Soft Ionization Methods Research Articles

Sample preparation and fractionation techniques for intact proteins for mass spectrometric analysis.

The analysis of proteins in biological samples is highly desirable, given their connection to myriad biological functions and disease states, as well as the growing interest in the development of protein-based pharmaceuticals. The introduction and maturation of "soft" ionization methods, such as electrospray ionization and matrix-assisted laser desorption/ionization, have made mass spectrometry an indispensable tool for the analysis of proteins. Despite the availability of powerful instrumentation, sample preparation and fractionation remain among the most challenging aspects of protein analysis. This review summarizes these challenges and provides an overview of the state-of-the-art in sample preparation and fractionation of proteins for mass spectrometric analysis, with an emphasis on those used for top-down proteomic approaches. Biological fluids, particularly important for clinical and pharmaceutical applications and their characteristics are also discussed. While immunoaffinity-based methods are addressed, more attention is given to non-immunoaffinity-based methods, such as precipitation, coacervation, size exclusion, dialysis, solid-phase extraction, and electrophoresis. These techniques are presented in the context of a significant number of studies where they have been developed and utilized.

A comparison of electron ionization mass spectra obtained at 70 eV, low electron energies, and with cold EI and their NIST library identification probabilities

Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70-eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real-world applications. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the "Extractor" exhibits relatively abundant molecular ions compared with the "Inert" ion source, while the "High efficiency source" (HES) provides mass spectra with depleted molecular ions compared with the "Inert" ion source or NIST library mass spectra. These conclusions are demonstrated and supported by experimental data in nine figures and two tables.

Transformation of short-chain chlorinated paraffins by the bacterial haloalkane dehalogenase LinB – Formation of mono- and di-hydroxylated metabolites

Short-chain chlorinated paraffins (SCCPs) are listed as persistent organic pollutants (POPs) under the Stockholm Convention. Such substances are toxic, bioaccumulating, transported over long distances and degrade slowly in the environment. Certain bacterial strains of the Sphingomonadacea family are able to degrade POPs, such as hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). The haloalkane dehalogenase LinB, expressed in certain Sphingomonadacea, is able to catalyze the transformation of haloalkanes to hydroxylated compounds. Therefore, LinB is a promising candidate for conversion of SCCPs. Hence, a mixture of chlorinated tridecanes was exposed in vitro to LinB, which was obtained through heterologous expression in Escherichia coli. Liquid chromatography mass spectrometry (LC-MS) was used to analyze chlorinated tridecanes and their transformation products. A chloride-enhanced soft ionization method, which favors the formation of chloride adducts [M+Cl]- without fragmentation, was applied. Mathematical deconvolution was used to distinguish interfering mass spectra of paraffinic, mono-olefinic and di-olefinic compounds. Several mono- and di-hydroxylated products including paraffinic, mono-olefinic and di-olefinic compounds were found after LinB exposure. Mono- (rt = 5.9–6.9 min) and di-hydroxylated (rt = 3.2–4.5 min) compounds were separated from starting material (rt = 7.7–8.5 min) by reversed phase LC. Chlorination degrees of chlorinated tridecanes increased during LinB-exposure from nCl = 8.80 to 9.07, indicating a preferential transformation of lower chlorinated (Cl<9) tridecanes. Thus, LinB indeed catalyzed a dehalohydroxylation of chlorinated tridecanes, tridecenes and tridecadienes. The observed hydroxylated compounds are relevant CP transformation products whose environmental and toxicological effects should be further investigated.

Understanding Gas Phase Ion Chemistry Is the Key to Reliable Selected Ion Flow Tube-Mass Spectrometry Analyses.

Ion-molecule reactions (IMR) are at the very core of trace gas analyses in modern chemical ionization (CI) mass spectrometer instruments, which are increasingly being used in diverse areas of research and industry. The focus of this Perspective is on the ion chemistry that underpins gas-phase analytical CI methods. Special attention is given to the soft chemical ionization method known as selected ion flow tube-mass spectrometry (SIFT-MS). The processes involved in the ion chemistry of the reagent cations, H3O+, NO+, and O2+•, and the anions, O-•, O2-•, OH-, and NO2-, are discussed in some detail. Stressed throughout is that an understanding of these processes is mandatory to obtain reliable analyses of humid gaseous media such as ambient air and exhaled breath. It is indicated that further research is needed to understand the consequences of replacing helium in some situations by the more readily available nitrogen as the carrier gas in SIFT-MS.

