1,721,156 research outputs found
Applications of membrane introduction mass spectrometry to on-line analysis and feedback control of bioreactors, and chemical reactors
No full textInvestigation of the fermentation of glucose with a genetically engineered yeast using membrane introduction mass spectrometry (MIMS) in conjunction with a flow injection analysis (FIA) sampling system is described. The concentration of the major product in the liquid phase, ethanol, is monitored on-line as a function of time using MIMS. FIA is used to inject, in sequence, the sample, the standard, and the flush solution (deionized water). Microfiltered broth plugs are introduced into the mass spectrometer, through a direct insertion membrane probe which uses a hydrophobic silicone membrane. All operations such as sampling, scanning, data acquisition, control of the FIA, calibration, and feedback control are carried out automatically, with the help of a control program written C. The feedback control system described is employed to automate substrate addition. This allows the inhibition of ethanol formation due to high substrate (glucose) concentration to be avoided. Batch and fed-batch fermentations are studied. In a typical fed-batch fermentation the bioreactor is monitored for 50 h. Investigation of the photolysis (254 nm) of aryl esters is undertaken using MIMS. On-line monitoring of the products of photolysis of benzyl acetate in aqueous methanol, and 3,5-dimethoxybenzyl acetate in water, are described. The reaction mixture is exposed to a silicone membrane through which analyte molecules permeate into a triple quadrupole mass spectrometer for qualitative and quantitative analysis. Ions characteristic of the reactant ester and its products are monitored simultaneously and continuously. The results show that the relative photolysis rates are dependent on the solvent and the photon intensity, and the observed products suggest that the photolysis proceeds through both ion and radical pair intermediates. Application of the kinetic method to determine the proton affinity (PA) of peroxyacetyl nitrate (PAN) is illustrated, using MIMS for sample introduction. Proton-bound dimers are generated between PAN, and various reference compounds in a chemical ionization source. The individual mass-selected dimers dissociate upon collision to yield the protonated monomers as the product ions. From their relative ratios the kinetic method provides a value of 795 kJ/mol (190 2.0 kcal/mol) for the PA of PAN
Mass spectrometry: Metamorphosis from an analytical technique to a preparative technology
No full textThe focus of this thesis is the ion/surface collision phenomena at hyperthermal energies, in the range of laboratory energies of 1--100 eV. It particularly emphasizes collisions of large organic ions with organic surfaces at energies corresponding to deposition of ions on surfaces without adverse effects on their structure and/or bioactivity, also known as soft-landing. An overview of the assumptions and prior work in the field of mass spectrometry is used to introduce the reader to the concept of mass spectrometry as an analytical and preparative technique for separation and purification of proteins, with or without charge neutralization upon surface deposition and with preservation bioactivity. Liquid and functionalized surfaces are discussed in the context of finding functionalized surfaces for preservation of bioactivity of soft-landed ions. New capabilities for mass spectrometry are demonstrated by showing that it is possible to soft land proteins and peptides from complex mixtures into glycerol-based liquid surfaces with preservation of bioactivity. It is also shown that appropriate liquid surfaces can be used without any additional treatment to detect the soft-landed material by electrospray ionization (ESI), electrosonic spray ionization (ESSI)[20] or matrix-assisted laser desorption ionization mass spectrometry (MALDI). The liquids can also be further processed to extract the purified protein. Importantly, by adding appropriate enzymes to the liquid surfaces used as soft-landing substrates, the nature of purified proteins can be determined through enzymatic reactions
Application of multistage mass spectrometry to structural analysis and ion-molecule reaction chemistry
