An ion-storage time-of-flight mass spectrometer for analysis of electrospray ions.

A preliminary design and implementation of a novel approach to electrospray-mass spectrometry are described. Based on a time-of-flight mass analysis, the instrument provides several important advantages for on-line mass analysis: 1, simplicity, ease of use and low manufacturing cost; 2, rapid scan speed, yielding quasi-instantaneous full mass scans at repetition rates up to several kHz; 3, soft ionization and accurate mass determination of extremely large analyte molecules; 4, high sensitivity.     

Excitation temperatures of atoms and ions in a hollow cathode discharge

Excitation temperatures have been measured in a hollow cathode discharge from intensities of Ar I, Ar II, Ti I, Ti II, AI I, Mg I, Mg II, Cu I and Pb I lines. The differences between values derived from the species listed are discussed.     

Semiquantitative multielemental analysis of biological samples by a laser ionization orthogonal time-of-flight mass spectrometer

Semiquantitative multielemental analyses of biological samples (tea leaf standard, Laminaria japonica, and pig skin) were demonstrated with a newly developed laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS). The sample was directly ablated and ionized with high irradiance after simple sample preparation. Relative sensitivity coefficients (RSC) were calculated and evaluated for sensitivity differences. Due to the employment of a collisional cooling device and the orthogonal geometry of the TOF system, high resolving power can be obtained, such that elemental peaks and interferential peaks with the same nominal mass can be distinguished. The detection limit of μg g⁻¹ levels can be commonly achieved for elemental determination.     

Analysis of solid uranium samples using a small mass spectrometer

A mass spectrometer for isotopic analysis of solid uranium samples has been constructed and evaluated. This system employs the fluorinating agent chlorine trifluoride (ClF₃) to convert solid uranium samples into their volatile uranium hexafluorides (UF₆). The majority of unwanted gaseous byproducts and remaining ClF₃ are removed from the sample vessel by condensing the UF₆ and then pumping away the unwanted gases. The UF₆ gas is then introduced into a quadrupole mass spectrometer and ionized by electron impact ionization. The doubly charged bare metal uranium ion (U²⁺) is used to determine the U²³⁵/U²³⁸ isotopic ratio. Precision and accuracy for several isotopic standards were found to be better than 12%, without further calibration of the system. The analysis can be completed in 25 min from sample loading, to UF₆ reaction, to mass spectral analysis. The method is amenable to uranium solid matrices, and other actinides.     

Design and performance of a desktop time-of-flight mass spectrometer for analyzing metal ions

We have described a home-made desktop orthogonal-injection time-of-flight (O-ToF) mass spectrometer combining a collisional cooling system. This O-ToF consists of a simple electrospray ion source, an atmosphere-vacuum interface, an area of transmission, including a radio-frequency only quadrupole (RF- only quadrupole, RFQ) as a collisional cooling cell and an orthogonal ToF mass analyzer. In order to detect ions of small m/z value, such as small metal ions, the RFQ has been improved to weaken the mass discrimination effect against low mass ions. Metal salt solutions were used in the experiment. The system has shown a satisfactory resolving power in the spectra (m/Δm = 3500), a good mass stability, a limit of detection of 80 fg and a mass accuracy of 48 ppm. The dynamic range is found to be from 10(-8) mol L(-1) to 10(-5) mol L(-1), allowing the semi-quantitative analysis of metal ions.     

The use of a secondary cathode to analyse solid non-conducting samples with direct current glow discharge mass spectrometry: potential and restrictions

A direct current glow discharge mass spectrometer has been used to analyse solid non-conducting samples: glass, polycarbonate, marble, aluminium oxide and Teflon. This is made possible by the use of a so-called secondary cathode. The methodology of this concept is investigated and analytical figures of merit are presented.     

The use of a secondary cathode to analyse solid non-conducting samples with direct current glow discharge mass spectrometry: potential and restrictions

A direct current glow discharge mass spectrometer has been used to analyse solid non-conducting samples: glass, polycarbonate, marble, aluminium oxide and Teflon. This is made possible by the use of a so-called secondary cathode. The methodology of this concept is investigated and analytical figures of merit are presented.     

Model of microsecond pulsed glow discharge in hollow cathode for mass spectrometry

A new model for microsecond pulsed glow discharge in a hollow cathode and its afterglow is described. The model is based on the Monte-Carlo method together with a new method for electrical field calculation, which is based on some phenomenological laws of plasma behavior. The afterglow model uses continuity and Poisson equations. A qualitative agreement between the model results and results published in experimental and theoretical works is demonstrated. Some processes in the microsecond pulsed discharge in the hollow cathode, such as sputtering, ionization and transfer of sample, are investigated. The model is successfully used for the optimization of the operational parameters of the time-of-flight mass spectrometer with ionization by microsecond pulsed glow discharge in a hollow cathode.     