Fluorescence quantum yields of matrices used in ultraviolet matrix‐assisted laser desorption/ionization

Ultraviolet matrix-assisted laser desorption/ionization (MALDI) is among the most popular soft ionization methods in mass spectrometry. Several theoretical models have been proposed to explain the primary ion generation in MALDI. These models require knowledge of various matrix molecular parameters for simulation. One such parameter is the fluorescence quantum yield. However, the fluorescence quantum yield reported in previous studies remains controversial. In this study, we used a commercial and a homemade integrating sphere to measure the absorption and fluorescence quantum yields of several commonly used matrices, including 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid (2,4-DHB), 2,5-dihydroxybenzoic acid (2,5-DHB), 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,4,6-trihydroxyacetophenone, and ferulic acid. The fluorescence quantum yields of these matrices were determined to be low (<0.08) at low laser fluences and decreased as the laser fluence increased. The fluorescence quantum yields at the typical laser fluence for MALDI are below 0.04 (2,4-DHB and 2,5-DHB) and 0.01 (the other matrices). Shot-to-shot fluctuations of fluorescence intensity and absorption are not directly related to the fluctuation of ions. Possible mechanisms for the decrease in the fluorescence quantum yield as the laser fluence increased were discussed. The fluorescence quantum yields of these commonly used matrices are much lower than those reported in previous studies. Although fluorescence quantum yield is an important parameter and it is crucial to obtain an accurate value for theoretical models in simulations, the use of fluorescence quantum yield alone is not a sufficient parameter to justify these models.

GC-MS with photoionization of cold molecules in supersonic molecular beams-Approaching the softest ionization method.

A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic molecular beams (named Cold PI). The system was based on a GC-MS with supersonic molecular beams and its fly-through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only molecular ions with rather uniform response whereas alcohols gave some molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged mass spectrum of molecular ions only could serve for the characterization of fuels.

Application of Copper Salts To Initiate Cluster Formation of Organic Compounds by “Soft” Ionization Methods

This work is aimed at obtaining mixed cluster ions of amino acids with copper salts using soft ionization methods. We have shown that amino acid molecules are capable of forming aggregates stabilized by d-metals. In particular, such clusters can form in the presence of silver salts. In the present work, it is revealed that the largest cluster ions can be obtained using the electrospray ionization method. It is found that, upon ionization of amino acids (leucine, alanine, proline, tyrosine, and tryptophan) in the presence of copper salts, cluster associates with a mass of up to 1500 Da are formed. It is also found that the formation of cluster ions strongly depends on the nature of the amino acid and polarity of the charge in the cluster.

Extraction of monomer-cluster association rate constants from water nucleation data measured at extreme supersaturations

We utilize recently reported data for water nucleation in the uniform postnozzle flow of pulsed Laval expansions to derive water monomer association rates with clusters. The nucleation experiments are carried out at flow temperatures of 87.0 K and 47.5 K and supersaturations of lnS ∼ 41 and 104, respectively. The cluster size distributions are measured at different nucleation times by mass spectrometry coupled with soft single-photon ionization at 13.8 eV. The soft ionization method ensures that the original cluster size distributions are largely preserved upon ionization. We compare our experimental data with predictions by a kinetic model using rate coefficients from a previous ab initio calculation with a master equation approach. The prediction and our experimental data differ, in particular, at the temperature of 87.0 K. Assuming cluster evaporation to be negligible, we derive association rate coefficients between monomer and clusters purely based on our experimental data. The derived dimerization rate lies 2-3 orders of magnitude below the gas kinetic collision limit and agrees with the aforementioned ab initio calculation. Other than the dimerization rate, however, the derived rate coefficients between monomer and cluster j (j ≥ 3) are on the same order of magnitude as the kinetic collision limit. A kinetic model based on these results confirms that coagulation is indeed negligible in our experiments. We further present a detailed analysis of the uncertainties in our experiments and methodology for rate derivation and specify the dependency of the derived rates on uncertainties in monomer and cluster concentrations.