No full textGas-phase reaction pathways were elucidated and isomeric ions distinguished using ion-molecule reactions and CAD. These studies were uniquely facilitated when using a pentaquadrupole mass spectrometer, which contains three spatially separate reaction regions, the ion source and two collision/reaction quadrupoles. The ability to mass-analyze ions before and after each collision quadrupole provides a powerful set of MS/MS/MS capabilities. Four isomeric C\sb4\rm H\sb4\sp{+.} ions were found to react with neutral conjugated dienes allene, isoprene, furan, and thiophene by (2+2) and (2+4) cycloaddition and, in several cases, adduct fragments were observed to undergo a second addition of neutral diene. Information on the structure and reaction/fragmentation pathways was obtained using MS/MS/MS sequential product and reaction intermediate scans. The interesting cyclobutadiene radical cation was observed to be the most efficient dienophile. Electrophilic aromatic Cl\sp{+} addition and CO\sp{+\sp\cdot} substitution onto aromatic compounds was studied using NH\sb3\rm{Cl}\sp{+}, Cl-CO\sp+, protonated CH\sb3Cl, and Cl\sp{+} reagent ions. Comparisons of MS\sp3 sequential product spectra of mass-selected product ions with the MS/MS spectra of model ions allowed the determination of the addition sites. These sites were found to have the highest Cl\sp{+} affinities by semi-empirical AM1 molecular orbital calculations. Conditions under which \rm{C\sb2 H\sb4 N\sp{+}}, \rm{C\sb3 H\sb6\ N\sp{+}}, and related nitrilium and immonium ions undergo polar Diels-Alder cycloaddition to the neutral diene isoprene were established. Cycloaddition occurs when the difference in the LUMO(ion) and HOMO(isoprene) energies is small and competing reactions are endothermic. The kinetic method was employed to order the relative gas phase chlorine cation affinities of substituted pyridines by fragmenting Cl\sp{+}-bound dimers of two pyridines. Unlike proton affinities, Cl\sp{+} affinities reveal intramolecular steric effects between ortho groups and the bridge ion which significantly decrease the affinities for the larger Cl\sp{+} ion in the cases of hindered molecules. These steric effects agree well with the corresponding S\sp0 parameters obtained by kinetic measurements in solution. Semi-empirical AM1 molecular orbital calculations were used to place the relative Cl\sp{+} affinities on an absolute scale. Br\sp{+} and I\sp{+} bridge ions were also examined and discussed
Development of multiplexed and miniature mass spectrometers
No full textThe objective of the projects described in the following chapters is the development of new multiplexed and miniature rectilinear ion trap mass spectrometers. The first project, described in chapter 2, is the development of an ESI mass spectrometer coupled with an atmosphere interface and using RIT as the analyzer. The development object is to demonstrate the possibility of using a RIT for the analysis of biological compounds, and furthermore to prove the concept of using RITs in the multiplexed instrument with an atmospheric pressure interface. Design, characterization and applications of a novel multiplexed, four channel mass spectrometer using RIT mass analyzer is described in chapter 3. This instrument is the first example of a fully multiplexed, four channel mass spectrometer with atmospeheric pressure interface with all the four channels operating simultaneously. This instrument increases the versatility of multiplexed instruments by adding the capability of detecting positive as well as negative polarity ions generated by ESI and atmospheric pressure chemical ionization (APCI) sources simultaneouosly. It is desirable to develop techniques to analyze involatile and thermally unstable compounds from large surface area with rapid response time, preferably without special sample preparation. Explosives present special problems for MS due to their great range of volatilities while their occurrence on surfaces makes their direct ionization difficult by traditional methods. The high electron affinities associated with the nitro or nitrate functional groups present in the overwhelming majority of explosives in common use mean that they readily form negative ions by electron capture. Therefore a mass spectrometer capable of detecting the negative ion species feature lower limits of detection and a greater range of analysis than if it were only capable of detecting positively charge explosive ions. Chapter 4 describes development of a miniature mass spectrometer with negative ion detection capability which can analyze explosives directly from surfaces without any specialized sample preparation
Investigation of gas phase ion-molecule reactions and determination of cation affinities using multiple-stage mass spectrometry
No full textGas phase even-cation (4+2\sp+) Diels-Alder reactions, electrophilic aromatic additions, and cation affinities are studied with multiple-stage mass spectrometry in a pentaquadrupole mass spectrometer. The unique capability of the pentaquadrupole mass spectrometer for studying ion/molecule reactions is that it allows reactions to be performed with mass-selected reagent ions as well as allow the mass-selected products of ion/molecule reactions to be structurally characterized. Even cations including acylium ions, nitrilium and immonium ions, protonated and methylated ketone ions, generated by electron impact ionization or chemical ionization, are used in the studies of gas phase Diels-Alder cycloadditions. Tandem and multiple-stage mass spectrometry are used in studying mechanism, regioselectivity, and reactivity-energy gap relationship of the cycloadditions. Evidence for the cycloadditions are also obtained from theoretical calculations. Correlations between the cycloaddition reactivity and the HOMO/LUMO