Automated deconvolution and deisotoping of electrospray mass spectra

Electrospray ionization (ESI) of peptides and proteins produces a series of multiply charged ions with a mass/charge (m/z) ratio between 500 and 2000. The resulting mass spectra are crowded by these multiple charge values for each molecular mass and an isotopic cluster for each nominal m/z value. Here, we report a new algorithm simultaneously to deconvolute and deisotope ESI mass spectra from complex peptide samples based on their mass-dependent isotopic mean pattern. All signals corresponding to one peptide in the sample were reduced to one singly charged monoisotopic peak, thereby significantly reducing the number of signals, increasing the signal intensity and improving the signal-to-noise ratio. The mass list produced could be used directly for database searching. The developed algorithm also simplified interpretation of fragment ion spectra of multiply charged parent ions.     

The analysis of polystyrene and polystyrene aggregates into the mega dalton mass range by cryodetection MALDI TOF MS

Mass spectra of atactic polystyrene were collected into the mega-dalton mass range with a matrix-assisted laser desorption ionization time of flight (MALDI TOF) mass spectrometer, which incorporates a cryodetector comprised of an array of 16 superconducting tunnel junctions (STJ). The STJ cryodetector, theoretically, has no loss in signal response at any mass compared with the reduced signal found at high mass when using a conventional secondary-ionization detector. Since ion detection at high m/z is one of the fundamental limitations of mass spectrometry (MS), the cryodetector was used to explore the high m/z limit of the MALDI TOF technique for the analysis of two polymer types. Mass spectra were collected for polystyrene at Mn 170, 400, 900, and 2000 kDa and polymethyl methacrylate (PMMA) at Mn 62.6 kDa and 153.7 kDa. For polystyrene, the data showed a trend toward increased aggregation and charge state with mass. The Mn 2 MDa polystyrene data revealed a peak at m/z 2.2 MegaTh and a charge state analysis revealed that these ions were primarily polystyrene aggregates with a mass of approximately 4 MDa. This aggregate assignment was possible because the cryodetector response allows for the determination of a charge state up to about four. The contribution of each charge state for a selected peak can be determined in this fashion. This analysis revealed the preferential formation of doubly charged even-numbered aggregates over odd-numbered aggregates for high molecular mass polystyrene. A potential mechanism for the aggregation process for doubly charged species is discussed.     

Kinetic-energy-sensitive mass spectrometry for separation of different ions with the same m/z value

A double-focusing mass spectrometer (MS) equipped with a superconducting-tunnel-junction (STJ) detector has been applied to measure relative ionization cross-sections for the production of ions that are accompanied by different ion species with the same mass-to-charge (m/z) value. The STJ detector fabricated for this study enables kinetic energy (E) measurement of incoming individual ions at a counting rate of up to approximately 100 k ions/s and an energy resolution (DeltaE/E) of 15%. Both high counting rate and high-energy resolution are necessary to independently determine both m and z and not the m/z value only in ion-counting MS experiments. Ions such as (14)N(2) (2+) and (14)N(+) with the same m/z value can be clearly discriminated using a kinetic-energy-sensitive MS. This fine discrimination capability allows direct determination of relative ionization cross-sections of the homonuclear diatomic ions (14)N(2) (2+)/(14)N(2) (+) and (16)O(2) (2+)/(16)O(2) (+), which are difficult to measure due to the strong interference by the signals of their dissociated atomic ions with noticeably large ionization cross-sections. The new instrument requires no low-abundance heteronuclear diatomic molecules of the forms (14)N(15)N or (16)O(17)O to carry out ionization studies and thus, is expected to be useful in fields such as atmospheric science, interstellar science, or plasma physics.     

Radial stratification of ions as a function of mass to charge ratio in collisional cooling radio frequency multipoles used as ion guides or ion traps

