Stage Mass Spectrometer Research Articles

A 2.45 GHz microwave ion source for carbon positive-ion mass spectrometry

Carbon positive-ion mass spectrometry (C-PIMS) is a two stage mass spectrometer by producing high charge state carbon ions (C2+/C3+) directly in the ion source to eliminate molecular interferences and by converting the beam (C2+/C3+) to C− ions in a charge exchange cell to eliminate 14N interference. It has been proven that C-PIMS is an effective method for the detection of radiocarbon at low levels. This article will focus on the multiply charged carbon ion generation. Based on the fact that a C-PIMS system is usually equipped with high frequency electron cyclotron resonance (ECR) ion sources. It is significant to investigate if the simple and low-cost 2.45 GHz ECR ion source is an optional choice for the C-PIMS. At Peking University (PKU), a 2.45 GHz microwave ion source with minimum-B magnetic field configuration is designed for the production of intense C2+ beam. Preliminary experiments have proved that the 2.45 GHz microwave ion source can produce up to 40 μA@40 keV C2+ beam. In addition, it was found that argon could increase the decomposition efficiency of CO2, which can eliminate CO2+ ions of the extracted beam.

Development of Thermal Dissociation Atmospheric Chemical Ionization Source for Rapid Mass Spectrometry Analysis of Ambient Samples

A thermal dissociation atmospheric chemical ionization (TDCI) source was developed for the rapid chemical ionization of ambient analytes in complex matrices. The performance of TDCI has been experimentally explored by coupling the TDCI source to a commercial LTQ XL mass spectrometer, and the dissociation of chemical reagents, for example ionic liquids, has been systematically investigated using multiple stage mass spectrometer. The primary ions, generated through the thermal dissociation process of the ionic liquids, were accelerated by the bias voltage applied to the repelling electrode of the TDCI source, then reacted with the analytes present in the matrices of the raw samples to produce analyte ions. The analyte ions were finally guided into the LTQ instrument for mass analysis. The construction of the TDCI source was detailed in the text. The effects of the experimental parameters such as the temperature, the distance, and the angles formed between the electrodes were experimentally studied using the signals of characteristic fragments of the ionic liquid. Under the optimal experimental conditions, TDCI was able to directly ionize a wide variety of compounds, including the poplar (e.g., amino acids, doping compounds) and nonpolar chemicals (e.g., naphthalene), for sensitive detection using LTQ-MS, without any sample pretreatment. The average time for a single sample analysis was less than 30 s, the relative standard deviation of the method was in the range of 5.89%–11.1%, and the limit of detection (LOD) for naphthalene was estimated to be 2.9 × 10−7 g L−1.

Enhanced Direct Ambient Analysis by Differential Mobility-Filtered Desorption Electrospray Ionization-Mass Spectrometry

Desorption electrospray ionization (DESI) is rapidly becoming established as one of the most powerful ionization techniques allowing direct surface analysis by mass spectrometry (MS) in the ambient environment. DESI provides a significant number of unique analytical capabilities for a broad range of applications, both quantitative and qualitative in nature including biological tissue imaging, pharmaceutical quality control, in vivo analysis, proteomics, metabolomics, forensics, and explosives detection. Despite its growing adoption as a powerful high throughput analysis tool, DESI-MS analysis at trace levels often suffers from background chemical interferences generated during the electrospray ionization processes. In order to improve sensitivity and selectivity, a differential mobility (DM) ion separation cell was successfully interfaced to a custom-built DESI ion source. This new hybrid platform can be operated in two modes: the "DM-off" mode for standard DESI analysis and "DM-on mode" where DESI-generated ions are detected after discrimination by the differential mobility cell. The performance of the DESI-DM-MS platform was tested with several samples typically amenable to DESI analysis, including counterfeit pharmaceuticals and binary mixtures of isobaric chemicals of importance in the pharmaceutical and food industries. In the DM-on mode, DESI-MS signal-to-noise ratios were improved by 70-190% when compared to the DM-off mode. Also, the addition of the DM cell enabled selective in-source ion activation of specific DESI-generated precursor ions, providing tandem MS-like spectra in a single stage mass spectrometer.