Exact mass measurement of product ions for the structural elucidation of drug metabolites with a tandem quadrupole orthogonal-acceleration time-of-flight mass spectrometer

We herein report upon an approach whereby the interpretation of tandem mass spectrometry spectra can be both expedited and simplified via the accurate mass assignment of product ions utilizing a tandem quadrupole time-of-flight mass spectrometer (QqTOF). The applicability of the QqTOF in the drug metabolism laboratory is illustrated by the elucidation and differentiation of the dissociative pathways for Bosentan and its hydroxylated and demethylated metabolites. Target analyte fragmentation mechanisms were readily achieved by the measurement of product ions with a mass accuracy <5 ppm, possible by single-point internal recalibration using the residual precursor ion as calibrant. Differentiation of both precursor and product ions from nominally isobaric matrix species derived from biological extracts is demonstrated by operation of the QqTOF at resolutions of 8000 (m/Δm_FWHM).     

Lumas-30 time-of-flight mass spectrometer with pulsed glow discharge for direct determination of nitrogen in steel

The problem of quantitative determination of nitrogen in steel has become one of the main tasks in modern metallurgy due to the intensive use of nitrogen as an alloy additive. The presence of such additives is known to improve a number of steel characteristics (corrosion resistance, nonmagnetic behavior, strength, etc.). Both direct and indirect analytical methods have many disadvantages and call for revision. The direct technique of nitrogen determination in steel using a a pulsed glow discharge time-of-flight mass spectrometry is proposed in this paper. Successful application of the method for steel samples with different nitrogen concentrations was demonstrated. Dependence of the nitrogen signal intensity as a function of the repelling pulse delay was investigated, and the optimal delay time was obtained. The detection limit of for the proposed method was found to be 0.03%.     

Complex mixture analysis based on gas chromatography-mass spectrometry with time array detection using a beam deflection time-of-flight mass spectrometer

A beam deflection time-of-flight mass spectrometer was developed in conjunction with an integrating transient recorder to provide time array detection, permitting high mass spectral scan file acquisition rates for complex mixture analysis by capillary gas chromatography-mass spectrometry (GC-MS). Results are presented for the analysis of a urinary organic acid mixture by GC-MS at a scan file acquisition rate of 10 scan files per second (sf/s), showing the advantages of such data collection in the deconvolution of partially resolved components. The reconstructed total ion current (RTIC) chromatogram available from data acquired at this scan file generation rate is shown to be comparable to the profile obtained from a flame ionization detector in representing the chromatography performed under identical experimental parameters. The RTIC chromatogram available from the database obtained at 10 sf/s is compared with that available from a database obtained at 1 sf/s, the latter representing that scan rate typically used with most GC-MS instruments. The advantages of the higher scan file acquisition rate in representing the chromatographic profile and in allowing mass spectral data to be obtained for components in the complex mixture that are unresolved chromatographically are discussed.     

A tandem time-of-flight mass spectrometer: combination of a multi-turn time-of-flight and a quadratic-field mirror

A tandem time-of-flight (ToF) mass spectrometer consisting of a multi-turn time-of-flight (ToF) and a quadratic-field ion mirror has been designed and constructed. The instrument combines the unique capabilities of both ToF instruments, namely high-resolution and monoisotopic precursor ion selection from the multi-turn ToF and temporal focus for fragment ions with different kinetic energies from the quadratic-field mirror. The first tandem mass spectra for this unique combination of ToF systems are presented.     

Detection of negative ions in glow discharge mass spectrometry for analysis of solid specimens

A new method is presented for elemental and molecular analysis of halogen-containing samples by glow discharge time-of-flight mass spectrometry, consisting of detection of negative ions from a pulsed RF glow discharge in argon. Analyte signals are mainly extracted from the afterglow regime of the discharge, where the cross section for electron attachment increases. The formation of negative ions from sputtering of metals and metal oxides is compared with that for positive ions. It is shown that the negative ion signals of F^? and TaO₂F^? are enhanced relative to positive ion signals and can be used to study the distribution of a tantalum fluoride layer within the anodized tantala layer. Further, comparison is made with data obtained using glow-discharge optical emission spectroscopy, where elemental fluorine can only be detected using a neon plasma. The ionization mechanisms responsible for the formation of negative ions in glow discharge time-of-flight mass spectrometry are briefly discussed.     

High-resolution mass spectrometry of large molecules in a linear time-of-flight mass spectrometer

This report describes a new high-resolution linear time-of-flight mass spectrometer that has been constructed at this institute. The instrument is used for investigations of both direct and matrix-assisted laser desorption/ionization of large molecules. A unique feature of this new instrument is the incorporation of a 10-cm postsource pulse-focusing region for enhancing the resolution of the detected ion signals. This technique can correct for both high initial ion translational energies and long durations of ion formation and is expected to be particularly well suited for laser desorption/ionization applications. Results of calculations are presented to illustrate the gains in mass resolution that may be expected for a variety of ion formation conditions. In addition, initial experimental results are presented that demonstrate the capability of this new instrument to produce high-resolution ion signals. Signals with mass resolutions as high as 2750 (full width at half maximum) have been obtained for both direct and matrix-assisted laser desorption/ionization signals.     

