Analytical methods for studying trace metal speciation in the natural environment

1. As Hg Cr Sn Se Pb Cd Fe Cu Zn Ni Co Al ….. Analytical methods for studying trace metal speciation in the natural environment (Analytiske metoder for speciering av spormetaller i naturen) Date: 8 February 2006 Duration: 45 minutes Target groups: 1st and 2nd year Chemistry students

3. Contents • Chemical speciation and fractionation • Analytical strategies and methodological approaches • In-situ (on-field) speciation analysis in aquatic systems • Conclusions

4. 1. Chemical Speciation and Fractionation

5. Chemical Speciation and Fractionation • Chemical species • Speciation analysis • Speciation of an element • Fractionation - Specific forms of an element Fe(II)/Fe(III); As(III)/As(V) CuCl2/CuCO3; Hg/CH3HgCl - Activity of identifying and measuring species - Distribution amongst chemical species in a system - Analytes classification according to physical or chemical properties Acc. to “Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and methodological approaches” (IUPAC Recommendations, Pure Appl. Chem. 2000)

6. Speciation of Metals • Isotopic composition • Electronic and oxidation state • Inorganic compounds and complexes • Organometalic compounds • Organic and macromolecular complexes

7. Benefits and Fields of Interest

8. What is determining the biogeochemical impact of the metal ions species in aqueous systems? • Concentration • Nature of considered organism • Physico-chemical form: • Particulate ( > 1 µm) • Colloidal (1 nm – 1 µm) • Dissolved (< 1 nm): • Free metal ions • Simple inorganic complexes • Complexes with anthropogenic and natural ligands

9. 2. Analytical Strategies and Methodological Approaches

10. Analytical Strategy – the Main Steps • Formulation of the problem • Sampling and sample preparation • Measurement of the analytical signal • Analytical signal interpretation (quantitative and qualitative) • Critical evaluation of the analytical performances and method validation

11. What is relevant in a metal speciation study? Groups of different species with similar properties Individual species • Formulation of the problem

12. Bio-uptake of Metal Species in Soils • Exchangeable fraction: species most available for bio-uptake (reagent used: acetic acid 0.11 M) • Reducible fraction: potentially available for plants (reagent used: a reducing agent like hydroxylamine chloride) • Oxidizable fraction: potentially available for plants (reagent used: an oxidizing agent like H2O2 and NH4COOCH3) • Rezidual fraction: contains naturally occurring minerals

13. Bio-uptake of Metal Species in Aquatic Systems • Free metal ions – related to biological uptake • Dynamic metal species (free metal ions and small labile complexes) – potentially availably for organisms • The particulate and colloidal species – role in transport and residence time The total extractable metals – the reservoir of metal in the test solution

14. Surface-water sampling sites The Baia Mare Accident !! Higher toxicity due to heavy metals (Cu(II), Zn(II))

15. Metal Species in Aquatic Systems • Free metal ions – related to biological uptake • Dynamic metal species (free metal ions and small labile complexes) – potentially availably for organisms • The particulate and colloidal species – role in transport and residence time The total extractable metals – the reservoir of metal in the test solution

16. Sampling – Sample preparation A major challenge in speciation analysis Sampling Transport Pre-treatment Preservation Contamination Loss of analyte Species transformation 2. Sampling and Sample Preparation

17. What is influencing the species stability? • Chemical factors • Physical factors • Biological factors

18. Treatments for Sample Preservation • Acidification • Low-temperature • Drying • Freezing • Pasteurization • Lyophilization • Adsorption on cartridges or solid-phase micro-columns • Storage in the dark Preservation of Sb samples: - Acidification to prevent hydrolysis - Extraction on solid-phase

19. Pb2+(aq) Pb2+(ads) Artifacts in Sample Speciation 0.2 mM Pb2+, pH 6 Fe(OH)3 Fe2+ O2 PS film coated glass • Precipitation • Sorption onto the container walls Glass cell Adapted from J. P. Pinheiro et al., Anal. Bioanal. Chem., 2004

20. Analytical Methods for Trace Metal Analysis and Speciation Analysis • Measuring techniques • Atomic spectroscopy • Inductively coupled plasma-mass spectroscopy (ICP-MS) • Neutron activation analysis (NAA) • X-ray photoelectron spectroscopy • Electroanalytical methods • Separation/ extraction • Chromatography (GC, LC, HPLC) • Capillary electrophoresis • Ion-chromatography • L-L extraction; • Ion-exchange; co-precipitation…. 3. Measurement of the analytical signal

21. Dimethylarsinic acid (DMA, cacodylic acid) O||H3C-As-CH3|  OH Arsenic acid (As+5) O||HO-As-OH|  OH Arsenious acid (As+3) HO-As-OH|  OH Monomethylarsonic acid (MMA) O||H3C-As-OH|  OH IC-ICP-MS Chromatogram of 50 mg/L Arsenic Species Hyphenated techniques for speciation analysis Separation – Excitation – Detection HPLC – ICP – MS GC – ICP – MS IC – ICP – MS

22. Metals speciation analysis by electroanalytical techniques Potentiometry Voltammetry

23. Ion-selective electrodes Free metal ion activity, aI Bioavailability Speciation • Speciation of Pb(II) and Cd(II) in drinking water • Detection of free Cu(II) in sea water • The uptake of Cd(II) species by plant roots LOD: 10-7 – 10-6 M 10-11 – 10-8 M Acc. E. Bakker, E. Pretsch, Trends Anal. Chem., 2005.