energy gap are observed for the cation systems studied when proton transfer reactions are not favored. Electrophilic brominations are studied in the reactions of BrCO\sp+ and CH\sb3NH\sb2Br\sp+ with gaseous aromatic compounds in the pentaquadrupole mass spectrometer under the nonthermal conditions. The electrophilic bromination proceeds via a -complex to the ring as suggested by sequential product ion spectrum. Linear free energy correlations are observed when the Brown substituent constants \delta\sp+ are plotted against the relative yields of the electrophilic brominations. Reaction constants are found to be 0.23 and 0.56 for BrCO\sp+ and CH\sb3NH\sb2Br\sp+ ions, respectively. The proton affinities of free radicals and the relative cation affinities for pyridines are determined by the kinetic method. The cations studied are Cl\sp+, CN\sp+, OCNCO\sp+, SiCl\sb3\sp+, and SiCl\sp+. Dimers containing these cations are generated via either chemical ionization or ion/molecule reactions. Tandem and multiple-stage mass spectrometry as well as theoretical calculations show these dimers are loosely bound. Interactions between substituent(s) at the ortho-position of substituted pyridines with the cations are studied. Stereoelectronic effects are attributed to the abnormal behavior of the ortho-substituted pyridines
Miniature cylindrical ion traps and arrays
No full textA quadrupole ion trap mass analyzer with simplified geometry, the cylindrical ion trap (CIT), was shown to be well-suited to use in miniature mass spectrometers and even mass spectrometer arrays. Experiments with a single miniature CIT showed acceptable resolution and sensitivity, limited by the ion trapping capacity of the miniature device. Parallel miniature CIT arrays, with each CIT of the same size, were operated with the same rf and ac voltages applied to all of the CITs in the array. In this mode of operation, the array was shown to increase ion trapping capacity and thus sensitivity, compared to a single miniature CIT. Parallel miniature CIT arrays with each CIT of a different size were also examined. In this type of array, each CIT was operated to trap a single mass-to-charge ratio without the need to ramp the rf voltage. A multiple-ion monitoring experiment can be performed in the array, and the rf voltage necessary for operation is simplified and greatly reduced in amplitude. Because of the reduced rf voltage, this type of array is suitable for a fully miniaturized mass spectrometer system that operates under size and power restrictions. Further improvements were also made to improve the resolution of miniature CITs by use of nonlinear resonance ejection, which also facilitated operation with air, instead of helium, as the buffer gas. Non-destructive image current detection in a full sized CIT was also performed. In addition, an improved method of image current detection, differential detection was demonstrated in a hyperbolic ion trap. This new method gives increased signal intensity as well as reduced noise
Reaction Acceleration at Interfaces Studied by Mass Spectrometry
No full textVarious organic reactions, including important synthetic reactions involving C–C, C–N, and C–O bond formation as well as reactions of biomolecules, are known to be accelerated when the reagents are present in confined volumes such as sprayed or levitated microdroplets or thin films. This phenomenon of reaction acceleration and the key role of interfaces played in it are of intrinsic interest and potentially of practical value as a simple, rapid method of performing small-scale synthesis. This dissertation has three focusing subtopics in the field of reaction acceleration: (1) application of reaction acceleration in levitated droplets and mass spectrometry to accelerate the reaction-analysis workflow of forced degradation of pharmaceuticals at small scale; (2) fundamental understanding of mechanisms of accelerated reactions at air/solution interfaces; (3) discovery the use of glass particles as a ‘green’ heterogeneous catalysts in solutions and systematical study of solid(glass)/solution interfacial reaction acceleration as a superbase for synthesis and degradation using high-throughput screening.Reaction acceleration in confined volumes could enhance analytical methods in industrial chemistry. Forced degradation is critical to probe the stabilities and chemical reactivities of therapeutics. Typically performed in bulk followed by LC-MS analysis, this traditional workflow of reaction/analysis sequence usually requires several days to form and measure desirable amount of degradants. I developed a new method to study chemical degradation in a shorter time frame in order to speed up both drug discovery and the drug development process. Using the Leidenfrost effect, I was able to study, over the course of seconds, degradation in levitated microdroplets over a metal dice. This two-minute reaction/analysis workflow allows major degradation pathways of both small molecules and therapeutic peptides to be studied. The reactions studied include