606 research outputs found
Zheng Ouyang, R. Graham Cooks, and Guangming Huang in laboratory
No full textPurdue University Faculty. From left, Purdue University researchers Zheng Ouyang, an assistant professor of biomedical engineering; R. Graham Cooks, the Henry Bohn Hass distinguished professor of chemistry; and Guangming Huang, a postdoctoral research associate, pose with the mass spectrometer used in a new method for detecting melamine in milk products
R. Graham Cooks and Ismael Cotte-Rodriguez reviewing data
No full textR. Graham Cooks, from left, Purdue's Henry Bohn Hass Distinguished Professor of Analytical Chemistry, works with former doctoral student Ismael Cotte-Rodriguez to review data after using a new miniature mass spectrometer to detect explosives. The portable instrument weighs approximately 22 pounds, is roughly the size of a shoebox and can be installed as part of a remote sensor network to monitor the air in subways, airports or office buildings.College of Science
sj-pdf-2-jla-10.1177_24726303211047839 – Supplemental material for Automated High-Throughput System Combining Small-Scale Synthesis with Bioassays and Reaction Screening
No full textSupplemental material, sj-pdf-2-jla-10.1177_24726303211047839 for Automated High-Throughput System Combining Small-Scale Synthesis with Bioassays and Reaction Screening by Nicolás M. Morato, MyPhuong T. Le, Dylan T. Holden and R. Graham Cooks in SLAS Technology</p
sj-xlsx-1-jla-10.1177_24726303211047839 – for Automated High-Throughput System Combining Small-Scale Synthesis with Bioassays and Reaction Screening
No full textsj-xlsx-1-jla-10.1177_24726303211047839 for Automated High-Throughput System Combining Small-Scale Synthesis with Bioassays and Reaction Screening by Nicolás M. Morato, MyPhuong T. Le, Dylan T. Holden and R. Graham Cooks in SLAS Technology</p
Monitoring of Organic Reactions with and without Accelerated Rates Using Electrospray and Ambient Ionization Mass Spectrometry
No full textCharged microdroplets produced by spray-based ionization techniques such as electrospray ionization have been widely used as a means to probe both reaction mechanisms and kinetics. The same droplets have also been shown to allow increased chemical reactivity compared to corresponding bulk solution-phase kinetics. This apparent conundrum and the exploitation of droplet accelerated reactions were the foci of the work discussed in this dissertation. Controlling variables in the electrospray process as chemical as pH and concentration and as analytical as sheath gas flow and distance between the ion source and the ion transfer capillary of the mass spectrometer have allowed the selection between monitoring reactions by mass spectrometry with or without reaction rate acceleration. Many of these variables have been explored by the Cooks group, the Volmer group at Saarland University (Saarbrücken, Germany) and by the Zare group at Stanford University (Stanford, CA). The well-documented and empirically-backed theoretical models of electrospray ionization support the theories on the cause of reaction rate acceleration by spray-based processes. Using larger Leidenfrost droplets which are created by levitating reaction mixtures of superheated surfaces provides reaction acceleration as well with some similarities to electrospray droplets. Acoustically levitated droplets have also demonstrated the ability to accelerate reactions in small droplets and was used to probe the mechanism of this acceleration. Both adaptations of small volume reactors have potential for scale-up of these reactions and more efficient collections at the cost of lower rate enhancements compared to electrospray ionization processes. The applications of these accelerated reactions include the collection of organic product from the spray process, or more practically from Leidenfrost droplet experiments and screening of novel chemistry in droplets. Using the Leidenfrost experiment it was demonstrated that the synthesis of ca 18 mg of reaction product in the Katritzky pyrylium to pyridinium conversion could be achieved. This makes the Leidenfrost and other levitated droplet techniques an interesting option for scale-up of these accelerated reactions. On the other hand, the factors by which the reactions are accelerated and significantly reduced compared to related thin film and electrospray techniques. Reaction monitoring by electrospray ionization mass spectrometry is a very powerful tool for the investigation of homogeneous reaction mixtures both on-line and off-line. In a collaboration with Amgen Inc., the total synthesis of anagliptin was monitored on-line which provided information on byproducts and reaction completion as well as the ability to track starting materials that were not detectable by traditional methods. Additionally, in this Purdue-Amgen collaboration, a method of chiral analysis by mass spectrometry from reacting systems both off-line and on-line was developed and implemented on reaction systems of interest to Amgen (an enantioselective N-alkylation reaction and the base-catalyzed racemization of ibuprofen). Chiral analysis by mass spectrometry involves the creation of metal-coordinated diastereomeric cluster ions in the process of electrospray ionization which then can give rise to different abundances of product ions upon low-energy gas-phase dissociation of the isolated diastereomeric cluster ion. This method of chiral analysis by tandem mass spectrometry had been previously published but this was the first time this method had been applied to on-line or off-line reaction monitoring