Collisional cooling in radio frequency (RF) ion guides has been used in mass spectrometry as an intermediate step during the transport of ions from high pressure regions of an ion source into high vacuum regions of a mass analyzer. Such collisional cooling devices are also increasingly used as 'linear', two-dimensional (2D) ion traps for ion storage and accumulation to achieve improved sensitivity and dynamic range. We have used the effective potential approach to study m/z dependent distribution of ions in the devices. Relationships obtained for the ideal 2D multipole demonstrate that after cooling the ion cloud forms concentric cylindrical layers, each of them composed of ions having the same m/z ratio; the higher the m/z, the larger is the radial position occupied by the ions. This behavior results from the fact that the effective RF focusing is stronger for ions of lower m/z, pushing these ions closer to the axis. Radial boundaries of the layers are more distinct for multiply charged ions, compared to singly charged ions having the same m/z and charge density. In the case of sufficiently high ion density and low ion kinetic energy, we show that each m/z layer is separated from its nearest neighbor by a radial gap of low ion density. The radial gaps of low ion population between the layers are formed due to the space charge repulsion. Conditions for establishing the m/z stratified structure include sufficiently high charge density and adequate collisional relaxation. These conditions are likely to occur in collisional RF multipoles operated as ion guides or 2D ion traps for external ion accumulation. When linear ion density increases, the maximum ion cloud radius also increases, and outer layers of high m/z ions approach the multipole rods and may be ejected. This 'overfilling' of the multipole capacity results in a strong discrimination against high m/z ions. A relationship is reported for the maximum linear ion density of a multipole that is not overfilled.     

Study of the desorption/ionization mechanism in electrospray droplet impact secondary ion mass spectrometry

Electrospray droplet impact (EDI) secondary ion mass spectrometry (SIMS) is a desorption/ionization technique for mass spectrometry in which highly charged water clusters produced from an atmospheric-pressure electrospray are accelerated in vacuum by several kV and impact on the sample deposited on the metal substrate. The abundances of the secondary ions for C(60) and amino acids are measured as a function of the acceleration voltage of the primary charged water droplets. Two desorption/ionization mechanisms are suggested in the EDI ionization processes: low-energy and high-energy regimes. In the low-energy regime, the excess charges in the primary droplets play a role in the formation of secondary ions. In the high-energy regime, samples are ionized by the supersonic collision of the primary droplets with the sample. The yield of secondary ions increases by about three orders of magnitude with increase in the acceleration voltage of the primary droplets from 1.75 kV to 10 kV.     

Subcellular imaging mass spectrometry of brain tissue

Imaging mass spectrometry provides both chemical information and the spatial distribution of each analyte detected. Here it is demonstrated how imaging mass spectrometry of tissue at subcellular resolution can be achieved by combining the high spatial resolution of secondary ion mass spectrometry (SIMS) with the sample preparation protocols of matrix-assisted laser desorption/ionization (MALDI). Despite mechanistic differences and sampling 10(5) times less material, matrix-enhanced (ME)-SIMS of tissue samples yields similar results to MALDI (up to m/z 2500), in agreement with previous studies on standard compounds. In this regard ME-SIMS represents an attractive alternative to polyatomic primary ions for increasing the molecular ion yield. ME-SIMS of whole organs and thin sections of the cerebral ganglia of Lymnaea stagnalis demonstrate the advantages of ME-SIMS for chemical imaging mass spectrometry. Subcellular distributions of cellular analytes are clearly obtained, and the matrix provides an in situ height map of the tissue, allowing the user to identify rapidly regions prone to topographical artifacts and to deconvolute topographical losses in mass resolution and signal-to-noise ratio.     

Use of monoatomic and polyatomic projectiles for the characterisation of polylactic acid by static secondary ion mass spectrometry

The application of polyatomic primary ions is a strongly developing branch of static secondary ion mass spectrometry (S-SIMS), since these projectiles allow a significant increase in the secondary ion yields to be achieved. However, the different limitations and possibilities of certain polyatomic primary ions for use on specific functional classes of samples are still not completely known. This paper compares the use of monoatomic and polyatomic primary ions in S-SIMS for thin layers of polylactic acid (PLA), obtained by spin-coating solutions on silicon wafers. Bombardment with Ga+, Xe+ and SF5+ primary ions allowed the contribution of the projectile mass and number of atoms in the gain in ion yield and molecular specificity (relative importance of high m/z and low m/z signals) to be assessed. Samples obtained by spin-coating solutions with increasing concentration showed that optimal layer thickness depended on the primary ion used. In comparison with the use of Ga+ projectiles, the yield of structural ions increased by a factor of about 1.5 to 2 and by about 7 to 12 when Xe+ and SF5+ primary ion bombardment were applied, respectively. A detailed fragmentation pattern was elaborated to interpret ion signal intensity changes for different projectiles in terms of energy deposition and collective processes in the subsurface, and the internal energy of radical and even-electron precursor ions.     

