Design and performance of a plasma-source mass spectrograph

A plasma-source, simultaneously detecting, Mattauch-Herzog mass spectrograph for multi-element analysis was developed. Simultaneous detection should improve throughput, precision, and sensitivity over those instruments that use quadrupole or sector mass spectrometers. The new instrument is compact (approximately 80 cm in length) and is designed to detect a complete atomic mass spectrum in two mass windows that straddle but avoid argon. The design and some figures of merit are presented. With a dc glow discharge source, a precision of 0. 5% determined from eight consecutive 10-s images was obtained for Cu isotope ratios in Naval Brass B. With the same sample, nickel and lead were detected at limits of 8 and 1 ppm. Measured Mg isotope ratios with an inductively coupled plasma source were within 4% of the expected values. The resolution at full width at half maximum is currently limited to approximately 60, in part because of poor peak shape. The origin of this peak shape has been determined to lie within the array detector and possibly results from its interaction with the fringing magnetic fields produced by the second sector.     

Novel tandem quadrupole-acceleration-deceleration mass spectrometer for neutralization-reionization studies

A new tandem mass spectrometer of the quadrupole-acceleration lens-deceleration. lens-quadrupole (QADQ) configuration is described. The instrument is designed for neutralization-reionization studies and consists of a 2000-u quadrupole mass analyzer as MS-I, an acceleration electrostatic lens, a series of three differentially pumped collision cells, and an electrostatic deceleration lens, energy filter, and another 2000-u quadrupole mass analyzer as MS-II. The ion optical system achieves high total ion transmission for 5–9-keV ions. Unit mass resolution in neutralization-reionization mass spectra of aromatic compounds is demonstrated. Mass, kinetic energy, and linked scans at various levels of mass resolution and sensitivity are described.     

Simultaneous multichannel mass-specific detection for high-performance liquid chromatography using an array detector sector-field mass spectrometer

The use of a separation step, such as liquid chromatography, prior to inductively coupled plasma mass spectrometry (ICP–MS) has become a common tool for highly selective and sensitive analyses. This type of coupling has several benefits including the ability to perform speciation analysis or to remove isobaric interferences. Several limitations of conventional instruments result from the necessity to scan or pulse the mass spectrometer to obtain a complete mass spectrum. When the instrument is operated in such a non-continuous manner, duty cycle is reduced, resulting in poorer absolute limits of detection. Additionally, with scanning instruments, spectral skew can be introduced into the measurement, limiting quantitation accuracy. To address these shortcomings, a high-performance liquid chromatograph has been coupled to an ICP–MS capable of continuous sample introduction and simultaneous multimass detection. These features have been realized with a novel detector array, the focal plane camera. Instrument performance has been tested for both speciation analysis and for the elimination of isobaric interferences. Absolute limits of detection in the sub picogram to tens of picograms regime are obtainable, while the added mass dimension introduced by simultaneous detection dramatically increases chromatographic peak capacity.     

Fundamental and applied investigations in plasma-source mass spectrometry for elemental analysis

The current status of plasma source-mass spectrometry (PS-MS) is reviewed. An overview of interference effects that exist, alternative plasma sources available, and mass spectrometer interface studies is provided. A discussion of current and future development areas in plasma source mass spectrometry is also included.     

Novel ion mobility setup combined with collision cell and time-of-flight mass spectrometer

An ion mobility cell of a novel type was coupled to an orthogonal injection time-of-flight (TOF) mass spectrometer. The mobility cell operates at low-pressure and contains a segmented RF ion guide providing an axial electric field that drives the ions towards the exit. A flow of gas is arranged inside the ion guide in such a way that the gas drag counteracts the force exerted by the axial field. Ions with different mobility coefficients can be scanned out of the ion guide by ramping the axial field strength. The ions can be analyzed intact or fragmented in a collision cell before introduction into an orthogonal TOF mass spectrometer. An ion source with matrix assisted laser desorption/ionization (MALDI) was attached to the instrument. The setup was evaluated for the analysis of peptide and protein mixture, with sequential fragmentation of multiple precursor ions from a protein digest and with mobility separation of fragment ions formed by in-source fragmentation of pure peptides. The mobility resolution for peptides was observed to be three times higher than the theoretical resolution predicted for a classical mobility setup with similar operating conditions (pressure, field strength, and length).     

