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Ionic liquids in analytical chemistry and their applications in mass spectrometry

Ionic liquids in analytical chemistry and their applications in mass spectrometry. 13 September 2006 Farzad Fani Pakdel. What are ionic liquids?. Ionic liquids (ILs) are pure organic salts that have a melting point below 100 ° C. Some are liquid at room temperature (RTIL)

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Ionic liquids in analytical chemistry and their applications in mass spectrometry

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  1. Ionic liquids in analytical chemistry and their applications in mass spectrometry 13 September 2006 Farzad Fani Pakdel

  2. What are ionic liquids? • Ionic liquids (ILs) are pure organic salts that • have a melting point below 100°C. • Some are liquid at room temperature (RTIL) • The cation usually contains nitrogen • with 4 covalent bonds -AgX G. A. Baker et al. Analyst, 2005, 130, 800–808 http://www.rsc.org/chemistryworld/Issues/2004/April/saccharine.asp

  3. Properties of ionic liquids • Low vapor pressure • High viscosity • Good solvents for both organic and inorganic compounds • Broad liquid range • High conductivity • Wide electrochemical window (4.5 - 6 v) • Thermal and oxidative stability • Nonflammability http://www.le.ac.uk/ch/staff/apa1_resint.html

  4. History 1914: knowledge of liquid alkylammonium nitrates [EtNH3+][NO3-] mp = 12°C 1970s: Haloaluminate RTILs were used as electrolyte instead of molten salts in thermal batteries 1992: Synthesis of new ILs with PF6 –and BF4 – anions and following that: Air and moisture stable ionic liquids widely used in synthetic chemistry as solvents Analytical chemists have started taking advantage of their properties Ionic liquid related Publications vs. year G. A. Baker et al. Analyst, 2005, 130, 800–808

  5. Out line • Ionic liquids in analytical chemistry: • Mass spectrometry: • MALDI (Matrix assisted laser desorption ionization) • Matrix properties in MALDI-MS • Ionic liquids as matrices • Quantitative and reproducible • Electrospray • Chromatography • Extraction • Electrochemistry • Electrophoresis • Spectroscopy

  6. How does MALDI work? http://www.chm.bris.ac.uk/ms/theory/maldi-ionisation.html

  7. Effective MALDI matrix • Cocrystallize with sample (solid matrix) • Dissolve the sample (liquid matrix) • Strong absorption of laser light (e > 10 000) • Vacuum stable • Promote the ionization of the sample • Form a homogenous solution with analyte • (shot to shot reproducibility)

  8. Solid matrices • Cocrystallize with analyte • Strong absorption of laser light • Vacuum stable • Promote the ionization of the sample • Form a homogenous solution with analyte (reproducibility) a-cyano-4-hydroxycinnamic acid (CHCA) sinapinic acid (SA) Hot spot

  9. Liquid matrices Not Vacuum stable: changeable matrix due to volatility evaporation Do not contain the desired UV chromophore: have to add other components Glycerol: vacuum stable metal nano-particles added to glycerol

  10. Ideal matrix A UV absorbing liquid that has a low vapor pressure Dissolves the sample and can promote sample ionization (proton transfer) IONIC LIQUIDS

  11. Ionic Liquids as Matrixes for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Daniel W. Armstrong, Li-Kang Zhang, Lingfeng He and Michael L. Gross* Iowa State University Ames, Iowa Analytical Chemistry. 2001, 73(15), 3679 * Washington University St. Louis, Missouri

  12. Paper summary 36 different ionic liquids and 2 solid matrices were tested as MALDI matrix: 4 different analytes were used to study: (CHCA) sinapinic acid (SA) Human Insulin (5809) and Horse skeletal Apomyoglobin (16953) Bradykinin (1060) arg - pro - pro - gly - phe - ser - pro - phe – arg PEG (2000) Intensity and reproducibility for different matrices were investigated http://www.sickkids.ca/HowellLab/custom/insulin.asp

  13. Experimental Water ( ACN-water for PEG) Acetonitrile/ water (2/1, 0.1% TFA) Analyte matrix 4mL 4mL 1mL air stream SS plate Voyager-RP Biospectrometry time-of-flight mass spectrometer positive-ion mode was used Nitrogen laser (337-nm, 3-ns pulse), with a intensity up to 200 mJ /pulse

