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At least 19 recordsLinked to original sources
PubMed2004

Development of an ion mobility spectrometer for use in an atmospheric pressure ionization ion mobility spectrometer/mass spectrometer instrument for fast screening analysis.

An ion mobility spectrometer that can easily be installed as an intermediate component between a commercial triple-quadrupole mass spectrometer and its original atmospheric pressure ionization (API) sources was developed. The curtain gas from the mass spectrometer is also used as the ion mobility spectrometer drift gas. The design of the ion mobility spectrometer allows reasonably fast installation (about 1 h), and thus the ion mobility spectrometer can be considered as an accessory of the mass spectrometer. The ion mobility spectrometer module can also be used as an independently operated device when equipped with a Faraday cup detector. The drift tube of the ion mobility spectrometer module consists of inlet, desolvation, drift, and extraction regions. The desolvation, drift and extraction regions are separated by ion gates. The inlet region has the shape of a stainless steel cup equipped with a small orifice. Ion mobility spectrometer drift gas is introduced through a curtain gas line from an original flange of the mass spectrometer. After passing through the drift tube, the drift gas serves as a curtain gas for the ion-sampling orifice of the ion mobility spectrometer before entering the ion source. Counterflow of the drift gas improves evaporation of the solvent from the electrosprayed sample. Drift gas is pumped away from the ion source through the original exhaust orifice of the ion source. Initial characterization of the ion mobility spectrometer device includes determination of resolving power values for a selected set of test compounds, separation of a simple mixture, and comparison of the sensitivity of the electrospray ionization ion mobility spectrometry/mass spectrometry (ESI-IMS/MS) mode with that of the ESI-MS mode. A resolving power of 80 was measured for 2,6-di-tert-butylpyridine in a 333 V/cm drift field at room temperature and with a 0.2 ms ion gate opening time. The resolving power was shown to be dependent on drift gas flow rate for all studied ion gate opening times. Resolving power improved as the drift gas flow increased, e.g. at a 0.5 ms gate opening time, a resolving power of 31 was obtained with a 0.65 L/min flow rate and 47 with a 1.3 L/min flow rate for tetrabutylammonium iodide. The measured limits of detection with ESI-MS and with ESI-IMS/MS modes were similar, demonstrating that signal losses in the IMS device are minimal when it is operated in a continuous flow mode. Based on these preliminary results, the IMS/MS instrument is anticipated to have potential for fast screening analysis that can be applied, for example, in environmental and drug analysis.

Journal Article↗
PubMed2000

A Designed beta-Hairpin Containing a Natural Hydrophobic Cluster This research was supported by the National Science Foundation (CHE-9820952). J.F.E. was supported by a fellowship from the Ministerio de Educacion y Cultura (Spain) and the Fulbright Commission. The mass spectrometer was purchased in part with a National Science Foundation grant (CHE-9520868), and the NMR spectrometers were purchased in part with a National Institute Of Health grant (1 S10 RR04981). The CD spectrometer and analytical ultracentrifuge are part of the UW Biophysics Instrumentation Facility (NSF BIR-9512577).

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Journal Article↗
PubMed1997

Synchronized scanning of the first and second mass spectrometers on tandem double-focusing mass spectrometers.

A method is described to synchronize the scans of the first and second double-focusing mass spectrometers of a tandem double-focusing mass spectrometer. The scans are synchronized by scanning the first mass spectrometer with voltages instead of the magnetic field. The method is demonstrated with scans that provide all of the precursor ions that produce a selected product ion (precursor ion scan). These precursor ion scans are compared to the previous method of obtaining precursor ion scans on a tandem double-focusing mass spectrometer. The precursor ion scans using the synchronized scanning allow for the use of high-energy collisions on any tandem double-focusing mass spectrometer, while limiting the mass range possible in a single scan. The limited mass range may be corrected by obtaining several spectra with different magnetic fields on the first mass spectrometer.