Development of a supercritical fluid extractor coupled with a time-of-flight mass spectrometer for online detection of extracts.

A combined apparatus of a supercritical CO2 extractor (SFE) and a time-of-flight mass spectrometer (TOF-MS) was developed aiming at the direct analysis of extracts. A fused-silica capillary acts as both a pressure restrictor and an effluent injection nozzle into the TOF-MS. The tip of the nozzle was narrowed by melting and abrasion so that a greater pressure drop occurred at the tip. In the TOF-MS chamber, differential pumping between the main and ionization chamber kept the pressure in the ionization chamber at around 10(-3) Pa when the SFE pressure was at 9.7 to 29.4 MPa. The TOF-MS performance, a mass resolution of 263 at m/z = 146, and a sensitivity of 1.6 ng (p-dichlorobenzene) were certified by direct injection of a standard organic solution. Online detection of SFE effluent containing naphthalene, p-dichlorobenzene, phenanthrene and pyrene were successfully performed by the TOF-MS only for 48000 ionization cycles corresponding to 7.5 s.     

High resolution spectroscopy of iridium in a hollow cathode discharge

We demonstrate the possibility of performing high resolution laser spectroscopy of iridium atoms produced by sputtering in a hollow cathode discharge. By resolving the hyperfine structure of ultraviolet transitions from the ground state, we measure the magnetic dipole and electric quadrupole constants of the 5d ⁷ 6s 6p ⁶ G _11/2 and 5d ⁷ 6s 6p ⁶ F _7/2 excited levels and we obtain accurate values for the isotope shifts. Iridium is also discussed as possibly providing reference spectra in the 243 nm region, close to the wavelength of the 1s–2s two-photon transition of hydrogen.     

Depth profile analysis of surface modified SnO2 gas sensors in a hollow cathode discharge

Depth profile analysis of a SnO₂/SiO₂/Si structure, modified with hexamethildisilazane and processed with rapid thermal annealing (RTA) in the temperature range of 800–1200 °C, is investigated in a hollow cathode discharge for the purpose of characterizing gas sensing solid state devices. The depth behavior of the elements tin, nitrogen, carbon and silicon in this structure is deduced from their emission spectra in the hollow cathode plasma. The hollow cathode used is a liquid nitrogen - cooled Al cylinder having 4 mm inner diameter and 12 mm length. Spectrally pure Ne at a pressure of 130 Pa is used as working gas. The hollow cathode discharge is supplied by a pulse generator with 10 μs pulse width, 4 kHz pulse frequency and 0.5 A pulse amplitude. The results are interpreted by possible reconstruction of hexamethyldisilazane molecule.     

Rapid analysis of polychlorinated biphenyls in the gas phase with resonance-enhanced two-photon ionization: optimal injection of ions into the ion-trap storage/time-of-flight mass spectrometer.

LI-IT-TOFMS (laser ionization/ion-trap storage/time-of-flight mass spectrometry) is expected to be a powerful tool for environmental monitoring. In the research reported here, real-time LI-IT-TOFMS measurements were carried out on gaseous 2-4 chlorinated PCBs in order to evaluate the applicability of an environmental monitoring method. With respect to ion-trap storage for PCBs, we found that the effect was due to the driving RF voltage on the ring electrode in the ion trap. For PCBs ions produced by laser irradiation, we observed that it was more efficient to reach the center of the ion trap by using a gated RF voltage rather than by using a continuous RF voltage. The ion trajectories in the ion trap were simulated by SIMION 7.0. We found that the voltage of the exit end cap electrode affected both the number of ions trapped and the orbit of ions inside the trap cell. Optimization of this parameter was performed using both simulated and experimental results. The achievable PCBs sensitivity for real-time (1 min) measurement using the LI-IT-TOFMS method was found to be in the pptV range (<0.01 mg/m3N) by means of a comparison with the conventional gas sampling/GS-MS method. A satisfactory proportional relationship was confirmed between the laser-based and conventional results.     

Analytical capabilities of the microwave-coupled hollow-cathode discharge in emission spectroscopy

The intensity of spectra emitted by hollow copper cathodes with and without the superposition of 2450-MHz microwaves was studied under different operating conditions with argon as the filler gas. The hollow-cathode discharge was operated at 25–200 mA, with argon pressures ranging from 166 to 690 Pa. The intensities of the copper spectral lines are usually higher in the presence of microwaves, whereas the argon lines are weaker. The differences in the copper spectral lines with and without microwaves increase with increasing pressure of the filler gas and decreasing current. Analogous conclusions were reached for aqueous solutions of gold and silver ions placed in the cathode cavity and dried prior to discharge. The suitability of the method for improving the detection limits obtainable with the hollow-cathode discharge could thus be demonstrated.