bolandne@whitman.edu

Environmental Chemistry 10(5) 409-416 https://doi.org/10.1071/EN13103
Submitted: 5 June 2013  Accepted: 5 September 2013   Published: 25 October 2013

Environmental context. Knowledge of metal-chelating agent speciation is integral to our ability to predict and interpret the behaviour of synthetic chelating agents in the environment. Capillary electrophoresis can be used to separate metal–ligand complexes with similar spectroscopic characteristics but different stoichiometries, thereby providing insight into metal–ligand speciation that is not possible by any other technique. Here, we demonstrate the utility of capillary electrophoresis for the determination of metal–ligand stoichiometries and evaluate its limitations.

Abstract. Job’s method of continuous variation is a traditional method used to determine the stoichiometry of metal–ligand complexes. The method is often applied to whole-sample absorbance measurements but its utility is limited when two or more complexes are present at significant concentrations and have similar absorption spectra. Here we employ capillary electrophoresis (CE), which separates complexes on the basis of charge and hydrodynamic radii, to extend the capabilities of Job’s method. Solutions containing nickel(II) and diethylenetriaminepentaacetic acid (DTPA) yield three CE peaks. Job’s method plot maxima, based on areas for each of the three CE peaks, coincide with nickel(II)-to-DTPA ratios of 1 : 1 and 1 : 2, which correspond to two complexes previously identified using whole-sample measurements, plus a ratio of 3 : 2, which corresponds to a previously unreported complex. We demonstrate how CE peak areas and electromigration times can be used to determine complex stoichiometries and formation constants. We discuss the strengths and weaknesses of Job’s Method coupled with CE and implications for speciation determination in environmentally relevant systems.

Additional keywords: chelating agent, diethylenetriaminepentaacetic acid, equilibrium speciation, nickel(II), polynuclear complex.


References

[1]  C. K. Schmidt, H.-J. Brauch, Occurrence, fate and relevance of aminopolycarboxylate chelating agents in the Rhine Basin, Germany, in Handbook of Environmental Chemistry 2006, vol. 5L, pp. 211–234 (Springer: Berlin).

[2]  M. Sillanpää, M. Orama, J. Rämö, A. Oikari, The importance of ligand speciation in environmental research: a case study. Sci. Total Environ. 2001, 267, 23.
The importance of ligand speciation in environmental research: a case study.CrossRef | 11286213PubMed | open url image1

[3]  B. Nowack, Environmental chemistry of aminopolycarboxylate chelating agents. Environ. Sci. Technol. 2002, 36, 4009.
Environmental chemistry of aminopolycarboxylate chelating agents.CrossRef | 1:CAS:528:DC%2BD38Xms1Omt7o%3D&md5=5fc9549eab1619fc9d043855aba99671CAS | 12380068PubMed | open url image1

[4]  F. G. Kari, S. Hilger, S. Canonica, Determination of the reaction quantum yield for the photochemical degradation of FeIII–EDTA: implications for the environmental fate of EDTA in surface waters. Environ. Sci. Technol. 1995, 29, 1008.
Determination of the reaction quantum yield for the photochemical degradation of FeIII–EDTA: implications for the environmental fate of EDTA in surface waters.CrossRef | 1:CAS:528:DyaK2MXktFeit7s%3D&md5=fbee780ca42a94997cab0b70d452b553CAS | 22176409PubMed | open url image1

[5]  P. Natarajan, J. F. Endicott, Photoredox behavior of transition metal–ethylenediaminetetraacetate complexes. Comparison of some group VIII metals. J. Phys. Chem. 1973, 77, 2049.
Photoredox behavior of transition metal–ethylenediaminetetraacetate complexes. Comparison of some group VIII metals.CrossRef | 1:CAS:528:DyaE3sXltFShtrw%3D&md5=f735d85472b34b75833d26e1197feb15CAS | open url image1

[6]  J. A. Davis, D. B. Kent, J. A. Coston, K. M. Hess, J. L. Joye, Multispecies reactive tracer test in an aquifer with spatially variable chemical conditions. Water Resour. 2000, 36, 119.
Multispecies reactive tracer test in an aquifer with spatially variable chemical conditions.CrossRef | 1:CAS:528:DC%2BD3cXhslWiurg%3D&md5=485254fbe8346612aa3f5bf3a91a4753CAS | open url image1