Environmental analysis and on-line monitoring: Applications of membrane introduction mass spectrometry
No full textProcess analysis and environmental analysis are two areas of growing scientific and technological importance. The applicability of membrane introduction mass spectrometric systems utilizing flow-through membrane probes to these applications forms the subject of this thesis. A simple membrane probe interfaced to a commercial quadrupole ion trap detector was used for environmental analysis. This system exhibited fast response times and showed low part-per-billion detection limits for a set of nine organic compounds. Quantitation of well-water samples using the membrane/ion trap system gave agreement with measurements obtained by standard gas chromatographic procedures. These results demonstrate the feasibility of using an ion trap detector interfaced with a membrane probe for water analysis at low levels. A flow injection analysis system was used for on-line monitoring of bioreactors. This system incorporated a sheet direct insertion membrane probe and utilized a triple quadrupole mass spectrometer. Up to fifteen samples of fermentation medium per hour could be quantitated on-line with this system and concentration measurements of liquid-phase products agreed with values measured off-line by gas chromatography. The tandem mass spectrometric capabilities of the triple quadrupole mass spectrometer were used to identify trace metabolites including acetone. The two micro-organisms of interest, Bacillus polymyxa and Klebsiella oxytoca, produce both meso- and R,R-()-2,3-butanediol. Capabilities for isomer distinction were added to the on-line monitoring system by on-line derivatization. 2,3-Buanediol was derivatized using phenyl boric acid to produce a phenyl boric ester which was stable in an aqueous environment and could be used to distinguish the diastereomers. Chemical ionization followed by dissociation of the protonated molecular ions provided the desired isomer distinction. The effects of collision energy and collision pressure were investigated to determine optimal conditions for diastereomer distinction and to gain insight into fragmentation pathways
Applications of desorption chemical ionization tandem mass spectrometry
No full textFour different chemical investigations are undertaken by implementing desorption chemical ionization tandem mass spectrometry (DCI-MS/MS) with a Finnigan TSQ 700 mass spectrometer. A method was developed for the rapid quantitation of the anticancer drug taxol and the analogs cephalomannine and baccatin III using d\sb3-internal standards. With this method, crude plant extracts can be screened for these three target taxanes at the femtomole level with a 12% relative standard deviation in less than five minutes per sample. Various MS/MS scans are also described for the identification of novel analogs of taxol. Derivatization of buckminsterfullerene is studied in the condensed phase by various mechanisms of carbon-carbon bond formation including photochemical, nucleophilic, (2+2) cyclo- and diradical addition. Products are characterized by DCI-MS and DCI-MS/MS. Fullerene reactivity is also studied in the gas phase, including Diels-Alder (4+2) cycloaddition and adduct formation with carbocations, halides and hydrogen in the chemical ionization source. Application of the kinetic method to the determination of free radical proton affinities is demonstrated. The proton affinity of phenoxyl was determined to be 205.6 0.3 kcal/mol which is in agreement with a thermochemical cycle value of 204.8 2.0 kcal/mol. The proton affinities of various substituted phenoxyl radicals were measured and compared with thermochemical cycle values and the results of ab initio calculations. In addition, DCI-MS/MS is used for structure differentiation of isobaric ions by proton affinity measurement. The microstructure of alkyl isocyanate copolymers comprised of (R)- and (S)-monomers is determined by incorporation of a mirror image selective label, deuterium, into the (S)-enantiomer. The mass spectrometric analysis of the copolymers produced by polymerization of these enantiomers reveals that the monomers units are randomly distributed. These results, along with empirical force field calculations and optical analyses, lead to the conclusion that the handedness of the poly(alkyl isocyanate) helical coil is determined by the majority isomer and that the minority isomer is inserted, randomly, into this coil
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
- …