A multichannel electron energy loss spectrometer for low-temperature condensed films

We describe a wide-gap multichannel cylindrical deflection electron energy analyzer suitable for measuring the weak signals characteristic of electronically inelastic electron energy loss spectra. The analyzer has nearly ideal fringing field termination, and its resolution and energy dispersion were characterized as a function of energy by solving numerically the equation of motion of electrons in an ideal cylindrical electric field. The numerical results for the radial location of the electrons at the detector as a function of the entrance location, angle, and energy are closely approximated by a second order polynomial, and match closely with those observed. The detection efficiency of the analyzer is 100-150 times better than that of an equivalent single-channel instrument, but limited energy transmission of the zoom lens system used in our case reduced it by a factor of about 2. The performance of the new instrument was demonstrated by measuring the (3)E(1u) electronic spectrum of benzene in only 2 min and the spectrum of endo-benzotricyclo[4.2.1.0(2.5)]nonane.     

Sub-miniature ExB sector-field mass spectrometer

A novel sub-miniature double-focusing sector-field mass spectrometer has been fabricated at the University of Minnesota using a combination of conventional machining methods and thin film patterning techniques typically used in the sensor technology industry. Its design is based on the mass separation capabilities of a 90 degrees cylindrical crossed electric and magnetic sector-field analyzer with a 2-cm radius, which under proper conditions is able to effectively cancel the angular and chromatic dispersion of the ion beam, thus improving the resolving power of the instrument. Simulations using finite element analysis and computer modeling were employed to verify and optimize the performance of the proposed instrument before and during its fabrication. The prototype was able to attain a resolving power of 106 full-width at half-maximum (FWHM), a detection limit close to 10 parts per million, a dynamic range of 5 orders of magnitude and a mass range up to 103 Da. Its overall size, including the magnet assembly, is 3.5 cm wide, 6 cm long and 7.5 cm tall, it weighs 0.8 kg, and its power consumption was measured to be 2.5 W. The performance of the instrument was found to be comparable to that of commercial residual gas analyzers, at a fraction of the cost. All these characteristics make this miniature mass spectrometer suitable for portable and low-cost analytical instrumentation.     

Mass spectrometer with a multichannel ion detector based on microchannel plates

Position sensitive detectors based on microchannel plates were introduced in a mass spectrometer. With the help of this multichannel ion detector, the measurement time and errors are reduced significantly.     

Rapid multielemental analysis of Chinese reference soils by laser ablation inductively coupled plasma-source mass spectrometry

Summary Laser ablation inductively coupled plasma-source mass spectrometry has been used to determine thirty elements (Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, As, Rb, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Dy, Ho, Yb, Hf, Ta, W, Th, U) in seven Chinese reference soils. The Surrey prototype spectrometer was employed with sample ablation by a free-running ruby laser. Concentrations in the soils (GSS-2 to GSS-8) were calculated from elemental responses and sensitivities derived from another soil in the series, namely GSS-1. Comparisons with previous neutron activation analyses are made. Rapid semiquantitative analyses are proved feasible. About eighty percent of the LA-ICP-MS determined concentrations were within a factor of two of the concentrations measured by INAA, and many were considerably closer than this. Precisions were typically in the range 2–10% RSD, but some were considerably poorer for elements present at trace levels.     

X-ray imaging during plasma-source ion implantation

Plasma source ion implantation (PSII) is a technique for modifying stafaces that places the object to he modified directly into a plasma and then negatively pulse biases the object so as to implant positive ions. If the voltage is high enough, X-rays can he generated by electrons that are also accelerated by the pulse. This work describes techniques for imaging and characterizing the X-rays A pinhole camera was used to image the X-rays being emitted as electrons collided with surfaces in the chamber. The images show that X-rays are generated at the chamber walls and near the target. The time dependence of these X-rays during each pulse was examined using a PIN diode X-ray detector. Then, using another X-ray sensor and pulseheight analyzer, the spectra of the emitted X-rays was determined. The object is to relate the X-ray intensity and spectrum to the temporal and spatial values of the implantation dose so that it may he used as a process monitor and a control sensor.     

