Ion Trap Mass Spectrometer Research Articles

Tailored ion beam for precise colour centre creation.

We present an invariant-based quantum control scheme leading to a highly monochromatic ion beam from a Paul trap. Our protocol is implementable by supplying the segmented electrodes in the trap with voltages of the order of volts. This mitigates the impact of fluctuations in previous designs and leads to a low-dispersion beam of ions. Moreover, our proposal does not rely on sympathetically cooling ions, which bypasses the need of loading different species in the trap-namely, the propelled ion and, e.g. a [Formula: see text] to exert sympathetic cooling-significantly incrementing the repetition rate of the launching procedure. Our scheme is based on an invariant operator linear in position and momentum, which enables us to control the average extraction energy and the outgoing momentum spread. In addition, we propose a sequential operation to tailor the transversal properties of the beam before the ejection to minimize the impact spot and to increase the lateral resolution of the implantation. This article is part of the theme issue 'Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives'.

Development of low power and high voltage RF signal generator

Ion confinement technology can be widely used in quantum computation and precision measurement. In ion trapping system, ions are stably trapped in ion trap by the action of external forces.Multi-ion confinement requires the joint action of electric field and magnetic field to make the trapped ions overcome the interaction force between ions and be stably confined in the same specific space. Therefore, the stability of the electric force and the magnetic force determines the stability of ion confinement. Although the electric field and magnetic field provided by traditional commercial instruments is stable, it is not conducive to the miniaturization of the device. According to the previous experiment of ion confinement, we have designed a radio frequency(RF) signal generator that can provide continuous low power and stable high voltage RF electric field for multi-ion confinement system to guarantee the stability of trapped ions in quadrupole linear ion trap, also to improve the tapped ions density.

Photoelectron imaging of cryogenically cooled BiO- and BiO2 - anions.

The advent of ion traps as cooling devices has revolutionized ion spectroscopy as it is now possible to efficiently cool ions vibrationally and rotationally to levels where truly high-resolution experiments are now feasible. Here, we report the first results of a new experimental apparatus that couples a cryogenic 3D Paul trap with a laser vaporization cluster source for high-resolution photoelectron imaging of cold cluster anions. We have demonstrated the ability of the new apparatus to efficiently cool BiO- and BiO2 - to minimize vibrational hot bands and allow high-resolution photoelectron images to be obtained. The electron affinities of BiO and BiO2 are measured accurately for the first time to be 1.492(1) and 3.281(1) eV, respectively. Vibrational frequencies for the ground states of BiO and BiO2, as well as those for the anions determined from temperature-dependent studies, are reported.

Resolved-sideband micromotion sensing in Yb+ on the 935 nm repump transition

Ions displaced from the potential minimum in an RF Paul trap exhibit excess micromotion. A host of well-established techniques are routinely used to sense (and null) this excessive motion in applications ranging from quantum computing to atomic clocks. The rich atomic structure of Yb+, a heavy ion, includes low-lying 2D3/2 states that must be repumped to permit Doppler cooling, typically using a 935 nm laser coupled to the 3D[3/2]1/2 states. In this article, we demonstrate the use of this transition to make resolved-sideband measurements of 3D micromotion in 172Yb+ and 171Yb+ ions. Relative to other sensing techniques, our approach has very low technical overhead and is distinctively compatible with surface-electrode ion traps.

Comparative pharmacokinetic study of nine bioactive components in osteoarthritis rat plasma using ultra-performance liquid chromatography-tandem mass spectrometry after single and combined oral administration of Epimedii Folium and Chuanxiong Rhizoma extracts.

The herb pair Epimedii Folium-Chuanxiong Rhizoma (EF-CR), derived from the classical traditional Chinese medicine 'Xian Ling Pi San', has a distinctive compatibility therapeutic profile and is clinically safe and effective. This study aimed to investigate and compare the pharmacokinetic characteristics of nine analytes in osteoarthritis (OA) rat plasma after the oral administration of EF, CR or a combination of these two herbs. We developed an ultra-performance liquid chromatography method coupled with quadrupole linear ion-trap mass spectrometry to simultaneously quantify and assess the pharmacokinetics of icariin, epimedin A, epimedin B, epimedin C, icariside I, icariside II, ferulic acid, ligustilide and senkyunolide A of the EF-CR pair in the plasma of osteoarthritic rats. The pharmacokinetic parameters showed that the absorption of multiple components was significantly enhanced and residence time was prolonged in the EF-CR group (P < 0.05) compared to the single-herb group. These parameters revealed that the combination of EF and CR exhibited synergistic effects of the nine bioactive components, suggesting the potential application of the EF-CR combination for the treatment of OA.

All Ion Fragmentation Analysis Enhances the Untargeted Profiling of Glucosinolates in Brassica Microgreens by Liquid Chromatography and High-Resolution Mass Spectrometry.