Mass Spectrometry↗
PubMed2006

Modeling of the generic spatial heterodyne spectrometer and comparison with conventional spectrometer.

We describe the modeling of the generic spatial heterodyne spectrometer. This instrument resembles a somewhat modified Michelson interferometer, in which the power spectrum of the input source is determined by performing a one-dimensional Fourier transform on the output intensity profile. Code has been developed to analyze the performance of this type of spectrometer by determining the dependence of both spectral resolution and throughput on parameters such as aperture and field of view. An example of a heterodyne spectrometer is developed to illustrate the techniques employed in the modeling and a comparison undertaken between its performance and that of a conventional spectrometer. Unlike the traditional Fourier transform infrared system, the heterodyne spectrometer has the very desirable feature of having no moving components.

Journal Article↗
PubMed2003

A pulsed corona discharge switchable high resolution ion mobility spectrometer-mass spectrometer.

A pulsed corona discharge ionisation source, a candidate replacement for 63Ni ionisation sources for ion mobility spectrometry, is described along with a new design of ion mobility spectrometer-mass spectrometer. Preliminary research on the characterisation of the reactant ion peaks associated with the use of this ionisation source was undertaken by assembling a pulsed corona discharge ionisation switchable high-resolution ion mobility spectrometer-mass spectrometer to enable the mobility spectra, atmospheric chemical ionisation mass spectra and selected-mass mobility spectra to be obtained. With ammonia doping at 2.39 mg m(-3) in air and a water content of approximately 80 mg m(-3) in the positive mode the observed response was attributable to the formation of 1(H2O)(n)NH4]+ and [(H2O)n(NH3)NH4]+ in the reaction region. The observed responses in the negative mode were more complex with evidence for the formation [(H2O)(n)O2]-, [(H2O)(n)CO3]-, [(H2O)(n)HCO3]-, [(H2O)(n)CO4]- and [(H2O)(n)NO3]-. The responses due to these species were clearly discernible in the resultant mobility spectra, with enough oxygen-based species formed to support analytically useful responses.

Journal Article↗
PubMedDate not supplied

High sensitivity identification of proteins by electrospray ionization tandem mass spectrometry: initial comparison between an ion trap mass spectrometer and a triple quadrupole mass spectrometer.

Recently, we have shown that a solid-phase-microextraction/capillary electrophoresis device coupled to an electrospray ionization triple quadrupole mass spectrometer through a microelectrospray interface represents a powerful analytical system for the rapid, conclusive and sensitive identification of proteins separated by gel electrophoresis. Here we report on the successful coupling of the same device to an electrospray ionization ion trap mass spectrometer and on the comparative evaluation of the performance of the triple quadrupole and ion-trap-based systems. In the ion trap mass spectrometer-based system, using a tryptic digest of a calibrated bovine serum albumin sample, we achieved limits of detection in the single mass spectrometry (MS) and tandem MS mode, respectively, of 400 amol (if 20 microL of solution at a concentration of 20 amol/microL was applied). The system was also successfully used to identify six yeast proteins isolated from a single analytical two-dimensional polyacrylamide gel. For the detection of unfragmented peptide ions both systems showed comparable sensitivity, whereas the ion-trap-based system showed superior performance with fragment ion spectra.

Amino Acid Sequence↗
PubMed2003

[Comparison between two 13C-urea breath tests for the diagnosis of Helicobacter pylori infection: isotope ratio mass spectrometer versus infrared spectrometer].