Evaluation of a differential mobility spectrometer/miniature mass spectrometer system

A planar differential mobility spectrometer (DMS) was coupled to a Mini 10 handheld rectilinear ion trap (RIT) mass spectrometer (MS) (total weight 10 kg), and the performance of the instrument was evaluated using illicit drug analysis. Coupling of DMS (which requires a continuous flow of drift gas) with a miniature MS (which operates best using sample introduction via a discontinuous atmospheric pressure interface, DAPI), was achieved with auxiliary pumping using a 5 L/min miniature diaphragm sample pump placed between the two devices. On-line ion mobility filtering showed to be advantageous in reducing the background chemical noise in the analysis of the psychotropic drug diazepam in urine using nanoelectrospray ionization. The combination of a miniature mass spectrometer with simple and rapid gas-phase ion separation by DMS allowed the characteristic fragmentation pattern of diazepam to be distinguished in a simple urine extract at lower limits of detection (50 ng/mL) than that achieved without DMS (200 ng/mL). The additional separation power of DMS facilitated the identification of two drugs of similar molecular weight, morphine (average MW = 285.34) and diazepam (average MW = 284.70), using a miniature mass spectrometer capable of unit resolution. The similarity in the proton affinities of these two compounds resulted in some cross-interference in the MS data due to facile ionization of the neutral form of the compound even when the ionic form had been separated by DMS.     

便携式质谱仪的研究进展

面对大气、河流、土壤等化学污染,各种突发性爆炸事故和化学泄漏事件,以及生化武器滥用等等社会问题,迫切需要对源头进行现场原位检测分析.质谱(MS)以其检测速度快、灵敏度高、检测样品量少、可对未知物定性定量检测等特点,非常适合应用于这些现场的分析检测.然而实验室用MS的体积、重量、功耗等较大,不便于搬运,无法实现现场的原位...     

Recent trends in mass spectrometer development

Trends in mass analyzer development are reviewed here with an emphasis on tandem mass spectrometers. The move toward hybridization of conventional mass analyzers to allow additional instrument functionality in tandem mass spectrometry is discussed.     

A Quadrupole mass spectrometer for resolution of low mass isotopes

The qualitative and quantitative identification of low mass isotopes in the mass range 1–6 u poses certain difficulties when attempting to achieve the required resolution with an instrument suitable for deployment within a process environment. Certain adjacent species present in the process sample (HT and D₂) require a resolution greater than 930 to achieve an accurate measurement. We demonstrate here through simulation techniques that this level of performance required is unachievable using commercially available instruments. Using previously reported simulation techniques, this article demonstrates how the required performance for resolving the low mass isotopes can be achieved by a quadrupole mass spectrometer (QMS), which incorporates a quadrupole mass filter (QMF) constructed from hyperbolic electrodes and operated in zone 3 of the Mathieu stability diagram.     

An electrospray-ionization mass spectrometer with new features

The construction and performance of an electrospray-ionization mass spectrometer with new features are described. The mass spectrometer consists of a newly designed electrospray ion-source that is plugged directly into a modified commercial quadrupole mass spectrometer with the ions entering the mass analyzer through a long metal capillary tube and three stages of differential pumping. The present ion source differs from previous designs in the combination of techniques employed in the transportation and desolvation of solvated biomolecule ions, prior to mass analysis. Transport of ionized entities between atmospheric pressure and vacuum is carried out through a 203 mm long stainless steel capillary tube with a 0.5 mm bore. Desolvation is effected by the use of controlled heat transfer through the long capillary tube and collisional activation in a region of reduced pressure between the capillary tube exit and the skimmer. Desolvation with this system is convenient and effective and does not involve the strong countercurrent flows of gases that have been used by all previous workers. The effects on the spectra of peptides of capillary tube temperature and desolvation collision energy are investigated. Electrospray-ionization mass spectrometric results are described for thirteen proteins with molecular masses ranging from 5000 to 77,000 Da. The performance of the present instrument, with respect to mass accuracy and sensitivity, is comparable with previously reported systems. The effect of protein concentration in solution on the electrospray mass spectrometric response and charge-state distribution is discussed.     

A constant-momentum/energy-selector time-of-flight mass spectrometer

A matrix assisted laser desorption/ionization time-of-flight mass spectrometer has been built with an ion source that can be operated in either constant-energy or constant-momentum acceleration modes. A decreasing electric field distribution in the ion-accelerating region makes it possible to direct ions onto a space-focal plane in either modes of operation. Ions produced in the constant-momentum mode have velocities and, thus, flight times that are linearly dependent on mass and kinetic energies that are inversely dependent on mass. The linear mass dispersion doubles mass resolving power of ions accelerated with space-focusing conditions in constant-momentum mode. The mass-dependent kinetic energy is exploited to disperse ions according to mass in a simple kinetic energy filter constructed from two closely spaced, oblique ion reflectors. Focusing velocity of ions of the same mass can substantially improve ion selection for subsequent post source decay or tandem time-of-flight analyses.