Presentation on theme: "ESI-MS: Electrospray Ionization Mass Spectrometry"— Presentation transcript:
1 ESI-MS: Electrospray Ionization Mass Spectrometry Jason RussellUSD - Chem. 730Dec. 4th, 2006
2 Presentation Overview What is ESI-MS?Features of ESI-MSBrief history of the origins of ESIHow ESI-MS worksTwo theories of gas phase ion formation from liquid dropletsExample Applications
3 What is Electrospray Ionization Mass Spectrometry (ESI-MS)? The technique of electrospray transfers ions present in solution into the gas phaseGas phase ions can then be analyzed in a mass specThe mechanism(s) of ionization will be addressed later
4 Features of ESI-MSCan produce multiply charged molecules, decreasing m/z allowing the mass determination of up to 10^7 g/molConsidered a “soft” ionization methodCan preserve solution phase noncovalent interactions in the gas phaseCan study 3-D molecular conformationsCan obtain the molecular massConditions can be adjusted to promote fragmentation usable for molecule identification (usually by using a triple-quad MS)
5 Feature of ESI-MS (cont.) Samples are introduced in solution and at atmospheric pressureCan be interfaced with solution-based separation methodsHPLC/UPLCCETwo basic modes of operationPositive mode – usually for basic moleculesNegative mode – usually for acidic molecules
6 Origins of ESI Electrospray – well known phenomenon since the 1800’s John Zeleney (Univ. Minnesota, Yale)Early 1900’s: Able to see that that charged droplets broke apart after the solvent had evaporatedConfirmed the prediction made by Rayleigh in the 1800’s, known as the Rayleigh limitCoulombic repulsion at a droplet surface would reach a critical value overcoming the surface tensionResult was smaller daughter droplets
7 Origins of ESI (cont.) Malcolm Dole (Northwestern, Baylor) Pioneered the work that laid the foundation for what is now known as ESI-MSTheorized that continued Rayleigh Limit occurrences in charged droplets containing multiple molecules would eventually yield a droplet containing a single charged moleculeResult was a gas phase ionized molecule1968, paper describing the ESI technique using polystyrene and a magnetic sector MSDeveloped the charge residue model (CRM)
8 Origins of ESI (cont.) John Fenn et. al., Built upon the work of Dole Countercurrent desolvating gasExperimented with smaller molecules and used a quadrupole MSSuccessfully mated ESI-MS with LC
9 How ESI-MS WorksThere have been several modifications from the original design of Fenn et. al., but the general concept remains the same
10 J. Fenn. J. Biomolecular Techniques. 13, 101-118(2002). Diagram of a Second-generation ESI-MS Apparatus from Fenn’s Lab (Late 1980’s)J. Fenn. J. Biomolecular Techniques. 13, (2002).
11 N. Cech & B. Enke. Mass Spec. Rev. 20,6, 362-387(2001).
13 Droplet fission may occur with the ejection of up to 20 or more daughter droplets Radius = 1/10 of parent dropletCan be observed with when r > 1umDaughter droplets can be produced with r = 10 nm in usDaughter droplets carry away 2% of the parent mass, but 15% of the chargeR. Cole. “Electrospray Ionization Mass Spectrometry: Fundamentals, Instrumentation, and Applications”. John Wiley and Sons, Inc
15 Close-up of Droplet Formation at the Needle Tip
16 Electrospray Process Viewed Through a High Resolution Microscope With Increasing Voltages at the Needle Tip
17 Theories of Ion Transfer to the Gas Phase Charge Residue Model (M. Dole)Ion Evaporation Model (Iribarne and Thomson)With very small radii (< 1nm), the two processes are currently indistinguishableThe IEM model is viewed as the most likely mechanism, although there is experimental evidence to support both
19 Very Large Mw Molecules J. Fenn & T. Nohmi. J. Am. Chem. Soc. 114, (1992)
20 N. Cech & B. Enke. Mass Spec. Rev. 20,6, 362-387(2001). Proteins (Myglobin)N. Cech & B. Enke. Mass Spec. Rev. 20,6, (2001).
21 Multiple Charging and Deconvolution – Bovine Serum Albumin R. BakhTiar & F. Tse. Mutagenesis. 15(5), (2000).
22 Estimation of protein surface areas in Solution Determination of dissociation constants for protein-ligand complexesRelating polarity character of peptides and small proteins by their ESI responseAmino acid analysis
23 CE-ESI-MS Amino Acid Determination T. Soga & D. Heiger. Anal. Chem. 72, (2000)
24 Monitoring Electrochemical Reactions G. Van Berkel & K. Asano. Anal. Chem. 76, (2004)
25 G. Van Berkel & K. Asano. Anal. Chem. 76, 1493-1499(2004)