OBJECTIVES: To compare the accuracy of the breath test using the isotope ratio mass spectrometer (IRMS) versus the nondispersive isotope-selective infrared spectrometer (NDIRS) in the diagnosis of Helicobacter pylori infection. METHOD: Multicenter study in 4 Spanish hospitals. One group of dyspeptic patients who had not undergone prior eradication therapy and another group of patients with gastric ulcer or gastrointestinal bleeding due to gastroduodenal ulcer receiving H. pylori eradication therapy were included in the study. A reference standard based on histology and the rapid urease test was used. The breast test (TAU-KIT, Isomed S.L., Madrid, Spain) was performed with citric acid and 100 mg of 13C-urea. Samples of expired air were collected in tubes and bags for reading with the IRMS (ABCA, PDZ, Crewe, Manchester, England) and the NDIRS (UBiT-IR200, Otsuka Electronics, Co, Osaka, Japan), respectively. The endoscopist, pathologist and person responsible for reading the urease test and both breath tests were blinded to the results of the other diagnostic methods. RESULTS: Forty-one patients were included. The prevalence of H. pylori was 26%. No differences were found on comparing the mean values obtained with the IRMS and the NDIRS: 13 (standard deviation) (24) and 14 (25) delta units, respectively. The area under the ROC curve for the IRMS and the NDIRS was 0.96. The diagnostic accuracy for the best cut-off point with the IRMS and the NDIRS was, respectively: sensitivity (90 and 100%), specificity (96 and 89%), positive predictive value (90 and 77%), negative predictive value (96 and 100%), + likelihaod ratio (25 and 9.3) and (0.1 and 0). A close correlation was found between the values of the IRMS and those of the NDIRS (lineal regression equation, Y = 1.1 + 1.004. X; r = 0.97). CONCLUSION: Both the spectrometers used to evaluate the breath test, the IRMS and the NDIRS, offer a high degree of accuracy in the diagnosis of H. pylori infection.

Breath Tests↗
PubMed2003

A comparison of the quantitative methods for the analysis of the platinum-containing anticancer drug [cis-[amminedichloro(2-methylpyridine)]platinum(II)] (ZD0473) by HPLC coupled to either a triple quadrupole mass spectrometer or an inductively coupled plasma mass spectrometer.

The use of high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICPMS) as means for the quantitative determination of ZD0473, a platinum anticancer drug, and its related biologically active "aqua" compounds in biofluid samples is described. The performance of the resulting HPLC-ICPMS method was compared with that of a conventional HPLC-triple quadrupole mass spectrometer-based (HPLC-MS/MS) system for properties such as limit of detection, linearity, and reproducibility using spiked samples. The methods were then applied to the determination of plasma ultrafitrate concentrations of ZD0473 in dog plasma samples obtained following intravenous and oral administration at 0.5 and 6 mg/kg, respectively. These experiments showed that both methods were capable of providing accurate and precise results but that the HPLC-ICPMS method had advantages of extended linear range and superior sensitivity, providing a limit of quantification of 0.1 ng/mL for ZD0473, as compared to 5 ng/mL using the current HPLC-MS/MS method. In addition, by using a single combined HPLC-ICPMS/MS/MS system, it was possible to determine the relative MS/MS response of the aqua compounds for the first time.

Animals↗
PubMed2005

Pulsed oscillating mass spectrometer: a miniaturized type of time-of-flight mass spectrometer.

We report the development, characterization, and performance of a new type of time-of-flight mass analyzer that employs an oscillatory ion flight path and uses secondary electrons to record the mass spectrum. The analyzer is simple in concept and design and inexpensive to build and has been made as small as 6-cm total length. The oscillating ions produce a periodic secondary electron signal whose frequency is mass dependent in mathematically the same way as a conventional time-of-flight analyzer. Because of the oscillating nature of the ions, we have called the analyzer the pulsed oscillating mass spectrometer.

Journal Article↗
PubMed2006

Using a nanoelectrospray-differential mobility spectrometer-mass spectrometer system for the analysis of oligosaccharides with solvent selected control over ESI aggregate ion formation.