Analysis of the stochastic variation in LTQ single scan mass spectra

A better understanding of the scan-to-scan signal intensity variation can lead to more sophisticated algorithms for database searching and de novo peptide sequencing using single scan mass spectra. In this study, we systematically studied the variation in relative intensity of m/z values in the single scan product ion mass spectra (MS2) derived from five representative precursor ions (MS1) collected using an LTQ linear ion trap under constant flow direct infusion conditions with peptide concentrations held constant. We applied a matching algorithm based on a pair hidden Markov model to align the peaks from each scan belonging to the same m/z value prior to assessing the signal intensity variation. The most significant single contributor to scan-to-scan signal intensity variation for high abundance ions was centroider error. Our study also showed that the variation in signal intensity is higher than what would be expected if the ion statistics derived from the dual geometry electron multiplier detector followed a Poisson distribution.     

Miniaturized linear time-of-flight mass spectrometer with pulsed extraction

Improved resolution for a miniaturized instrument is demonstrated at high masses using a pulsed extraction, 3(") linear time-of-flight (TOF) mass analyzer. This illustrates the utility of a small and simple mass spectrometer for biological/medical analyses. Current and future applications suggested by this instrument include rapid mass spectral reading of oligonucleotides that differ in one base (single nucleotide polymorphisms), distinction of biomarker signatures from different species of bacterial spores (biological weapons detection) and point-of-care instruments for proteomics-based diagnostics. We have incorporated a two-stage, pulsed-extraction design that places the focal plane of the ions at the detector channel plate surface. The ions are accelerated to a total energy of 12 keV to enable detection of high-mass proteins in a design that incorporates a floatable flight tube set at the voltage of the front channel plate of the detector. The resultant elimination of post-acceleration at the detector is intended to improve mass resolution by reducing the difference in arrival times between ions and their neutral products. Resolutions of one part in 1200 at m/z 4500 and one part in 600 at m/z 12 000 have been achieved. Proteins with molecular masses up to 66 000 Da, mixtures of oligonucleotides, and biological spores have all been successfully measured, results that increase the potential use of this TOF analyzer.     

The high-mass component (>m/z 10 000) of coal tar pitch by matrix-assisted laser desorption/ionisation mass spectrometry and size-exclusion chromatography

The size-exclusion chromatography (SEC) of acetone-soluble, pyridine-soluble and pyridine-insoluble fractions of a coal tar pitch indicates a bimodal distribution in each fraction. The proportion of high-mass material excluded from the SEC column porosity increases with solvent polarity. The polymer calibration of SEC shows the mass range of the small molecules to be from approximately 100 u to approximately 6000 u, with the mass range of the large excluded molecules above 200 000 u and up to several million u. In contrast, matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) shows a similar low-mass range of ion abundances (< m/z 6000), but with a smaller range of high-mass ion abundances, from approximately m/z 10 000 to 100 000. The large molecules may have three-dimensional structures to allow molecules of relatively low mass to behave as if they are of large size in SEC. Laser desorption mass spectrometry of the acetone- and pyridine-soluble fractions produced molecular ions of polycyclic aromatics that can be related to the known compositions from gas chromatography (GC) mass spectrometry. The experimental conditions used to generate the bimodal distribution by MALDI-MS involve reducing the ion signal intensities to avoid overload of the detector and enable detection of the high-mass ions, by reducing the high-mass detector voltage (i.e. sensitivity) and increasing the laser power.     

用Fourier变换质谱研究苯胺衍生物的自身化学电离

报导了3-苯甲酰氧基苯胺和P-溴代苯胺在FT质谱中的自身化学电离, 采用多共振离子消除技术研究离子-分子反应机理. 着重探讨系列离子m/z 200, 290, 380和470的生成机理.     