[7]  L. Helm, A. E. Merbach, Inorganic and bioinorganic solvent exchange mechanisms. Chem. Rev. 2005, 105, 1923.
Inorganic and bioinorganic solvent exchange mechanisms.CrossRef | 1:CAS:528:DC%2BD2MXivV2msrg%3D&md5=f4da7d5d675720ed96295047f1efe814CAS | 15941206PubMed | open url image1

[8]  D. L. Sedlak, J. T. Phinney, W. W. Bedsworth, Strongly complexed Cu and Ni in wastewater effluents and surface runoff. Environ. Sci. Technol. 1997, 31, 3010.
Strongly complexed Cu and Ni in wastewater effluents and surface runoff.CrossRef | 1:CAS:528:DyaK2sXlsFymtLc%3D&md5=557ffa33df3e1f2a1511267f63eae135CAS | open url image1

[9]  M. Bucheli-Witschel, T. Egli, Environmental fate and microbial degradation of aminopolycarboxylic acids. FEMS Microbiol. Rev. 2001, 25, 69.
Environmental fate and microbial degradation of aminopolycarboxylic acids.CrossRef | 1:CAS:528:DC%2BD3MXitl2lsg%3D%3D&md5=1e38f57ba490ea00c2c6ae9bfc309946CAS | 11152941PubMed | open url image1

[10]  M. Sillanpää, Comlexing agents in waste water effluents of six Finnish pulp and paper mills. Chemosphere 1996, 33, 293.
Comlexing agents in waste water effluents of six Finnish pulp and paper mills.CrossRef | open url image1

[11]  H.-B. Lee, T. E. Peart, K. L. E. Kaiser, Determination of nitrilotriacetic, ethylenediaminetetraacetic and diethylenetriaminepentaacetic acids in sewage treatment plant and paper mill effluents. J. Chromatogr. A 1996, 738, 91.
Determination of nitrilotriacetic, ethylenediaminetetraacetic and diethylenetriaminepentaacetic acids in sewage treatment plant and paper mill effluents.CrossRef | 1:CAS:528:DyaK28Xjs1Wmtr8%3D&md5=5e1b1975adb4c3c79ee3e9842435221cCAS | open url image1

[12]  C. K. Schmidt, M. Fleig, F. Sacher, H.-J. Brauch, Occurrence of aminopolycarboxylates in the aquatic environment of Germany. Environ. Pollut. 2004, 131, 107.
Occurrence of aminopolycarboxylates in the aquatic environment of Germany.CrossRef | 1:CAS:528:DC%2BD2cXltVOht7o%3D&md5=86a4f1f98566552a20cab9aaaeac4fe2CAS | 15210280PubMed | open url image1

[13]  P. Job, Formation and stability of inorganic complexes in solution. Annales de Chimie 1928, 9, 113.
| 1:CAS:528:DyaB1cXhvVWgsQ%3D%3D&md5=f00c55a16cddc457543cc5ce9288d132CAS | open url image1

[14]  P. MacCarthy, Simplified experimental route for obtaining Job’s curves. Anal. Chem. 1978, 50, 2165.
Simplified experimental route for obtaining Job’s curves.CrossRef | 1:CAS:528:DyaE1cXmt1Wrsro%3D&md5=7a1299dd044b83ef4cbd6f01559cd63eCAS | open url image1

[15]  W. Likussar, D. F. Boltz, Theory of continuous variations plots and a new method for spectrophotometric determination of extraction and formation constants. Anal. Chem. 1971, 43, 1265.
Theory of continuous variations plots and a new method for spectrophotometric determination of extraction and formation constants.CrossRef | 1:CAS:528:DyaE3MXkvVSqs74%3D&md5=c79d258ada652aa2219057e0920cc0e0CAS | open url image1

[16]  M. M. Jones, K. K. Innes, Restrictions on the use of Job’s Method. J. Phys. Chem. 1958, 62, 1005.
Restrictions on the use of Job’s Method.CrossRef | 1:CAS:528:DyaG1MXkslWg&md5=8d7db57772722b7f8a171520b20fd02aCAS | open url image1

[17]  M. M. Jones, The method of continuous variations for some special types of reaction. J. Am. Chem. Soc. 1959, 81, 4485.
The method of continuous variations for some special types of reaction.CrossRef | 1:CAS:528:DyaF3cXhsVOhsA%3D%3D&md5=3e6ad39c3c112b84910323388261a213CAS | open url image1