24. Voltammetric cell Potentiostat Current – potential curves i - E Measured signal in SWASV WE RE AE Trace metal speciation analysis by voltammetry Anodic stripping voltammetry (ASV) Adsorptive stripping voltammetry (AdSV) Potentiometric stripping analysis (PSA) Anodic stripping voltammetry (ASV)

25. How is an ASV experiment working ? 3 steps experiment: I. Accumulation/Preconcentration (Mz+ + ze- M0(Hg)) II. Equilibration III. Measurement of the analytical signal (M0(Hg)) Mz+ + ze-)

26. Strengths and advantages of the voltammetric techniques • Accuracy • Sensitivity • Simplicity • Low detection limit (ppm - ppt) • Well-suited for automatic in situ speciation • Allow to determine the complexing properties of model or naturally occurring complexants

27. 5. Critical evaluation of the analytical performances and methods validation • To test accuracy and traceability • Use of CRM (Certified Reference Materials) Example of simple certified reference materials for speciation analysis of arsenium and chromium in water samples

28. Why validation methods are important? In situ detection of O2, Fe(II), Mn(II) in sediments porewaters with unprotected Au/Hg WE (100 μm) Acc. G. W. Luther III et al., Environ. Sci. Technol. 33 (1999) 4352

29. 3. In-situ (on-field) speciation analysis in aquatic systems

30. In-situ voltammetric analyzers ATMA (Automated Trace Metal Analyzer) VIP (Voltammetric In situ Profiler) MPCP (Multi Physical-Chemical Profiler)

31. ATMA • PSA measurements • Electrodes: a mercury film deposited on a glassy carbon rod or a thin gold electrode • Used for measuring As(III); Cr(VI); Cu(II); Hg(II); Se(IV). Automated Trace Metal Analyzer (ATMA) Acc. to Space and Naval Warfare Systems Center, San Diego, USA (2002) Interferences from matrix (organics, solids, other metals) can have a dramatic effect on the accuracy of the instrument Caution in use on unpredictable or unknown effluents

32. In situ trace metal speciation based on bioanalogical sensors VIP (Voltammetric In situ Profiler)MPCP (Multi Physical-Chemical Profiler) Gel protected voltammetric microelectrodes - GIME - Gel Integrated Microelectrode - CGIME - Complexing Gel Integrated Microelectrode - PLM – mTAS - Permeation Liquid Membrane – Total Analytical System

33. Model of metal uptake by a biological cell Bulk solution Diffusive boundary layer Cell wall layer Cell membrane kint, M Cell interior

34. GIME (gel-integrated micro-sensor) Test solution (volume) Agarose gel Ir Si3N4 Hg (5 μm) Silicon

35. CGIME (complexing gel-integrated micro-sensor) Test solution (volume) Agarose gel Resin Ir Si3N4 Hg (5 μm) Silicon

36. From voltammetric sensors to in situ probes

37. VIP – Voltammetric In situ Profiler www.idronaut.it • Based on an array of interconnected GIME sensors covered with a 300 mm thick agarose antifouling gel • Measures the concentration of dynamic fraction of trace metals (Cu(II), Pb(II), Cd(II), Zn(II), Mn(II), Fe(II))

38. Voltammetric in situ profiler (VIP)

39. MPCP MPCP (Multi Physical-Chemical Profiler) a system for in-situ trace metal speciation Acc. to M.-L. Tercier-Waeber/ Marine Chemistry 2005 • Speciation of Cu, Cd, Pb • Pressure • pH • Temperature • O2 • Conductivity • Salinity • Redox potential • Turbidity • Chlorophyll a Environmental monitoring and pollution control Biogeochemical studies

40. Channel 2 Channel 3 Channel 1 CGIME FIA - GIME GIME Total extractable metal concentration Free metal ion Dynamic fraction of trace metals MPCP – 3 channels configuration

41. Speciation analysis of copper with MPCP Acc. to M.-L. Tercier-Waeber/ Marine Chemistry 2005

42. Conclusions- In situ voltammetric speciation analysis have many advantages- It demands improvement of the voltammetric devices

43. 4. Conclusions

44. Interdisciplinarity and Speciation Analysis Environmental Chemistry Analytical Chemistry • Transport processes • Consumptive processes • (chemical reactions and biological uptake) Geochemistry Biology and Biochemistry

45. Summary

46. Suggestions for further reading • R. Cornelis, J. Caruso, H. Crews, K. Heuman (Eds.), Handbook of Elemental Speciation: Techniques and Methodology, Wiley, N. Y., 2005. • J. Buffle, G. Hoarvai (Eds.), In situ Monitoring of Aquatic Systems: Chemical Analysis and Speciation, IUPAC Ser. Anal. Phys. Chem. Environ. Syst., Vol. 6, Wiley, Chichester, UK, 2000. • D. M. Templeton, F. Ariese, R. Cornelis, L-G. Danielsson, H. Muntau, H. P. van Leeuwen, R. Łobiński, “Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and methodological approaches”, Pure Appl. Chem. 72 (2000) 1453-1470. • E. Prichard, G. M. MacKay, J. Points (Eds.), “Trace Analysis: a structured approach to obtaining reliable results”, Royal Society of Chemistry, Cambridge, 1996. • Institute for Reference Materials and Measurements (http://www.irmm.jrc.be/html/homepage.htm) • The European Virtual Institute for Speciation Analysis (EVISA) (http://www.speciation.net/)

47. ‘Many shall pass through and learning shall be increased’ Multi pertransibunt et augebitur scientia The Great Instauration, Francis Bacon