Tandem mobility mass spectrometry study of electrosprayed tetraheptyl ammonium bromide clusters

Multiply charged electrospray ions from concentrated solutions of Heptyl4N+Br- (designated A+B- hereafter) in formamide are analyzed mass spectrometrically (MS) following mobility selection in ambient air in a differential mobility analyzer (DMA). Most of the sharp mobility peaks seen are identified as (AB)(n)A+ clusters, with 0 < or = n < ot = 5. One anomalously abundant and mobile ion is identified as NH4+(AB)4. Six ions in the (AB)n(A+)2 series are also identified, completing and correcting earlier mobility data for singly and doubly charged ions up to masses of almost 9000 Da. The more mobile of two broad humps seen in the mobility spectrum includes m/z values approximately from 2500 up to 12,000 Da. It is formed primarily by multiply charged (AB)n(A+)z clusters with multiple ammonium bromide adducts. Because of overlapping of many peaks of different m/z and charge state z, only a few individual species can be identified by MS alone in this highly congested region. However, the spectral simplification brought about by mobility selection upstream of the MS reveals a series of broad modulations in m/z space, with all ions resolved in the second, third, ...sixth modulation being in charge states z = 2, 3, ...6, respectively. Extrapolation of this trend beyond the sixth wave fixes the ion charge state (in some cases up to z = 15) and mass (beyond m = 175,000 u). This wavy structure had been previously observed and explained in terms of ion evaporation kinetics from volatile drops, though without mass identification. All observations indicate that the clusters are formed as charged residues, but their charge state is fixed by the Iribarne-Thomson ion evaporation mechanism. Consequently, the measured curve of cluster diameter versus z yields the two parameters governing ion evaporation kinetics. Clusters with z > 1 and electrical mobility Z > 0.495 cm2/V/s are metastable and evaporate a singly charged cluster, probably (AB)2A+, between the DMA and the MS. Plotting the electrical mobilities Z of the clusters in the form (z/Z)1/2 versus m(1/3) (both proportional to cluster diameter) collapse the data for all cluster sizes and charge states into one single straight line for Z below 0.495 cm2/V/s. This linear relation reveals a uniform apparent cluster density of 0.935 g/cm3 and an effective hard-sphere diameter of the air molecules of 0.44 nm. An anomalous mobility increase is observed at diameters below 3 nm.     

Direct determination of serotonin in gut lavage fluid by liquid chromatographic ion trap tandem mass spectrometry

Direct determination of serotonin (5-HT) in gut lavage fluid from patients examined due to various gastrointestinal complaints has been achieved. The method involves addition of 5-methoxytryptamine (5-CH3O-HT) internal standard, centrifugation, filtration and injection of the sample supernatant in a liquid chromatographic system coupled to an ion trap tandem mass detector. Electro-spray in positive mode was used to isolate and fragment the protonated ions [5-HT+H]+ and [5-CH3O-HT+H]+ signals 177 and 191 m/z, respectively. Quantification was carried out by extracting the ion fragment chromatograms at 160 and 174 m/z for 5-HT and 5-CH3O-HT, respectively. The relationship 5-HT/5-CH3O-HT was modelled by using a simultaneous design in order to estimate the optimal amount of internal standard to be added to the samples prior to quantification.     

ToF-SIMS Analysis of Adsorbed Proteins: Principal Component Analysis of the Primary Ion Species Effect on the Protein Fragmentation Patterns

In time-of-flight secondary ion mass spectrometry (ToF-SIMS), the choice of primary ion used for analysis can influence the resulting mass spectrum. This is because different primary ion types can produce different fragmentation pathways. In this study, analysis of single-component protein monolayers were performed using monatomic, tri-atomic, and polyatomic primary ion sources. Eight primary ions (Cs(+), Au(+), Au(3) (+), Bi(+), Bi(3) (+), Bi(3) (++), C(60) (+)) were used to examine to the low mass (m/z < 200) fragmentation patterns from five different proteins (bovine serum albumin, bovine serum fibrinogen, bovine immunoglobulin G and chicken egg white lysozyme) adsorbed onto mica surfaces. Principal component analysis (PCA) processing of the ToF-SIMS data showed that variation in peak intensity caused by the primary ions was greater than differences in protein composition. The spectra generated by Cs(+), Au(+) and Bi(+) primary ions were similar, but the spectra generated by monatomic, tri-atomic and polyatomic primary ion ions varied significantly. C(60) primary ions increased fragmentation of the adsorbed proteins in the m/z < 200 region, resulting in more intense low m/z peaks. Thus, comparison of data obtained by one primary ion species with that obtained by another primary ion species should be done with caution. However, for the spectra generated using a given primary ion beam, discrimination between the spectra of different proteins followed similar trends. Therefore, a PCA model of proteins created with a given ion source should only be applied to datasets obtained using the same ion source. The type of information obtained from PCA depended on the peak set used. When only amino acid peaks were used, PCA was able to identify the relationship between proteins by their amino acid composition. When all peaks from m/z 12-200 were used, PCA separated proteins based on a ratio of C(4)H(8)N(+) to K(+) peak intensities. This ratio correlated with the thickness of the protein films and Bi(1) (+) primary ions produced the most surface sensitive spectra.     