Differential mobility spectrometry (DMS), also commonly referred to as high field asymmetric waveform ion mobility spectrometry (FAIMS) is a rapidly advancing technology for gas-phase ion separation. The interfacing of DMS with mass spectrometry (MS) offers potential advantages over the use of mass spectrometry alone. Such advantages include improvements to mass spectral signal/noise, orthogonal/complementary ion separation to mass spectrometry, enhanced ion and complexation structural analysis, and the potential for rapid analyte quantitation. In this report, we demonstrate the successful use of our nanoESI-DMS-MS system, with a methanol drift gas modifier, for the separation of oligosaccharides. The tendency for ESI to form oligosaccharide aggregate ions and the negative impact this has on nanoESI-DMS-MS oligosaccharide analysis is described. In addition, we demonstrate the importance of sample solvent selection for controlling nanoESI oligosaccharide aggregate ion formation and its effect on glycan ionization and DMS separation. The successful use of a tetrachloroethane/methanol solvent solution to reduce ESI oligosaccharide aggregate ion formation while efficiently forming a dominant MH(+) molecular ion is presented. By reducing aggregate ion formation in favor of a dominant MH(+) ion, DMS selectivity and specificity is improved. In addition to DMS, we would expect the reduction in aggregate ion complexity to be beneficial to the analysis of oligosaccharides for other post-ESI separation techniques such as mass spectrometry and ion mobility. The solvent selected control over MH(+) molecular ion formation, offered by the use of the tetrachloroethane/methanol solvent, also holds promise for enhancing MS/MS structural characterization analysis of glycans.

Mass Spectrometry↗
PubMed2001

Wavelength Dispersive Spectrometer and Energy Dispersive Spectrometer Automation: Past and Future Development.

As part of the Microbeam Analysis Society (MAS) symposium marking 50 years of electron microprobe analysis, this article reviews the important advances made over the decades to the automation of data collection and computerized analysis of data from the electron microprobe. Out of many innovations that contributed to the advance of microprobe automation, we have chosen to focus on a few developments that the authors feel represent the major trends in advancement of the "state of the art" of this instrumentation. After providing brief summaries of the three generations of advances in the hardware and software of automation systems, several key applications developments are described, followed by our prediction of which current developments may impact the future automation of the microprobe.

Journal Article↗
PubMed2006

Rapid separation and quantitative analysis of peptides using a new nanoelectrospray- differential mobility spectrometer-mass spectrometer system.

Differential mobility spectrometry (DMS) (see Buryakov, I. A.; Krylov, E. V.; Nazarov, E. G.; Rasulev, U. Kh. Int. J. Mass Spectrom. Ion Processes 1993, 128, 143-148), also commonly referred to as high-field asymmetric waveform ion mobility spectrometry (FAIMS) (see Purves, R. W.; Guevremont, R.; Day, S.; Pipich, C. W.; Matyjaszcyk, M. S. Rev. Sci. Instrum. 1998, 69, 4094-4105), is a rapidly advancing technology for gas-phase ion separation. The interfacing of DMS with mass spectrometry (MS) offers potential advantages over the use of mass spectrometry alone. Such advantages include improvements to mass spectral signal-to-noise, orthogonal/complementary ion separation to mass spectrometry, enhanced ion and complexation structural analysis, and the potential for rapid analyte quantitation. In this report, we investigate the use of our nanoESI-DMS-MS system to demonstrate differential mobility separation of peptides. The formation of higher order peptide aggregate ions (ion complexes) via electrospray ionization and the negative impact this has on DMS peptide separation are examined. The successful use of differential mobility drift gas modifiers (dopants) to reduce aggregate ion size and improve DMS peptide ion separation is presented. Following optimization of DMS peptide separation conditions, we examined next the feasibility of a new analytical platform which uses direct sample infusion with nanoESI-DMS-MS for ultrarapid analyte quantitation. Quantitation of a selected peptide from a semicomplex peptide mixture is presented. Initial feasibility results with this new approach demonstrate good accuracy and reproducibility, as well as an absolute mass sensitivity of 6.8 amol and a minimum dynamic range of 2500 for the peptide of interest. This report offers a first look at utilizing nanoESI-DMS-MS to create an ultrarapid (under 5 s) quantitative analysis platform and its potential in the high-throughput arena. Each ion separation technique, DMS and MS, offers orthogonal ion separation to one another, enhancing the overall specificity for this quantitative approach.