Biochemistry of the Thrombin-Like TLBpic and Its Purification fromBothrops pictus“Jergon de la Costa” (Reptilia: Viperidae)

The venom of snakes is composed of a heterogeneous mixture of simple and complex substances, with inflammation and hyperalgesia being the first symptom caused by the action ofBothropsvenom, generating processes such as leukocyte infiltration, hemorrhage, and the intravascular formation of thrombi. Within the simple substances, we have free amino acids, peptides, nucleotides, carbohydrates, lipids, and biogenic amines (organic molecules) as well as cations and anions (inorganic constituents). Of the ions, we can highlight calcium, which is an important cofactor of some proteolytic enzymes as well as phospholipases A2. And magnesium and zinc are important cofactors of venom metalloproteases. Complex substances are related to proteins and enzymes. Studies related to the total venom of snake present in several organic substances act as pain mediators and are called biogenic amines, such as bradykinin, histamine, 4-hydroxytryptamine,N-methyl-5-hydroxytryptamine,N′-N′-dimethyl-5-hydroxytryptamine, and serotonin. In the present study, a fraction with serinoprotease and coagulant activity has been purified on fibrinogen, called TLBpic, using a cationic ion exchange chromatographic system coupled to an HPLC system. The main characteristic of our protocol is the speed, and the high recovery of the fraction with optimal terms gave result of evidence in the SDS-PAGE gel. The ESI (electrospray ionisation), corresponding to the electrophoresis of proteins in polyacrylamide gels and to their denaturing solubilization in the presence of the SDS ionic detergent, uniting the proteins, breaking hydrophobic interactions, showing a molecular mass of ∼30 kDa, demonstrating high molecular homogeneity that exists in this family of proteins, is a soft ionization method, in which the samples were ionized by the addition or removal of a proton, with very little extra energy to cause fragmentation of the produced ions. Samples with molecular masses greater than 1200 Da originate multicharged ions (M + nH)n+ in the positive ionization mode; this methodology guarantees that the purified material has a high degree of purity.

Recent advances in mass spectrometry studies of non-covalent complexes of macrocycles - A review

Non-covalent molecular interactions are crucial for the formation of supramolecular systems whose applications in the transport and release of drugs, the development of nanoreactors or the design of molecular sensors, among others, make them very hot topic of investigation. The use of mass spectrometry (MS) and soft ionization methods as electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) has allowed the characterization of supramolecular systems. This comprises the characterization of non-covalent complexes formed by synthetic molecules and biomolecules and the study of these host-guest systems with different molecular interactions and thermodynamic aspects. Mass spectrometry is capable of answering many questions regarding analytical characterization of these systems including composition, stoichiometry, and structural aspects as e.g., connectivities and building blocks in the supramolecular complex. These soft ionization techniques together with MS have become the technique of choice for characterizing molecular interactions allowing the design of new molecules capable of self-assembly in supramolecular systems. In this review, the synthetic macromolecules cucurbiturils, calixarenes, crown ethers, catenanes, rotaxanes and cyclodextrins are reviewed due to the wide range of non-covalent interactions that they are able to form in their supramolecular assemblies. Both the non-covalent interactions and the supramolecular structures of these synthetic molecules have been studied by mass spectrometry to characterize their structures, thus showing the power of the technique as a tool for supramolecular analysis.

A Comparative Study for Sonic Spray and Electrospray Ionization Methods to Determine Noncovalent Protein–Ligand Interactions

A comparative study between sonic spray ionization (SSI) and electrospray ionization (ESI) is reported for cluster formation of proteins and ligands. For the observation of cluster formation, the interactions were not classified as specific or nonspecific and the instrumental parameters were held constant for both ion sources. Although ESI is a soft ionization method, it induces the formation of additional cluster formation between the protein–ligand couples. To understand this phenomenon, similar experiments were conducted using the same conditions by SSI. The equilibrium constants (Kd) of these complexes were calculated from the measurements obtained using both SSI and ESI. It is a common belief that SSI follows the charge residue model (CRM) and should form higher numbers of clusters. In the selected cases, although CRM is mostly followed, it does not give the same results in some specific situations. ESI produces more clusters during the ionization process for cytochrome-c maltoheptaose. The dependences of concentration, voltage and pH upon the complex formation were determined and number of maltoheptaose molecules bound were compared for both SSI and ESI sources. The main reason for the higher cluster formation is the applied voltage to the ESI source. High or low voltage causes distortion of globular structure of the proteins that leads to the formation of more clusters in the ESI source.

