Electrified droplet fission and the Rayleigh limit

Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH -ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors.

Section: Profiling the Plume Phmentioning

confidence: 99%

Basic Vapor Exposure for Tuning the Charge State Distribution of Proteins in Negative Electrospray Ionization: Elucidation of Mechanisms by Fluorescence Spectroscopy

Girod

Antoine

Dugourd

et al. 2012

“…This capability allowed simultaneous levitation with subsequent separation of a population of droplets created from a single starting solution, but the droplets had varied magnitudes of net charge. After the droplets were ejected from the EDB and collected on a glass slide or MALDI plate, the solids contained in the deposited droplets were characterized using microscopy and MALDI-TOF-MS. T he physics of droplets that possess net charge is a subject that continues to receive considerable theoretical and experimental attention 140 years after initial independent studies by Lord Kelvin and Lord Rayleigh [1][2][3][4][5][6][7]. Less well characterized is the condensed phase chemistry that could occur within such droplets as a result of the net charge that is localized in the diffuse layer at the droplet-air interface [8,9].…”

mentioning

confidence: 99%

Promotion of α-cyano-4-hydroxycinnamic acid and peptide cocrystallization within levitated droplets with net charge

Bogan

Bakhoum

Agnes

2005

Many reactions occur as a result of charge imbalance within or between reactive species in reaction vessels that have zero net charge. Here, chemical processes taking place within reaction vessels having net excess charge were studied. For mass spectroscopists, a familiar example of vessels that defy electroneutrality are the charged droplets produced by an electrospray ion source. Evidence is presented that control of the magnitude of the net charge contained in a reaction vessel, in this case a levitated droplet, can be used to promote nucleation and crystal growth of a mixture of an organic acid, ␣-cyano-4-hydroxycinnamic acid (CHCA), with one or more peptides. This phenomenon was first observed during our ongoing development of wall-less sample preparation (WaSP), electrodynamic charged droplet processing methodology capable of creating micrometer-sized sample spots for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) from subnanoliter volumes of sample material. Peptide ion signal-to-noise (S/N) ratios obtained by MALDI-TOF-MS from sample spots created from droplets that had high relative magnitude of net charge were consistently greater than those detected from sample spots created from droplets that had lower net charge. To study this unexpected phenomenon further, WaSP methodology was developed to process different mass-to-charge (m/z) droplets levitated in an electrodynamic balance (EDB), facilitating their deposition onto different positions of a target to create arrays of droplet residues ordered from highest to lowest m/z. This capability allowed simultaneous levitation with subsequent separation of a population of droplets created from a single starting solution, but the droplets had varied magnitudes of net charge. After the droplets were ejected from the EDB and collected on a glass slide or MALDI plate, the solids contained in the deposited droplets were characterized using microscopy and MALDI-TOF-MS. T he physics of droplets that possess net charge is a subject that continues to receive considerable theoretical and experimental attention 140 years after initial independent studies by Lord Kelvin and Lord Rayleigh [1][2][3][4][5][6][7]. Less well characterized is the condensed phase chemistry that could occur within such droplets as a result of the net charge that is localized in the diffuse layer at the droplet-air interface [8,9]. Such chemistry could be rich. For instance, mass spectrometry studies of cluster ions released from charged droplets in an electrospray have identified shifts in chemical equilibria and the formation of preferred nanocrystalline structures [10 -14]. It is possible that these perturbations in the chemical processing are dominated by effects that transpire because the reaction vessels defy electroneutrality.Here we apply electrodynamic levitation technology [15][16][17], microscopy, and MALDI-MS to characterize chemistry that occurred within levitated droplets as a function of the magnitude of their net charge. Droplets were d...

“…However, Figure 1b also revealed that not all the sample material was deposited in this spot, with some of the material spreading as far as 750 m away. The spreading of material observed was due to the evaporating droplets becoming electrostatically unstable during transit through the EDB, causing them to undergo Coulomb fission [22]. In support of these visual observations, the S/N of the lysozyme molecule with a single proton adducted in the mass spectra collected from this spot, denoted by the arrow in Figure 1b, was poor ( Figure 2a).…”

Section: The Role Of a Surface Tension Modifier On Sample Spot Preparmentioning

confidence: 65%

“…The amount of net excess charge a droplet can carry is directly proportional to the square root of its surface tension [22], so an increase in the surface tension will reduce the tendency for a droplet to undergo fission. A new solution was made that contained 0.8% glycerol by volume (Solution Ib, Table 1).…”

Section: The Role Of a Surface Tension Modifier On Sample Spot Preparmentioning

confidence: 99%

Wall-less sample preparation of μm-sized sample spots for femtomole detection limits of proteins from liquid based UV-MALDI matrices

Bogan

Agnes

2004

Previously, we introduced wall-less sample preparation (WaSP), technology that involves the use of an electrodynamic balance (EDB) to prepare m-sized sample spots for analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In that work we demonstrated the detection of femtomole quantities of a low molecular weight peptide and a hydrophobic ester (both Ͻ600 Da). Here we use WaSP to test the hypothesis that the use of small sample spot sizes and an instrument equipped with delayed extraction would increase the analytical utility of liquid sample spots for peptide and protein (Ͼ2500 Da) analysis by UV-MALDI-TOF-MS (Sze et al.; J. Am. Soc. Mass Spectrom. 1998, 9, 166 -174). To aid the optimization of preparing m-sized sample spots by WaSP, optical microscopy and mass spectrometry were used to investigate nonvolatile solute concentration effects on droplet fission and sample spot size, modifications of the EDB electric field to control droplet ejection, and the use of multiple droplet deposition to increase sample loading. Also described is a rapid deposition mode of operation for WaSP that allows single droplets generated at 1 Hz to be levitated briefly (ϳ500 ms) before being ejected autonomously and deposited as a concentrated sample spot with a spatial accuracy of Ϯ5 m. To test the sensitivity of the method, one hundred glycerol droplets (270 pL each, 27 nL total) each containing 32 amol lysozyme were deposited on top of each other one-at-a-time to create a single sample spot. Using a mass spectrometer equipped with delayed extraction to analyze this sample spot, we verified the hypothesis of Sze et al. by achieving detection limits three orders of magnitude below that previously observed for the detection of a protein by UV-MALDI-TOF-MS with a chemical-doped liquid matrix sample preparation. (J Am Soc Mass Spectrom 2004, 15, 486 -495)