An analytical approach based on reversed-phase liquid chromatography coupled to electrospray ionization Fourier-transform mass spectrometry in negative ion mode (RPLC-ESI-(-)-FTMS) was developed for the untargeted characterization of glucosinolates (GSL) in the polar extracts of four Brassica microgreen crops, namely, garden cress, rapeseed, kale, and broccoli raab. Specifically, the all ion fragmentation (AIF) operation mode enabled by a quadrupole-Orbitrap mass spectrometer, i.e., the systematic fragmentation of all ions generated in the electrospray source, followed by the acquisition of an FTMS spectrum, was exploited. First, the best qualifying product ions for GSL were recognized from higher-energy collisional dissociation (HCD)-FTMS2 spectra of representative standard GSL. Extracted ion chromatograms (EIC) were subsequently obtained for those ions from RPLC-ESI(-)-AIF-FTMS data referred to microgreen extracts, by plotting the intensity of their signals as a function of retention time. The alignment of peaks detected in the EIC traces was finally exploited for the recognition of peaks potentially related to GSL, with the EIC obtained for the sulfate radical anion [SO4]•- (exact m/z 95.9523) providing the highest selectivity. Each putative GSL was subsequently characterized by HCD-FTMS2 analyses and by collisionally induced dissociation (CID) multistage MSn (n = 2, 3) acquisitions based on a linear ion trap mass spectrometer. As a result, up to 27 different GSLs were identified in the four Brassica microgreens. The general method described in this work appears as a promising approach for the study of GSL, known and novel, in plant extracts.

Development of a liquid chromatography-tandem mass spectrometry method for the analysis of docetaxel-loaded Poly(lactic-co-glycolic acid) nanoparticles

Docetaxel is among the most effective chemotherapeutic agents used for the treatment of solid tumors, such as breast cancer. Targeting docetaxel to the tumor site would increase the safety and efficacy of the treatment. The focus of this work was to develop an efficient liquid chromatography tandem mass spectrometry (LC-MS/MS) method to quantify docetaxel entrapped in optimized poly lactic-co-glycolic acid (PLGA) nanoparticles. Several nanoparticle formulations were prepared to optimize the nanoparticles based on their size and yield percentage using a modified solvent evaporation technique. The MS/MS fingerprints of docetaxel and paclitaxel (as internal standard) were used to identify diagnostic product ion for developing a multiple reaction monitoring (MRM) LC-MS/MS method for the quantification of docetaxel in the PLGA nanoparticles. A triple quadrupole linear ion trap instrument (AB Sciex 4000 QTRAP) equipped with electrospray ionization was used. The optimized nanoparticles had a zeta potential of −23.2 ± 1.4 mV and mean particle sizes of 202.2 ± 4.7 nm and 251.7 ± 8.2 nm before and after freeze-drying, respectively. Polydispersity index values of the nanoparticles confirmed their uniform size distribution. The developed LC-MS/MS method could quantify docetaxel in the PLGA matrix with accuracy and precision covering a broad linear range of 15.6–4000 ng/mL. Method validation was conducted using the regulatory guidelines of the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) and showed acceptable values for all the tested criteria. The developed LC-MS/MS method with the novelty of using a phenyl column will be beneficial for future analysis of docetaxel loaded polymeric nano-delivery systems.

Observation of Undercooling in a Levitated Nanoscale Liquid Au Droplet

We investigate melting and undercooling in nanoscale (radius ∼100 nm) gold particles that are levitated in a quadrupole ion (Paul) trap in a high vacuum environment. The particle is heated via laser illumination and probed using two main methods. First, measurements of its mass are used to determine the evaporation rate during illumination and infer the temperature of the particle. Second, direct optical measurements show that the light scattered from the particle is significantly different in its liquid and solid phases. The particle is repeatedly heated across its melting transition, and the dependence of heating behavior on particle size is investigated. Undercooling─the persistence of a liquid state below the melting temperature─is induced via multistage laser pulses. The extent of undercooling is explored and compared to theoretical predictions.

Development and application of a miniature mass spectrometer with continuous sub-atmospheric pressure interface and integrated ionization source

For the miniature mass spectrometer (MS) with a continuous atmospheric pressure interface (CAPI), the gas in the multi-stage chambers directly affects the performance of the instrument. In this study, a sealed ionization chamber is designed to couple with a conventional mini CAPI-MS. In this configuration, the gas environment in the first ionization chamber can be flexibly changed to regulate the gas conditions throughout the entire instrument. By studying the effect of gas pressure on the performance of the instrument, we found that the instrument shows some unique advantages when the first ionization chamber is under sub-atmospheric pressure (SAP) conditions, such as reducing the load of the vacuum pump by 40%, achieving pump-free injection for gas and liquid samples, and improving the resolution by a factor of 2 without loss of detection sensitivity. Therefore, we propose a new integrated interface called continuous sub-atmospheric pressure interface (CSAPI) for building a miniature ion trap mass spectrometer. The CSAPI specially integrates sample introduction, gas/ions interface, and ionizations, including electrospray ionization (ESI) and secondary electrospray ionization (SESI), making this system more convenient for non-professional handlers to rapidly identify or monitor target analytes in gaseous- and solution-phase samples. We also use this system to study gas composition to further improve performance, being able to achieve a 5-fold sensitivity and 2-fold resolution improvement. At last, some custom applications of the current CSAPI-MS platform are explored and demonstrated, including real-time monitoring of chemical reactions in solution and long-distance sampling and analysis of dried Chinese herbs. In conclusion, this study provides a new approach to constructing a complete, versatile and practical miniature MS instrument.