deamidation, disulfide bond cleavage, ether cleavage, dehydration, hydrolysis, and oxidation. The method uses microdroplets as nano-reactors and only require a minimal amount of therapeutics per stress condition and the desirable amount of degradant can be readily generated in seconds by adjusting the droplet levitation time, which is highly advantageous both in the discovery and development phase. Built on my research, microdroplets can potentially be applied in therapeutics discovery and development to rapidly screen stability of therapeutics and to screen the effects of excipients in enhancing formulation stabilities.My research also advanced the fundamental understanding of reaction acceleration by disentangles the factors controlling reaction rates in microdroplet reactions using constantvolume levitated droplets and Katritzky transamination as a model. The large surfaceto-volume ratios of these systems results in a major contribution from reactions at the air/solution interface where reaction rates are increased. Systems with higher surface-active reactants are subject to greater acceleration, particularly at lower concentrations and higher surface-to-volume ratios. These results highlight the key role that air/solution air/solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction increased rate constant is at least in part due to limited solvation of reagents at the interface.While reaction acceleration at air/solution interfaces has been well known in microdroplets, reaction acceleration at solid/solution interfaces appears to be a new phenomenon. The Katritzky reaction in bulk solution at room temperature is accelerated significantly by the surface of a glass container compared to a plastic container. Remarkably, the reaction rate is increased by more than two orders of magnitude upon the addition of glass particles with the rate increasing linearly with increasing amounts of glass. A similar phenomenon is observed when glass particles are added to levitated droplets, where large acceleration factors are seen. Evidence shows that glass acts as a ‘green’ heterogeneous catalyst: it participates as a base in the deprotonation step and is recovered unchanged from the reaction mixture.Subsequent to this study, we have systematically explored the solid/solution interfacial acceleration phenomena using our latest generation of a high-throughput screening system which is capable of screening thousands of organic reactions in a single day. Using desorption electrospray ionization mass spectrometry (DESI-MS) for automated analysis, we have found that glass promotes not only organic reactions without organic catalysts but also reactions of biomolecules without enzymes. Such reactions include Knoevenagel condensation, imine formation, elimination of hydrogen halide, ester hydrolysis and/or transesterification of acetylcholine and phospholipids, as well as oxidation of glutathione. Glass has been used as a general ‘green’ and powerful heterogeneous catalyst
Ambient Ionization Mass Spectrometry for High Throughput Bioanalysis
No full textThe rapid analysis of complex samples using mass spectrometry (MS) provides valuable information in both point-of-care (e.g. drug testing) and laboratory-based applications, including the generation of spectral libraries for classification of biosamples, the identification of biomarkers through large-scale studies, as well as the synthesis and bioactivity assessments of large compound sets necessary for drug discovery. In all these cases, the inherent speed of MS is attractive, but rarely fully utilized due to the widespread use of sample purification techniques prior to analysis. Ambient ionization methodologies can help circumvent this drawback by facilitating highthroughput qualitative and quantitative analysis directly from the complex samples without any need for work-up. For instance, the use of swabs or paper substrates allows for rapid identification, quantification, and confirmation, of drugs of abuse from biofluids or surfaces of forensic interest in a matter of minutes, as described in the first two chapters of this dissertation. Faster analysis can be achieved using an automated desorption electrospray ionization (DESI) platform which allows for the rapid and direct screening of complex-sample microarrays with throughputs better than 1 sample per second, giving access to rich spectral information from tens of thousands of samples per day. The development of the bioanalytical capabilities of this platform, particularly within the context of drug discovery (e.g. bioactivity assays, biosample analysis), is described across most other chapters of this dissertation. The use of DESI, a contactless ambient ionization method developed in our laboratory and whose 20 years of history are overviewed in the introduction of this document, provides an additional advantage as the secondary microdroplets generated through the DESI process act as reaction vessels that can accelerate organic reactions by up to six orders of magnitude, facilitating on-the-fly synthesis