Radiocarbon detection by ion charge exchange mass spectrometry

A method for detection of radiocarbon at low levels is described and the results of tests are presented. We refer to this method as ion charge exchange mass spectrometry (ICE-MS). The ICE-MS instrument is a two stage mass spectrometer. In the first stage, molecular interferences which would otherwise affect radiocarbon detection at mass 14 are eliminated by producing high charge state ions directly in the ion source (charge state ⩾2). 14N interference is eliminated in the second stage by converting the beam to negative ions in a charge exchange cell. The beam is mass-analysed at each stage. We have built a test apparatus consisting of an electron cyclotron resonance ion source and a pair of analysing magnets with a charge exchange cell in between, followed by an electrostatic analyser to improve the signal to background ratio. With this apparatus we have measured charge exchange probabilities for (Cn+→C−) from 4.5 to 40.5keV (n=1–3). We have studied the sources of background including assessment of limits for nitrogen interference by searching for negative ions from charge exchange of 14N ions. Our system has been used to detect 14C in enriched samples of CO2 gas with 14C/12C isotopic ratio down to the 10−9 level. Combined with a measured sample consumption rate of 4ng/s, this corresponds to a capability to detect transient signals containing only a few μBq of 14C activity, such as may be obtained from chromatographic separation. The method will require further development to match the sensitivity of AMS with a gas ion source; however, even in its present state its sensitivity is well suited to tracer studies in biomedical research and drug development.

Quadrupole ion trap mass spectrometry

The quadrupole ion trap (QIT) is constructed of three electrodes that, when held at appropriate potentials, cause the formation of a trapping pseudo-potential well so that charged particles, or gaseous ions, may be confined or stored for long periods of time. The two end-cap electrodes resemble saucers while the ring electrode resembles a napkin ring; all of the electrodes are of hyperbolic geometry. The ion trap itself functions as a mass spectrometer when the ion-confining conditions are modified such that ions are ejected mass-selectively from the trapping potential well. As ions of successive mass/charge ratios are ejected in turn from the ion trap, they impinge upon an external detector whereby ion signals are created in proportion to the ion number of each species; in this manner, a mass spectrum is generated. The QITMS (quadrupole ion trap mass spectrometer) is an extraordinary instrument in that it is physically small (the entire electrode assembly can be held in the palm of one's hand) compared with magnetic and electric sector instruments, it is relatively inexpensive, it is one of the most, if not the most, sensitive mass spectrometers and, since several mass-selective operations can be carried in succession, the ion trap can function as a tandem mass spectrometer. Tandem mass spectrometric operation is described as (MS)n. With the QITMS, (MS)n is carried out in time in the same volume of space whereas (MS)n in sector instruments is carried out in space. With sector instruments, the maximum value of n is n = 4 yet with the ion trap, (MS)n where n = 4–6 can be carried out routinely and n = 13 has been achieved. The QITMS shares several similarities with the ion cyclotron resonance mass spectrometer yet the cost of the former is about one-tenth that of the latter. One striking difference between the QITMS and all other mass spectrometers is that the QITMS operates at a pressure of 10−3 Torr compared with 10−6 to 10−9 Torr for other mass spectrometers. The theory of ion confinement and ion trajectory manipulation in the QITMS has been explained relatively simply so far. Since the theory differs widely from those of sector instruments and ion cyclotron resonance mass spectrometry (ICR/MS), it will not be familiar to those who have not had the opportunity to examine ion motion in quadrupole fields. Optimum operation of the QITMS is effected by collisional focusing of the ion cloud to the center of the ion trap under the influence of helium buffer gas. Since the movement of ions confined in the ion trap is periodic, the trajectories of collisionally focused ions can be expanded by resonance excitation effected by the imposition of supplementary radio frequency (rf) potentials of low amplitude to the end-cap electrodes of the ion trap. This excitation operation permits isolation of selected ion species, by ejection of unwanted ion species, followed by selective ion/molecule reaction or by collision-induced dissociation (CID) with subsequent mass analysis of the product/fragment ions formed. Sample calculations are given of all of the relevant trapping parameters. Applications of the QITMS as a single stage mass spectrometer and as a tandem mass spectrometer are discussed. The operation of the QITMS for the identification of dioxins and furans co-eluting from a gas chromatograph is described. In addition, the application of chemical ionization (CI) for the identification of co-eluting polychlorinated biphenyl (PCB) congeners is discussed. The QITMS is an extraordinary instrument that is capable of great sensitivity, high mass range and high mass resolution. Since the QITMS is compatible with methods for generating ions externally, such as electrospray ionization (ESI), its continued growth in many areas of mass spectrometry (MS) is assured. The structural details of the glycoprotein and the optical spectroscopy of stored ions are applications of the QITMS combined with ESI, while the ion trap in combination with a metal-cluster aggregation source has been used for an electron diffraction study.