Ion mobility augments the utility of mass spectrometry in the identification of human hemoglobin variants

The global dispersion of hemoglobin variants through population migration has precipitated a need for their identification. A particularly effective mass spectrometry (MS)-based procedure involves analysis of the intact globin chains in diluted blood to detect the variant through mass anomalies, followed by location of the variant amino acid residue by direct analysis of the enzymatically digested globins. Here we demonstrate the use of ion mobility separation in combination with this MS procedure to reduce mass spectral complexity. In one example, the doubly charged tryptic peptide from a low abundance variant (4%) occurred at the same m/z value as a singly and a doubly charged interfering ion. In another example, the singly charged tryptic peptide from an alpha-chain variant (26%) occurred at the same m/z value as a doubly charged interfering ion. Ion mobility was used to separate the variant ions from the interfering ions, thus allowing the variant peptides to be observed and sequenced by tandem mass spectrometry.     

Improvement of biological time-of-flight-secondary ion mass spectrometry imaging with a bismuth cluster ion source

A new liquid metal ion gun (LMIG) filled with bismuth has been fitted to a time-of-flight-secondary ion mass spectrometer (TOF-SIMS). This source provides beams of Bi(n)q+ clusters with n = 1-7 and q = 1 and 2. The appropriate clusters have much better intensities and efficiencies than the Au3+ gold clusters recently used in TOF-SIMS imaging, and allow better lateral and mass resolution. The different beams delivered by this ion source have been tested for biological imaging of rat brain sections. The results show a great improvement of the imaging capabilities in terms of accessible mass range and useful lateral resolution. Secondary ion yields Y, disappearance cross sections sigma, efficiencies E = Y/sigma , and useful lateral resolutions deltaL have been compared using the different bismuth clusters, directly onto the surface of rat brain sections and for several positive and negative secondary ions with m/z ranging from 23 up to more than 750. The efficiency and the imaging capabilities of the different primary ions are compared by taking into account the primary ion current for reasonable acquisition times. The two best primary ions are Bi3+ and Bi5(2+). The Bi3+ ion beam has a current at least five times larger than Au3+ and therefore is an excellent beam for large-area imaging. Bi5(2+) ions exhibit large secondary ions yields and a reasonable intensity making them suitable for small-area images with an excellent sensitivity and a possible useful lateral resolution <400 nm.     

Adduction of solvent molecules by ions isolated within an ion trap mass spectrometer under atmospheric pressure ionisation conditions

Benzylpyridine and papaverine, an alkyl quinoline, both produce product ions containing an azepinium ring during atmospheric pressure chemical ionisation or electrospray multistage mass spectrometry. By controlling the trapping conditions, an isolated azepinium ion was held within the trap for an extended period of time without excitation. A subsequent analytical scan revealed a mass spectrum containing ions at two mass-to-charge (m/z) ratios, the first at the m/z of the isolated product ion and the second at an m/z ratio corresponding to the adduction of a molecule of solvent. Isolation and resonance excitation of the adduct ion remove the solvent molecule, resulting in recovery of the azepinium ion at the same signal intensity as the adduct ion. Isolating and trapping the ion for a further period allowed the solvent adduct ion to be re-formed. Modulation of the solvent flowing into the source while the ion was trapped allowed variation in the solvent molecule adducted to the trapped ion. The proportion of the ion current due to the adduct ion depends on the nature of the isolated ion, the proton affinity of the solvent and the length of time for which the ion was trapped. Adduct ion formation, deliberately maximised in this study, can occur to a significant extent under standard ion trap operating conditions, reducing the ion current of product ions of interest and, ultimately, the response in tandem mass spectrometric assays.     