Structural Analysis of Polyurethane Monomers by Pyrolysis GC TOFMS via Dopant-Assisted Atmospheric Pressure Chemical Ionization.

Polyurethane is one of the most widely used copolymers and is formed by the cross-linking of isocyanates and polyols. Its physical properties have a strong dependence on the monomer structures, making it very important to characterize the monomers in polyurethane. In this study, we developed a method to analyze unknown polyurethane samples using pyrolysis gas chromatography time-of-flight mass spectrometry (Py-GC-TOFMS) with dopant-assisted atmospheric pressure chemical ionization (dAPCI). A set of standard polyurethane foams produced with several different monomers are analyzed by Py-GC-TOFMS. GC-dAPCI-TOFMS is a high-resolution, soft ionization method for GC-MS analysis that provides accurate mass information of GC separated molecules. The data obtained by this approach could effectively classify different monomers using principal component analysis (PCA), grouping polymers with the same monomers, and providing structural features significant to each monomer. Furthermore, characteristic compounds are identified using in-source collision-induced dissociation (CID) and CSI:FingerID analysis. In contrast, the same set of samples analyzed by Py-GC-electron ionization (EI)-MS could only partially separate some of the monomers. Graphical Abstract .

In Situ Liquid Secondary Ion Mass Spectrometry: A Surprisingly Soft Ionization Process for Investigation of Halide Ion Hydration.

The understanding of ion solvation phenomena is of significance due to their influences on many important chemical, biological, and environmental processes. Mass spectrometry (MS)-based methods have been used to investigate this topic with molecular insights. As ion-solvent interactions are weak, ionization processes should be as soft as possible in order to retain solvation structures. An in situ liquid secondary ion MS (SIMS) approach developed in our group has been recently utilized in investigations of Li ion solvation in nonaqueous solution, and it detected a series of solvated Li ions. As traditionally SIMS has long been recognized as a hard ionization process with strong damage occurring at the sputtering interface, it is very interesting to study further how soft in situ liquid SIMS can be. In this work, we used halide ion hydration as an example to compare the ionization performance of the in situ liquid SIMS approach with regular electrospray ionization MS (ESI-MS). Results show that, although ESI has been recognized as a soft ionization method, nearly no solvated halide ions were detected by ESI-MS analysis, which acquired only strong signals of salt ion clusters. In contrast, in liquid SIMS spectra, a series of obvious hydrated halide ion compositions could be observed. We further evaluated the hydration numbers of halide ions and revealed the effects of the ion size, charge density, and polarizability on the hydration phenomenon. Our findings demonstrated that the in situ liquid SIMS approach is surprisingly soft, and it is expected to have very broad applications on investigation of various ion-solvent interactions and many other interesting chemical processes (e.g., the initial nucleation of nanoparticle formation) in liquid environment.

Multi-capillary column high-pressure photoionization time-of-flight mass spectrometry and its application for online rapid analysis of flavor compounds