Quantification and confirmation of identity of analytes in various matrices with in-source collision-induced dissociation on a single quadrupole mass spectrometer

Mass spectrometry is often used for the quantification of target analytes. When liquid chromatography (LC) is interfaced with mass spectrometry, it is generally accepted that tandem mass spectral (MS/MS) techniques are required to quantify an analyte with confirmation of identity in a complex matrix. In such applications LC is generally used to deliver the sample to the mass spectrometer with minimal separation, and the bulk of the separation is downloaded to the tandem mass spectrometer. However, LC is also a powerful separations tool, and a tandem mass spectrometer is not required to gain fragmentation data. In-source collision-induced dissociation (IS-CID) on a single stage mass spectrometer will generate rich fragmentation patterns that are often used for qualitative identification and rarely for quantitative confirmation of identity. Quantification with confirmation of identity on a single stage quadrupole mass spectrometer can be done by concurrently monitoring for the expected parent and fragment ions using multiple selected ion recording (SIR) channels. Although such methods have been used to quantify analytes with confirmation of identity in simple matrices, only isolated examples of such work with complex matrices are published. We will extend upon the previous work and discuss the utility of using single quadrupole mass spectrometers for the quantification of an analyte with concurrent confirmation of identity in complex matrices. The analysis of methomyl in spinach extract demonstrates the ability of simple LC/MS to separate out interferences and give accurate relative abundances of fragments. Sulfometuron methyl was quantified accurately out of apple matrix at a level of 200 pg/μL, even with a calibration curve run in pure solvents. β-Lactam antibiotics and lincomycin were analyzed out of bovine milk extract. The limits of detection (LOD) for the β-lactam antibiotics ranged from 15.5 to 105 pg of material on-column, and although these LODs were higher than observed with a triple quadrupole mass spectrometer, they were actually superior to those observed on an ion trap mass spectrometer. Lincomycin gave an LOD of 0.83 pg on-column, despite the fact that trifluoroacetic acid (TFA) was required to give adequate chromatography. In our final example, we demonstrate the quantification of ritonavir out of blood plasma extract. The LOD of ritonavir under these conditions was 2.2 pg on-column. For both lincomycin and ritonavir we achieve confirmation of identity even at the lowest concentrations we ran.

A mass spectrometric method for studying charge transfer reactions

A modified single stage mass spectrometer for studying charge transfer reactions is described. The energies of the ionizing electrons and of the primary ions can be controlled independently. The electron energy (range: 10–70 eV) has a spread of less than 1 eV and that of the primary ions (range: 20–150 eV) less than 2 eV. The apparatus can measure simultaneously the primary and secondary ion currents. The cross sections obtained are in agreement with those obtained with single and tandem mass spectrometers. The apparatus was used for determinations of cross sections and break-down spectra as functions of the energies of the primary ions or of the ionizing electrons.

Specific Features of Tohoku Charge Spectrometer

This report describes the specific features of the Tohoku Charge Spectrometer(TOHOKU CS)which has been constructed for the study of chemical effects of the nuclear transformations in gases, especially of the charge distribution of the residual atoms and of ion-molecule reactions in order to elucidate the primary and elemental stages in hot-atom chemistry. The facility is available for a chargespectrometer with a large source volume and a double mass spectrometer connected in perpendicular. Ions can be produced by the electron impact, X-ray irradiation or nuclear decay processes in the source volume. Charge spectrum of the residual atom after the Auger process of the nuclear decay can be measured through the first stage mass spectrometer, and products of ion-molecule reactions in the reaction chamber can be separated through the second mass spectrometer and detected by an aid of a16stages Cu-Be electron multiplier. Pulse countings are applicable in the both cases as well as direct current recordings to estimate the charged atoms or the fragment distribution. The specific availabilities of this facility are shown in some typical results by the preliminary experiments.

A two stage mass spectrometer for nuclear physics applications, part II

This paper describes the main electronics features of a double magnetic stage mass spectrometer described previously. Particular emphasis is given to the details of the high stability accelerating voltage scanning and magnet supplies, the mass switching and the ion counting equipment.

A two stage mass spectrometer for nuclear physics applications

The design of the mass spectrometer described in this paper makes it very useful in a number of nuclear physics applications. Two 90° magnetic stages, each of 15″ radius, are used together with an accelerating voltage of 15kV. Scanning is by variation of the accelerating potential, the magnetic fields being held constant to one part in 10 5 by nuclear magnetic resonance. Organic materials are excluded with consequent reduction in “hydrocarbon” background. The design of the spectrometer is described and the performance discussed. A later paper will describe the electronic side of the machine.

A Three Stage Mass Spectrometer

A three stage mass spectrometer, utilizing two consecutive magnetic focusing lenses of 20″ radii followed by a 20” radius of curvature electrostatic analyzer, is described An abundance sensitivity of 1010 was measured for this instrument in the low mass region. Application of this instrument to analytical and research problems in the field of mass spectrometry and results obtained are discussed.