Mass Spectrometry↗
PubMed1996

A foil-mask spectrometer for laue pattern imaging: simultaneous position, intensity and energy.

An X-ray spectrometer for simultaneous position, intensity and energy determinations suitable for Laue diffraction applications is described. The foil-mask spectrometer consists of a series of metal foils of varying composition and thickness which are used to modulate the energy distribution of an incident X-ray source. Three modes of operation are described: a high-resolution spectrometer for measurement of nearly monochromatic X-rays, an intensity discriminator for partitioning the intensity from a small number of spatially overlapped monochromatic X-ray sources, and a low-resolution spectrometer for polychromatic X-rays with broad spectral features. The first mode of operation is designed to allow the energy of monochromatic Laue reflections to be measured with a resolution suitable for determination of unit-cell parameters. The second mode of operation is designed to allow the intensity of each component in a spatial region containing overlapping orders or spatially overlapped reflections to be discriminated for use in refinements or space-group assignment. The third mode of operation is described for completeness. The theory behind each mode of operation is described. The energy resolution of the spectrometer improves with the square root of the intensity of the incident beam. It also increases linearly with the change in energy with respect to transmission efficiency of a particular foil. In theory, the resolution of the spectrometer can readily exceed 50 eV over a wide range of energies depending on the foils used and the incident X-ray photon flux. Determinations of the energies of Mo Kalpha and Cu Kalpha radiation using a first-generation ten-foil spectrometer gave values of 17.5 +/- 0.1 and 8.08 +/- 0.05 keV, respectively. Treatment of random error shows good correspondence with a Poisson model. The use of this spectrometer is demonstrated using a sample of tetraphenylphosphonium tetrachlorooxomolybdenum(V). Comparison of predicted and observed energies shows good agreement over a wide range of energies. The ratio of predicted to measured energy for the first 50 measurements was 0.9918+/-0.0344. Up to three components of a position having harmonic overlap were separated. This work demonstrates the feasibility of using Laue diffraction to completely determine the crystal structure of a molecule without recourse to monochromatic methods.

Journal Article↗
PubMed1991

Evaluation of a single-room, dedicated mass spectrometer.

A single-room dedicated mass spectrometer can be used to measure carbon dioxide, halogenated anesthetic agents, nitrous oxide, nitrogen, and oxygen. This device challenges the multiplexed mass spectrometer, a current standard in measurement. This study compared the single-room dedicated mass spectrometer with a conventional mass spectrometer that is normally used in a multiplexed setting. In this study, a single-room dedicated Ohmeda 6000 Mini-Mass Spectrometer and the Perkin-Elmer MGA-1100 mass spectrometer were calibrated with the same reference gases and both devices sampled various concentrations of dry gases. Regression lines and intercepts were plotted and showed excellent correlation between the two devices. The intraclass correlation test of Lee, Koh, and Ong, showed the devices to be equivalent with regard to the ability to determine various gas concentrations. Various advantages of a single-room dedicated mass spectrometer are discussed.

Anesthesiology↗
PubMed2006

Analysis of slitless holographic spectrometers implemented by spherical beam volume holograms.

The analysis of a slitless volume holographic spectrometer is presented in detail. The spectrometer is based on a spherical beam volume hologram followed by a Fourier-transforming lens and a CCD. It is shown that the spectrometer is not sensitive to the incident angle of the input beam for the practical range of applications. A holographic spectrometer based on the conventional implementation is also analyzed, and the results are used to compare the performance of the proposed method with the conventional one. The experimental results are consistent with the theoretical study. It is also shown that the slitless volume holographic spectrometer lumps three elements (the entrance slit, the collimator, and the diffractive element) of the conventional spectrometer into one spherical beam volume hologram. Based on the unique features of the slitless volume holographic spectrometer, we believe it is a good candidate for portable spectroscopy for environmental and biological applications.