  14. 18 ILs with no signal No proton

  15. Sinapinic acid and its organic salts as matrix Matrix is a solid organic acid No Signal IL with signal equal to or higher than organic acid

  16. CHCA and its organic salts Out line 40 000 40 000 24 000 40 000 50 000 57 000 53 000 52 000 56 000 45 000 50 000 55 000 61 000 56 000 50 000 52 000 45 000 64 000 34 000 50 000 62 000

  17. Sample mass spectra Human Insulin (5809) Intensity ( x 104 ) 5000 6000 7000 5000 6000 7000 5000 6000 7000 m/z Horse Apomyoglobin (16953) Intensity ( x 104 ) Solid matrix IL matrix 16000 17000 16000 17000 18000 16000 17000 18000

  18. PEG mass spectra Solid matrix IL matrix

  19. Reproducibility CHCA Ionic liquid

  20. Ionic-Liquid Matrices for Quantitative Analysis by MALDI-TOF Mass Spectrometry Ying L. Li and Michael L. Gross Washington University St. Louis, Missouri J Am Soc Mass Spectrom. 2004, 15, 1833–1837

  21. Calibration curves for the MALDI quantification of Bradykinin Internal standard: substance P

  22. MALDI quantification of bradykinin, melittin and bovine insulin Substance P internal standard

  23. Advantages and disadvantages of ILs in MALDI • Homogenous solutions with different analytes: • Better shot to shot reproducibility • No need for search of hot spot • Many choices of ionic liquids for different analytes • No signal depletion (even after 100 laser shots) • Quantitative analysis also possible (as well as solid matrix) • Not commercially available yet • The relation between signal and IL structure is not well understood • Quantitative analysis for mixtures was not shown

  24. Out line • Ionic liquids in analytical chemistry: • Mass spectrometry: • MALDI (Matrix assisted laser desorption ionization) • Matrix properties in MALDI-MS • Ionic liquids as matrices • Quantitative and reproducible • Electrospray • Chromatography • Extraction • Electrochemistry • Electrophoresis • Spectroscopy

  25. Electrospray ionization in hexane 1st ESI in non-polar solvent Analyte: [HNEt3][HFe3(CO)11] Addition of IL (CA) dissolves the analyte In hexane C6 + C6 C = P C6 C14 _ [N(SO2CF3)2]2 A = M. Henderson, J. McIndoe. Chem. Commun., 2006, 2872–2874

  26. Gas chromatography monomer GC capillary was coated by polymerization of ILS as stationary phase. Column temperature: 100 °C hold 2 min, 15 °C/min to 260 °C. Cross-linker Separation of fatty acid methyl esters (C6-C24) Armstrong, D.W; Anderson, J. Analytical Chemistry, 2005, 77 (19)

  27. Extraction G. A. Baker et al. Analyst, 2005, 130, 800–808

  28. Electrochemistry Electrochemical detection of gases in IL [N6222][Tf2N] Cyclic voltammogram of the O2 / O2 - 5 mm radius gold microdisk electrode, n = 500 mV/ s G. A. Baker et al. Analyst, 2005, 130, 800–808 M. C. Buzzeo, R. G. Evans and R. G. Compton, ChemPhysChem, 2004, 5, 1106–1120.

  29. Electrophoresis Detection of different polyphenols in grape seed extract IL 1-ethyl-3-methylimidazolium Tetrafluoroborate used as running electrolyte A-C: grape seed extract D: polyphenol standards G. A. Baker et al. Analyst, 2005, 130, 800–808

  30. Spectroscopy Fluorescence enhancements in IL Fluorescence spectra of Rhodamine 6G dye in 4 different IL solvents and deionized water (DI) Jared L. Anderson, Daniel W. Armstrong and Guor-Tzo Wei, Analytical Chemistry. 2006, 78(9), 2893-2902

  31. Conclusion • The application of Ionic liquids in analytical chemistry is growing: • Chromatography • MALDI • Electrochemistry • Extraction • New ionic liquids will emerge • Commercial availability of ILs will increase • Possible new applications: • Nano science (charged nano-particles, hydrophobic nano-pores) • Laser Induced Back Ablation • New particles: (drug delivery, liquid aerosol)

  32. Acknowledgments: • Dr. Nicolo Omenetto • Winefordner-Omenetto- Smith group • Dr. David Powell • Dr. Kathryn Williams

  33. THANK YOU!

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