[18]  A. Simionato, M. Cantu, E. Carrilho, Characterization of metal–deferoxamine complexes by continuous variation method: a new approach using capillary zone electrophoresis. Microchem. J. 2006, 82, 214.
Characterization of metal–deferoxamine complexes by continuous variation method: a new approach using capillary zone electrophoresis.CrossRef | 1:CAS:528:DC%2BD28XislCnsbs%3D&md5=2da08376a0f95acb659523ea949bc2f8CAS | open url image1

[19]  R. K. Gould, W. C. Vosburgh, Complex ions. III. A study of some complex ions in solution by means of the spectrophotometer. J. Am. Chem. Soc. 1942, 64, 1630.
Complex ions. III. A study of some complex ions in solution by means of the spectrophotometer.CrossRef | 1:CAS:528:DyaH38XjsV2gsQ%3D%3D&md5=f980629358d17afd29cf7e7723443e17CAS | open url image1

[20]  W. Vosburgh, G. Cooper, Complex ions. I. The identification of complex ions in solution by spectrophotometric measurements. J. Am. Chem. Soc. 1941, 63, 437.
Complex ions. I. The identification of complex ions in solution by spectrophotometric measurements.CrossRef | 1:CAS:528:DyaH3MXhtlWntQ%3D%3D&md5=1c69ca339715b810a07a65f927ec7013CAS | open url image1

[21]  V. M. S. Gil, N. C. Oliveira, On the use of the method of continuous variations. J. Chem. Ed. 1990, 67, 473.
On the use of the method of continuous variations.CrossRef | 1:CAS:528:DyaK3cXkslOhtrs%3D&md5=cd01f44a3c310d84eba5dd46a389dcadCAS | open url image1

[22]  F. Woldbye, On the method of continuous variations. Acta Chem. Scand. 1955, 9, 299.
On the method of continuous variations.CrossRef | 1:CAS:528:DyaG2MXns1WhsQ%3D%3D&md5=cb4917d2f1d2dffeee2b8650d9edcba9CAS | open url image1

[23]  W. Buchberger, S. Mülleder, Determination of chelating agents and metal chelates by capillary zone electrophoresis. Mikrochim. Acta 1995, 119, 103.
Determination of chelating agents and metal chelates by capillary zone electrophoresis.CrossRef | 1:CAS:528:DyaK2MXosVyksr8%3D&md5=67054ac427f4d90a0b8b2809f98f5f8cCAS | open url image1

[24]  C. S. Bürgisser, A. T. Stone, Determination of EDTA, NTA, and other amino carboxylic acids and their CoII and CoIII complexes by capillary electrophoresis. Environ. Sci. Technol. 1997, 31, 2656.
Determination of EDTA, NTA, and other amino carboxylic acids and their CoII and CoIII complexes by capillary electrophoresis.CrossRef | open url image1

[25]  R. F. Carbonaro, A. T. Stone, Speciation of chromium(III) and cobalt(III) (amino)carboxylate complexes using capillary electrophoresis. Anal. Chem. 2005, 77, 155.
Speciation of chromium(III) and cobalt(III) (amino)carboxylate complexes using capillary electrophoresis.CrossRef | 1:CAS:528:DC%2BD2cXhtVSmtrfJ&md5=1d02f2537e2ffb236d4b134c6b610a1cCAS | 15623291PubMed | open url image1

[26]  P.-L. Laamanen, R. Matilainen, Determination of alternative and conventional chelating agents as copper(II) complexes by capillary zone electrophoresis–the first use of didecyldimethylammonium bromide as a flow reversal reagent. Anal. Chim. Acta 2007, 584, 136.
Determination of alternative and conventional chelating agents as copper(II) complexes by capillary zone electrophoresis–the first use of didecyldimethylammonium bromide as a flow reversal reagent.CrossRef | 1:CAS:528:DC%2BD2sXht1WgtLo%3D&md5=ded8ec03860ef589553c13c4b7d393a8CAS | 17386596PubMed | open url image1

[27]  D. R. Baker, Capillary Electrophoresis, 1st edn 1995 (Wiley: New York).

[28]  N. G. Connelly, T. Damhus, R. M. Hartshorn, A. T. Hutton, (Eds) Nomenclature of Inorganic Chemistry. IUPAC Recommendations 2005 2005 (The Royal Society of Chemistry: Cambridge, UK).

[29]  A. E. Martell, R. M. Smith, R. Motekaitis, NIST Critically Selected Stability Constants of Metal Complexes Database v. 8.0 2004 (National Institute of Science and Technology: Gaithersburg, MD). Available at http://www.nist.gov/srd/nist46.cfm [Verified 28 February 2013].