High-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) is a versatile and highly sensitive analytical technique for online and real-time analysis of trace volatile organic compounds in complex mixtures. However, discrimination of isomers is usually a great challenge for the soft ionization method, and matrix effect is also inevitable under high pressure in the HPPI source. In this work, we describe a first attempt to develop a two-dimensional (2D) hyphenated instrument by coupling of a multi-capillary column (MCC) with a HPPI-TOFMS to overcome these problems. The capability of the MCC-HPPI-TOFMS for discrimination of isomeric compounds and elimination of the matrix effect was demonstrated by analyzing flavor mixtures. With the merits of fast separation, soft ionization and high detection sensitivity, satisfactory effects in the 2D analysis were achieved, despite the relatively low chromatographic resolution of MCC. As a result, three isomers, eucalyptol, l-menthone and linalool, in a flavor mixture were successfully categorized within 90 s, and the matrix effect caused by solvent ethanol was significantly eliminated as well. The limits of detection (LODs) down to sub-ppbv level were achieved for the investigated five flavor compounds without any enrichment process, and an excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. The MCC-HPPI-TOFMS system was preliminarily applied for rapid and online analysis of flavor compounds in the exhaled gas of a volunteer after mouth rinsing with a gargle product. The rapid changes of the three flavor compounds, as well as the steady endogenous metabolite acetone, in the exhaled gas were successfully determined with a time-resolution of only 1.5 min.

Biotransformation of short-chain chlorinated paraffins (SCCPs) with LinA2: A HCH and HBCD converting bacterial dehydrohalogenase

Short-chain chlorinated paraffins (SCCPs) are polyhalogenated hydrocarbons as are hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). They all have been classified as persistent organic pollutants (POPs) under the UN Stockholm Convention. Per se such compounds are transformed slowly in the environment, transported over long distances and accumulate in biota. Several Sphingomonadacea strains isolated from HCH dump sites have evolved to express enzymes that can transform HCHs and HBCDs. We hypothesized that LinA2, a dehydrohalogenase expressed in such bacteria, may also transform CPs to chlorinated olefins (COs). Three mixtures of penta- to deca-chlorinated undecanes (C11), dodecanes (C12) and tridecanes (C13) were exposed to LinA2. High-resolution full-scan mass spectra (R∼8′000) of CPs and COs were obtained applying a soft ionization method, enhancing chloride-adduct [M+Cl]- formation. A mathematical deconvolution procedure was used to separate interfering spectra to verify that LinA2 indeed catalyzed the conversion of CPs to COs. About 20–40% of the material was transformed in 24 h, about 50–70% was converted in 200 h. A bimodal first-order kinetic model could describe transformations of reactive and persistent CPs. Under the given conditions reactive CPs (τ1/2 = 1.4–6.9 h) were converted 30 to 190-times faster than the persistent ones (τ1/2 = 150–260 h). Proportions of persistent isomers (pp) varied from 60 to 80%. Lower chlorinated homologues contained higher proportions of persistent isomers. In conclusion, SCCP mixtures contain both, material that is readily converted by LinA2, and persistent material that is not or only slowly transformed.

Mass spectrometry strategies to unveil modified aminophospholipids of biological interest.

The biological functions of modified aminophospholipids (APL) have become a topic of interest during the last two decades, and distinct roles have been found for these biomolecules in both physiological and pathological contexts. Modifications of APL include oxidation, glycation, and adduction to electrophilic aldehydes, altogether contributing to a high structural variability of modified APL. An outstanding technique used in this challenging field is mass spectrometry (MS). MS has been widely used to unveil modified APL of biological interest, mainly when associated with soft ionization methods (electrospray and matrix-assisted laser desorption ionization) and coupled with separation techniques as liquid chromatography. This review summarizes the biological roles and the chemical mechanisms underlying APL modifications, and comprehensively reviews the current MS-based knowledge that has been gathered until now for their analysis. The interpretation of the MS data obtained by in vitro-identification studies is explained in detail. The perspective of an analytical detection of modified APL in clinical samples is explored, highlighting the fundamental role of MS in unveiling APL modifications and their relevance in pathophysiology.

Gas Chromatography-Tandem Mass Spectrometry of Lignin Pyrolyzates with Dopant-Assisted Atmospheric Pressure Chemical Ionization and Molecular Structure Search with CSI:FingerID.

