An Orbitrap-based ion analysis procedure determines the direct charge for numerous individual protein ions to generate true mass spectra. This individual ion mass spectrometry (I
MS) method for ...charge detection enables the characterization of highly complicated mixtures of proteoforms and their complexes in both denatured and native modes of operation, revealing information not obtainable by typical measurements of ensembles of ions.
Charge detection mass spectrometry (CDMS) of low-level signals is currently limited to the analysis of individual ions that generate a persistent signal during the entire observation period. Ions ...that disintegrate during the observation period produce reduced frequency domain signal amplitudes, which lead to an underestimation of the ion charge state, and thus the ion mass. The charge assignment can only be corrected through an accurate determination of the time of ion disintegration. The traditional mechanisms for temporal signal analysis have severe limitations for temporal resolution, spectral resolution, and signal-to-noise ratios. Selective Temporal Overview of Resonant Ions (STORI) plots provide a new framework to accurately analyze low-level time domain signals of individual ions. STORI plots allow for complete correction of intermittent signals, the differentiation of single and multiple ions at the same frequency, and the association of signals that spontaneously change frequency.
Charged water droplets generated by electrospray, sonic spray, and a vibrating orifice aerosol generator (VOAG) have been studied by digital macrophotography and image charge detection mass ...spectrometry. Image charge detection mass spectrometry provides information on the droplet size, charge, and velocity after transmission through a capillary interface. The digital images provide the droplet size distribution before they enter the capillary. Droplets with 10−100 μm radii generated by sonic spray and VOAG are reduced to 2−3 μm radii by transmission through the capillary interface. The droplets from sonic spray and VOAG are much more highly charged than expected for random charging, and positive droplets are much more prevalent than negative. For positive mode electrospray, >99% of the detected droplets carry a positive charge, whereas for negative mode electrospray, <30% of the detected droplets carry a negative charge (i.e., >70% carry a positive charge). These observation can all be accounted for by the aerodynamic breakup of the droplets in the capillary interface. This breakup reduces the droplets to a terminal size at which point further breakup does not occur. Charge separation during droplet breakup is responsible for the relatively high charges on the sonic spray and VOAG droplets and for the preference for positively charged droplets. The charge separation can be explained using the bag mechanism for droplet breakup and the electrical bilayer at the surface of water.
Charge Separation from the Bursting of Bubbles on Water Bhattacharyya, Indrani; Maze, Joshua T; Ewing, George E ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
06/2011, Letnik:
115, Številka:
23
Journal Article
Recenzirano
Film droplets formed from the bursting of 2.4 mm diameter bubbles on the surface of pure water are predominantly negatively charged. The charge generated per bubble varies chaotically; a few bubbles ...generate more than −3 × 106 elementary charges (e) but the vast majority generate much less. The average is −5 × 104 e/bubble, and it is not significantly affected by bubbling rate or temperature. The charge diminishes with increasing salt concentration and vanishes for concentrations above 10−3 M. We propose a mechanism consistent with the observed charge separation. The model relies on the assumption that the surface of pure water has a slight excess of hydroxide ions. The charge separation results when water with entrained counterions (H3O+) flows out of the thinning film of the bubble cap, leaving behind the excess OH− on the surface. Addition of salt reduces the Debye length, and the charge separation mechanism becomes less effective as the Debye length becomes small compared with the film thickness. The excess charge near the surface of pure water is very small, around −4 nC/m2.
A novel image charge detection mass spectrometer (CDMS) with improved sensitivity and mass accuracy is described. The improved detector design and method of data analysis allow us to measure a ...reliable mass for a single macroion that is an order of magnitude smaller than previously achieved with CDMS. The apparatus employs an image charge detector array consisting of 22 detectors. The detectors are divided into two groups that can be floated at different potentials. The signals from the detector array are analyzed using a correlation approach to yield the velocities in the two groups of detectors and the charge. These quantities, together with the voltage difference between the two groups of detectors, provide a value for the mass. The mass, m/z, and charge distributions recorded for 300 kDa poly(ethylene oxide) (PEG) are presented. The mass distribution shows a peak at around 300 kDa with a width close to that expected from the polymer size distribution. In addition, there are broad peaks in the mass distribution at around 100 and 500 MDa. The 300 kDa ions have m/z ratios of ∼2 kDa/e, and the 100 and 500 MDa ions have m/z ratios of ∼40 kDa/e. The 100 and 500 MDa ions probably result from PEG aggregates that are either present in solution or the residue of large electrospray droplets.