Algorithms↗
PubMed2000

The virtual NMR spectrometer: a computer program for efficient simulation of NMR experiments involving pulsed field gradients.

This paper presents a software program, the Virtual NMR Spectrometer, for computer simulation of multichannel, multidimensional NMR experiments on user-defined spin systems. The program is capable of reproducing most features of the modern NMR experiment, including homo- and heteronuclear pulse sequences, phase cycling, pulsed field gradients, and shaped pulses. Two different approaches are implemented to simulate the effect of pulsed field gradients on coherence selection, an explicit calculation of all coherence transfer pathways, and an effective approximate method using integration over multiple positions in the sample. The applications of the Virtual NMR Spectrometer are illustrated using homonuclear COSY and DQF COSY experiments with gradient selection, heteronuclear HSQC, and TROSY. The program uses an intuitive graphical user interface, which resembles the appearance and operation of a real spectrometer. A translator is used to allow the user to design pulse sequences with the same programming language used in the actual experiment on a real spectrometer. The Virtual NMR Spectrometer is designed as a useful tool for developing new NMR experiments and for tuning and adjusting the experimental setup for existing ones prior to running costly NMR experiments, in order to reduce the setup time on a real spectrometer. It will also be a useful aid for learning the general principles of magnetic resonance and contemporary innovations in NMR pulse sequence design.

Algorithms↗
PubMed2002

Design and implementation of a protection system for NMR spectrometers.

We have implemented a scheme, SPECMON, for monitoring various parameters of a spectrometer, such as nitrogen pressure and sample temperature, and taking corrective action. The scheme is based on considerations of protection management which are of general application. Evaluation of the spectrometer state is incorporated in macros of the application software (VNMR) and is therefore very flexible. In contrast, corrective action is limited to the single one which is deemed fully safe: complete shutdown of the spectrometer and logging. Shutdown is implemented by a minor hardware modification of the spectrometer: the introduction of a second input to a relay already present for protection of the spectrometer power supply. Monitoring is handled by the host computer, and the shutdown command is transmitted via control lines of its series port, independent of the standard connection between the host computer and the NMR system console. The monitoring system (software and hardware) is unobtrusive in normal conditions, and it can be tested without affecting the operation of the spectrometer.

Journal Article↗
PubMed2000

Evaluation of open-path FTIR spectrometers for monitoring multiple chemicals in air.

There has been mounting interest in the use of open-path Fourier transform infrared (OP-FTIR) spectrometers for occupational and environmental air monitoring. Although this technology is gaining acceptance in the environmental field, there has not yet been a comprehensive assessment of instrument performance and the analytical limitations of this method have not been thoroughly delineated. Unlike extractive FTIR spectrometers, calibration of OP-FTIR spectrometer systems presents unique problems because the optical beam is exposed to the atmosphere. Therefore, it is difficult to get an adequate clean background and perform evaluation tests used by extractive instruments. One solution to the problem of evaluating an open-path system is to place a sample cell directly in the path of the infrared beam. The purpose of this study was to investigate the use of a specially designed external calibration cell as a tool for laboratory and field evaluation of the accuracy of OP-FTIR spectrometers and to investigate various commonly used instrument performance parameters such as root mean square (RMS) noise, return intensity, instrument precision, and detector saturation. These performance parameters were measured to see if they could be used to predict whether an instrument is operating correctly. Six instruments from the same manufacturer were evaluated with a prototype calibration cell using NIST traceable sulfur hexafluoride, n-hexane, and cyclohexane. Reference concentrations generated in the calibration cell were compared with OP-FTIR spectrometer measured concentrations measured through the cell. Excellent correlation and slopes were obtained for all three chemicals. The instrument performance measures could not be used to predict accuracy. The external calibration cell shows promise as a method of validating the operation of an OP-FTIR spectrometer for quality assurance and for quality control.

Air Pollution↗