of new compounds from arrays of starting materials. Unique implications of this microdroplet chemistry in the prebiotic synthesis of peptides and spontaneous redox chemistry at air-solution interfaces, together with its practical applications to the synthesis of new drug molecules, are also overviewed. The success obtained with the first automated DESI-MS system, developed within the DARPA Make Itprogram, led to increased interest in a new-generation platform which was designed over the past year, as overviewed in the last section of this dissertation, and which is currently being installed for validation prior to the transfer of the technology to NCATS, where we anticipate it will make a significant impact through the consolidation and acceleration of the early drug discovery workflow
Novel mass spectrometric methodologies for in situ detection of hazardous chemical and biological agents
No full textMass spectrometry, widely recognized for its high speed, specificity and sensitivity as well as applicability in the analysis of a broad range of samples, is playing an even-increasingly important role in a broad range of applications. The objectives of the projects described in this thesis research are to develop novel mass spectrometric methodologies for in situ detection of hazardous chemical and biological agents. The first project described is the development and characterization of novel linear ion trap mass analyzers based on the rectilinear geometry. Such mass analyzers consist of either four or six planar electrode and employ pure RF voltages (or with supplementary DC voltages) for two dimensional ion trapping. The structure simplicity makes these devices particularly significant for the development of miniaturized ion trap mass spectrometers. The second project described is the discovery of new ion/molecule reactions and the associated implementation via ambient ionization techniques desorption atmospheric pressure chemical ionization (DAPCI) and desorption electrospray ionization (DESI), for the specificity enhancement in in situ detection of nitroaromatic explosives and organophosphonates. Such additional specificity is especially valuable for in situ chemical hazard detection since complex mixtures are necessarily examined. The third project described is the application of DESI to profile fresh intact microorganisms. This study demonstrates the possibility of performing in situ identification, including sub-species differentiation of microbiological agents by using DESI-MS. The lack of sample treatment and the known sensitivity of the DESI experiment represent progress toward rapid in situ mass spectrometric identification of biological threats. Future directions should include integration of ambient ionizations to miniaturized mass spectrometers, to produce a versatile portable device for in situ detection of chemical and biological threats
Quantitative measurements of chirality and the synthesis of heterocycles in the mass spectrometer
No full textA novel mass spectrometric method for rapid, accurate chiral recognition and enantiomeric determination is presented. The technique uses electrospray ionization on a commercial ion trap mass spectrometer to form transition metal ion-bound cluster ions that promote enantiospecific interactions. Collision induced dissociation (CID) of the cluster ions yields data that is treated by the kinetic method, a sensitive linear free energy method of treating mass spectrometric results and converting them to thermochemical data. Chiral recognition and enantiomeric measurements of amino acids, peptides, α-hydroxy acids, carbohydrates, and some model chiral drugs, including β-blockers, DOPA, and antiviral nucleoside agents, are demonstrated. Two quantitative methods, the single ratio (SR) and quotient ratio (QR) methods, are being developed for enantiomeric determination. A two-point calibration curve based on the SR method, allows rapid quantitation of enantiomeric excess of drug mixtures, while a single-point calibration curve can be established using the QR method. The chiral sensitivity of both quantitative methods is such as to allow determination of mixtures with a few percent enantiomeric contamination with accuracy less than 1%ee. The underlying kinetics, thermochemistry and intrinsic chiral interactions that are responsible for chiral distinction are investigated by tandem mass spectrometry and ab initio calculations. The method is extended to the distinction and quantitative analysis of isomeric mixtures. The analysis of isomeric dipeptides differing in amino acid sequences or residues with the same mass (i.e., a leucine/isoleucine substitution) is demonstrated. The generality of Eberlin reaction is explored using ambiphilic ions including phosphonium, borinium, silylium, and sulfenium cations. Heterocyclic ions are synthesized by a highly exothermic channel, which proceeds via initial cationic binding to a heteroatom followed by a consecutive ring opening and ring reclosing process
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