[30]  W. Stumm, J. J.Morgan, Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters, 3rd edn 1996 (Wiley: New York).

[31]  J. L. Beckers, P. Bocek, Peaks in capillary zone electrophoresis: fact or fiction. Electrophoresis 1999, 20, 518.
Peaks in capillary zone electrophoresis: fact or fiction.CrossRef | 1:CAS:528:DyaK1MXis1WjtLY%3D&md5=379b685f854d0a0007c3b44e806228b9CAS | open url image1

[32]  B. Gaš, E. Kenndler, System zones in capillary zone electrophoresis. Electrophoresis 2004, 25, 3901.
System zones in capillary zone electrophoresis.CrossRef | 15597426PubMed | open url image1

[33]  E. E. Martsinko, I. I. Seifullina, T. G. Verbetskaya, Heteronuclear complexes of germanium(IV) and of some other 3D metals with diethylenetriaminepentaacetic acid. Russ. J. Coord. Chem. 2005, 31, 541.
Heteronuclear complexes of germanium(IV) and of some other 3D metals with diethylenetriaminepentaacetic acid.CrossRef | 1:CAS:528:DC%2BD2MXosVagsr4%3D&md5=5ddcb6417980c650729a6988daa2833cCAS | open url image1

[34]  A. Jouyban, E. Kenndler, Theoretical and empirical approaches to express the mobility of small ions in capillary electrophoresis. Electrophoresis 2006, 27, 992.
Theoretical and empirical approaches to express the mobility of small ions in capillary electrophoresis.CrossRef | 1:CAS:528:DC%2BD28Xjt1Sgu7k%3D&md5=e8f8a7846995f9e7a4cfd8b555682c39CAS | 16470782PubMed | open url image1

[35]  D. Li, C. A. Lucy, Prediction of electrophoretic mobilities. 4. Multiply charged aromatic carboxylates in capillary zone electrophoresis. Anal. Chem. 2001, 73, 1324.
Prediction of electrophoretic mobilities. 4. Multiply charged aromatic carboxylates in capillary zone electrophoresis.CrossRef | 1:CAS:528:DC%2BD3MXhtFyntr4%3D&md5=1898d2fc72ace5d115025085f8370b9eCAS | 11305670PubMed | open url image1

[36]  J. E. Sonke, V. J. M. Salters, Disequilibrium effects in metal speciation by capillary electrophoresis inductively coupled plasma mass spectrometry (CE-ICP-MS); theory, simulations and experiments. Analyst 2004, 129, 731.
Disequilibrium effects in metal speciation by capillary electrophoresis inductively coupled plasma mass spectrometry (CE-ICP-MS); theory, simulations and experiments.CrossRef | 1:CAS:528:DC%2BD2cXmtFOisrg%3D&md5=96d844cf03b34e19b339a6d15a22bca8CAS | 15284917PubMed | open url image1

[37]  J. L. Beckers, P. Bocek, The preparation of background electrolytes in capillary zone electrophoresis: golden rules and pitfalls. Electrophoresis 2003, 24, 518.
The preparation of background electrolytes in capillary zone electrophoresis: golden rules and pitfalls.CrossRef | 1:CAS:528:DC%2BD3sXhtlCntr8%3D&md5=e115b86aa7463032ee03f4ba54bb3768CAS | 12569542PubMed | open url image1

[38]  B. Jeżowska-Trzebiatowska, L. Latos-Grazyński, H. Kozlowski, PMR studies of nickel(II)–DTPA complexes aqueous solutions. Inorg. Chim. Acta 1977, 21, 145.
PMR studies of nickel(II)–DTPA complexes aqueous solutions.CrossRef | open url image1

[39]  R. E. Sievers, J. C. Bailar, Some metal chelates of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid. Inorg. Chem. 1962, 1, 174.
Some metal chelates of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid.CrossRef | 1:CAS:528:DyaF38XktV2hs7o%3D&md5=9d9be677e8e572d3c4ebe4a18b65e912CAS | open url image1

[40]  S. Chaberek, A. E. Frost, M. A. Doran, N. J. Bicknell, Interaction of some divalent metal ions with diethylenetriaminepentaacetic acid. J. Inorg. Nucl. Chem. 1959, 11, 184.
Interaction of some divalent metal ions with diethylenetriaminepentaacetic acid.CrossRef | 1:CAS:528:DyaF3cXitFOnsQ%3D%3D&md5=63af2e8904c3943b1417c5d71c6e6697CAS | open url image1



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