Detection of Large Ions in Time-of-Flight Mass Spectrometry: Effects of Ion Mass and Acceleration Voltage on Microchannel Plate Detector Response

In time-of-flight mass spectrometry (TOF-MS), ion detection is typically accomplished by the generation and amplification of secondary electrons produced by ions colliding with a microchannel plate (MCP) detector. Here, the response of an MCP detector as a function of ion mass and acceleration voltage is characterized, for singly charged peptide/protein ions ranging from 1 to 290 kDa in mass, and for acceleration voltages from 5 to 25 kV. A nondestructive inductive charge detector (ICD) employed in parallel with MCP detection provides a reliable reference signal to allow accurate calibration of the MCP response. MCP detection efficiencies were very close to unity for smaller ions at high acceleration voltages (e.g., angiotensin, 1046.5 Da, at 25 kV acceleration voltage), but decreased to ~11% for the largest ions examined (immunoglobulin G (IgG) dimer, 290 kDa) even at the highest acceleration voltage employed (25 kV). The secondary electron yield γ (average number of electrons produced per ion collision) is found to be proportional to mv^3.1 (m: ion mass, v: ion velocity) over the entire mass range examined, and inversely proportional to the square root of m in TOF-MS analysis. The results indicate that although MCP detectors indeed offer superlative performance in the detection of smaller peptide/protein species, their performance does fall off substantially for larger proteins, particularly under conditions of low acceleration voltage.

Structural determination of the novel fragmentation routes of zwitteronic morphine opiate antagonists naloxonazine and naloxone hydrochlorides using electrospray ionization tandem mass spectrometry

Electrospray ionization quadrupole time-of-flight (ESI-QqToF) mass spectra of the zwitteronic salts naloxonazine dihydrochloride 1 and naloxone hydrochloride 2, a common series of morphine opiate receptor antagonists, were recorded using different declustering potentials. The singly charged ion [M+H-2HCl](+) at m/z 651.3170 and the doubly charged ion [M+2H-2HCl](2+) at m/z 326.1700 were noted for naloxonazine dihydrochloride 1; and the singly charged ion [M+H-HCl](+) at m/z 328.1541 was observed for naloxone hydrochloride 2. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments established the fragmentation routes of these compounds. In addition to the characteristic diagnostic product ions obtained, we noticed the formation of a series of radical product ions for the zwitteronic compounds 1 and 2, and also the formation of a distonic ion product formed from the singly charged ion [M+H-HCl](+) of naloxone hydrochloride 2. Confirmation of the various established fragmentation routes was effected by conducting a series of ESI-CID-QqTof-MS/MS product ion scans, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. Deuterium labeling was also performed on the zwitteronic salts 1 and 2, in which the hydrogen atoms of the OH and NH groups were exchanged with deuterium atoms. Low-energy CID-QqTof-MS/MS product ion scans of the singly charged and doubly charged deuteriated molecules confirmed the initial fragmentation patterns proposed for the protonated molecules. Precursor ion scan analyses were also performed with a conventional quadrupole-hexapole-quadrupole tandem mass spectrometer and allowed the confirmation of the genesis of some diagnostic ions.     

Characterization of microchannel plate detector response for the detection of native multiply charged high mass single ions in orthogonal-time-of-flight mass spectrometry using a Timepix detector

Time-of-flight (TOF) systems are one of the most widely used mass analyzers in native mass spectrometry (nMS) for the analysis of non-covalent multiply charged bio-macromolecular assemblies (MMAs). Typically, microchannel plates (MCPs) are employed for high mass native ion detection in TOF MS. MCPs are well known for their reduced detection efficiency when impinged by large slow moving ions. Here, a position- and time-sensitive Timepix (TPX) detector has been added to the back of a dual MCP stack to study the key factors that affect MCP performance for MMA ions generated by nMS. The footprint size of the secondary electron cloud generated by the MCP on the TPX for each individual ion event is analyzed as a measure of MCP performance at each mass-to-charge (m/z) value and resulted in a Poisson distribution. This allowed us to investigate the dependency of ion mass, ion charge, ion velocity, acceleration voltage, and MCP bias voltage on MCP response in the high mass low velocity regime. The study of measurement ranges; ion mass = 195 to 802,000 Da, ion velocity = 8.4 to 67.4 km/s, and ion charge = 1+ to 72+, extended the previously examined mass range and characterized MCP performance for multiply charged species. We derived a MCP performance equation based on two independent ion properties, ion mass and charge, from these results, which enables rapid MCP tuning for single MMA ion detection.