Dopant-assisted atmospheric pressure chemical ionization (dAPCI) is a soft ionization method rarely used for gas chromatography-mass spectrometry (GC-MS). The current study combines GC-dAPCI with tandem mass spectrometry (MS/MS) for analysis of a complex mixture such as lignin pyrolysis analysis. To identify the structures of volatile lignin pyrolysis products, collision-induced dissociation (CID) MS/MS using a quadrupole time-of-flight mass spectrometer (QTOFMS) and pseudo MS/MS through in-source collision-induced dissociation (ISCID) using a single stage TOFMS are utilized. To overcome the lack of MS/MS database, Compound Structure Identification (CSI):FingerID is used to interpret CID spectra and predict best matched structures from PubChem library. With this approach, a total of 59 compounds were positively identified in comparison to only 22 in NIST database search of GC-EI-MS dataset. This study demonstrates the effectiveness of GC-dAPCI-MS/MS to overcome the limitations of traditional GC-EI-MS analysis when EI-MS database is not sufficient. Graphical Abstract ᅟ.

Mechanistic Understanding Leads to Increased Ionization Efficiency and Selectivity in Dielectric Barrier Discharge Ionization Mass Spectrometry: A Case Study with Perfluorinated Compounds.

Perfluorinated compounds have unique properties and many practical applications, but are difficult to ionize efficiently with soft ionization methods. An active capillary plasma ionization source based on dielectric barrier discharge ionization (DBDI) coupled with mass spectrometry was used to study the ionization pathway of perfluorinated compounds (PFCs), with the aim of both increasing the ionization efficiency and influencing the selectivity for generating product ions in negative ion mode. Cyclic and linear perfluorinated alkanes were found to mainly form [M - F]- and [M - F + O]- ions, respectively; the [M]-• ion was only obtained at low discharge voltage. Additionally, fluorine attachment [M + F]- was observed mostly for perfluorinated alkenes. An isotope labeling experiment with 18O2 showed that the primary source of oxygen in the substitution reaction is molecular oxygen, reacting with the analyte in the form of O-• ions. The abundance of [M - F + O]- ions can thus be enhanced by increasing the plasma voltage to produce a higher O-• ion density. The loss of the fluorine (without substitution by oxygen) was mainly observed at high frequency, a fact which can be exploited for tuning the ionization toward specific product ions. Overall, the mechanistic understanding of the ionization of PFCs allowed to increase the selectivity of the product ions, resulting in increased ionization efficiency.

Ionization Techniques in Mass Spectrometry: A Review

Mass Spectrometry- It is an analytical technique that generates charged particles in the form of ions from the substance to be analysed to measure its mass to charge ratio. Ion Source plays an important role for generation of charged ions which further travels through analyser and ends at detector. The production of intact molecular ions can be achieved under adequate experimental conditions, with minimal fragmentation known as soft ionization method. Neutral species either loss or gain of charge to generates ions. This paper covers an information about various type of mass ion Source (Electron impact, Chemical ionization and field ionization, Desorption-Field desorption, Electro spray ionization, matrix assisted desorption ionization, Plasma desorption) are in use for mass spectroscopy. Ions get affected by change in electrical, magnetic and radiofrequency effect as they containing either positive or negative charges this leads to better resolution of ions.

Charged Bubble Extractive Ionization Mass Spectrometry for Protein Analysis

Abstract Rapid mass spectrometry analysis of protein in liquid sample was carried out by using a charged bubble extractive ionization device. In this work, experimental parameters including gases (N2 and CO2), bubble path length, voltage, and gas pressure on the charged bubble extractive ionization of lysozyme were investigated. Under the optimum experimental parameters including CO2 as extraction gas, bubble path length of 32 cm, solution voltage of 2 kV, and gas pressure of 0.05 MPa, lysozyme in liquid sample were successfully detected with the limits of detection of 1 × 10−8 M in aqueous solution and 1 × 10−7 M in diluted urine (200 times with ultrapure water), respectively. In addition, the limit of detection of 1 × 10−5 M was obtained for undiluted urine sample. By comparing the desalting effects of charged bubble extractive ionization mass spectrometry with ESI-MS, it was found that the charged bubble extractive ionization method could obtain a wider and lower charge state distribution of protein ions, and showed higher tolerance facing non-volatile inorganic salts. Off-line study of the collected catalase after charged bubble extractive ionization showed that 53.9% enzyme activity was remained, which indicated that the proposed method was a soft ionization method. The method had merits including no sample pretreatment, no chemical reagent contamination and high speed, showing potential application to mass spectrometry analysis of protein components in solution samples.