Negative Droplets from Positive Electrospray Maze, Joshua T; Jones, Thaddeus C; Jarrold, Martin F
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
11/2006, Letnik:
110, Številka:
46
Journal Article
Recenzirano
Image charge detection has been used to measure the charge and velocity of individual electrosprayed water droplets. With a positive bias on the electrospray needle the majority of the droplets are, ...as expected, positively charged. However, a small fraction, surprisingly, carry a negative charge. Plausible explanations for the presence of the negatively charged droplets are discussed. In particular, we consider the possibility of the negatively charged droplets resulting from a bipolar fission process where the incorporation of a small negatively charged droplet between two larger positively charged progeny lowers the energy barrier for symmetric fission.
We describe a new approach to measuring the masses of individual macroions. The method employs a pulsed acceleration tube located between two sensitive image charge detectors. The charge and velocity ...of the macroion are recorded with the first image charge detector. The ion is pulse accelerated through a known voltage drop, and then the charge and velocity are remeasured using the second image charge detector. The mass of the ion is deduced from its charge and its initial and final velocities. The approach has been used to measure masses in the 1010−1014 Da range with z = 103−106 and m/z = 106−109. It should be extendable to masses of <106 Da. We have used the method to determine the size and charge of water droplets transmitted through a capillary interface and an aperture interface. The droplets detected from the aperture interface are ∼1 order of magnitude smaller in mass than those detected from the capillary interface. The droplets from both interfaces have relatively low charges, particularly with the capillary interface where they are only charged to a small fraction of the Rayleigh limit. These results suggest that the aerodynamic breakup of the droplets plays a significant role in the mechanism of electrospray ionization.
Studies with two image charge detectors separated by a drift region show that micron sized water droplets fragment and change their charge while traveling through vacuum.
Water droplets are generated ...by sonic spray, transferred into vacuum through a capillary interface, and then passed through two image charge detectors separated by a drift region. The image charge detectors measure the charge and velocity of each droplet. For around 1% of the droplets, the charge changes significantly between the detectors. In some cases it increases, in others it decreases, and for some droplets the charge changes polarity. We attribute the charge changing behavior to fragmentation caused by freezing. Simulations indicate that the time required for a droplet to cool and freeze in vacuum depends on its size, and that droplets with radii of 1–2
μm have the right size to freeze between the two detectors. These sizes correspond to the smaller end of the distribution present in the experiment. When the charge on a droplet increases or changes polarity, fragmentation must be accompanied by charge separation where fragments carry away opposite charges. In some cases, two fission fragments were observed in the second charge detector. We show examples where the droplet breaks apart to give fragments of the same charge and opposite charges. The fragmentation and charge changing behavior found here is consistent with what has been found in the freezing of larger suspended and supported droplets.
Reactivity of Small Mo x O y - Clusters toward Methane and Ethane Wyrwas, Richard B; Yoder, Bruce L; Maze, Joshua T ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
02/2006, Letnik:
110, Številka:
6
Journal Article
Recenzirano
The reactions of Mo2O y - suboxide clusters with both methane and ethane have been studied with a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory ...calculations. Reactions were carried out under “gentle” and “violent” conditions. For methane, a number of products appeared under the gentler source conditions that were more logically attributed to dissociation of Mo2O y - clusters upon reacting with methane to form MoCH2 -, Mo(O)CH2 -, and HMo(O2)CH3 -. With ethane, products observed under the same gentle conditions were Mo(O)C2H2 -, Mo(O)C2H4 -, Mo(O2)C2H4 -, and Mo(O2)(C2H5)2 -. As expected, more products were observed when the reactions were carried out under violent conditions. The photoelectron spectra obtained for these species were compared to calculated adiabatic and vertical electron affinities and vibrational frequencies, leading to definitive structural assignments for several of the products.
Reactivity of Small MoxOy- Clusters toward Methane and Ethane WYRWAS, Richard B.; YODER, Bruce L.; MAZE, Joshua T. ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
02/2006, Letnik:
110, Številka:
6
Journal Article
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