Metabolic profiling and pharmacokinetic studies of Baihu-Guizhi decoction in rats by UFLC-Q-TOF–MS/MS and UHPLC-Q-TRAP-MS/MS

BackgroundBaihu-Guizhi decoction (BHGZD) is a well-documented traditional Chinese Medicine (TCM) prescription that has been extensively applied to treating rheumatoid arthritis. Despite of its beneficial outcomes, the chemical constituents of BHGZD have not been fully portrayed and the in vivo absorption, distribution, metabolism, and excretion (ADME) patterns of absorbed components have never been described.MethodsCharacterization of absorbed components and in vivo biotransformation profiling of these feature compounds were based on the ultra-fast liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry (UFLC-Q-TOF-MS/MS). Furthermore, the ultra-high-performance liquid chromatography tandem ion trap quadrupole mass spectrometry (UHPLC-Q-TRAP-MS/MS) system were performed to investigate the pharmacokinetics of active ingredients from BHGZD.ResultsIn this study, we have identified and tentatively characterized 18 feature absorbed prototype and 15 metabolites of BHGZD in rat serum and the in vivo transformation pathways of these absorbed constituents were proposed. Besides, we have established novel quantitative methodology of five crucial components of BHGZD and have monitored the pharmacokinetic behaviors of these constituents spontaneously in rat serum after BHGZD gavage. After rats received two ways of BHGZD gavage, the pharmacokinetic behaviors of each compound exhibited relatively similar behaviors, as evidenced by similar curve track as well as relatively close time to reach maximum concentration (Tmax) and half washout time (T1/2). Whereas the maximum plasma concentration (Cmax) and area under the plasma concentration–time curve (AUC) values of five analytes with multiple dosage were a bit higher than single dosage.ConclusionThis study added knowledge into the material basis and bio-transformation patterns of BHGZD in vivo, which would be of great value for exploring pharmacological effects and mechanism of BHGZD.

Coherent control of a local phonon in trapped ions using dynamical decoupling

In this paper, we present a dynamical decoupling (DD) technique to coherently control the dynamics of a single local phonon in trapped ions. A 2$\pi$ rotation at a motional sideband transition flips the sign of the relevant local phonon state, resulting in cancellation of the phonon dynamics. In this work, we implement DD using single and multiple blue-sideband pulses to control a single local phonon in two $^{40}{\rm Ca}^{+}$ ions in a linear Paul trap. Our proposed DD technique can be used to engineer coupling between local phonon modes.

Feasibility study on ground-state cooling and single-phonon readout of trapped electrons using hybrid quantum systems

Qubits of long coherence time and fast quantum operations are long-sought objectives toward the realization of high-fidelity quantum operations and their applications to quantum technologies. An electron levitated in a vacuum by a Paul trap is expected to be a good candidate, for its light mass and hence the high secular frequency which allows for faster gate operations than those in trapped ions. Controlling the motional state of the trapped electron is a crucial issue, for it mediates an interaction between electron spins, intrinsic qubits embedded in electrons, and its decoherence results in degraded fidelity of two-qubit gates. In addition, an efficient readout of the motional state is important, regarding the possibility of detecting spin state by using it. Despite such importance, how to achieve the motional ground state and how to efficiently detect it are not reported so far. Here we propose methods addressing these issues by utilizing hybrid quantum systems involving an electron-superconducting circuit and electron-ion coupled systems and analyze the feasibility of our schemes. In both systems, we show that ground-state cooling and single-phonon readout of the motional state of the trapped electron are possible. Our work sheds light on a way to precisely control the motional states of the trapped electrons, that provides an interesting playground for the development of quantum technologies.

Second-order Doppler frequency shifts of trapped ions in a linear Paul trap

The accurate evaluation of the second-order Doppler frequency shift (SODFS) of trapped ions in a linear Paul trap has been studied with experiments and molecular dynamics (MD) simulations. The motion of trapped ions in the trap has three contributions, and we focus on the ion excess micromotion, which is rarely discussed when evaluating the SODFS. Based on the hypothesis that the ion density is uniformly distributed in the radial direction, we propose a new model to accurately evaluate the total SODFS for ion microwave clocks. The effectiveness of the model has been verified both in simulation and experiment, especially for ion ensemble with temperature less than 100 mK. We believe that our new model offers advantages in accurately evaluating the SODFS for the ion trap, especially those of laser-cooled ion microwave clocks based on large ion clouds.

High-accuracy determination of Paul-trap stability parameters for electric-quadrupole-shift prediction

The motion of an ion in a radiofrequency (rf) Paul trap is described by the Mathieu equation and the associated stability parameters that are proportional to the rf and dc electric field gradients. Here, a higher-order, iterative method to accurately solve the stability parameters from measured secular frequencies is presented. It is then used to characterize an endcap trap by showing that the trap’s radial asymmetry is dominated by the dc field gradients and by measuring the relation between the applied voltages and the gradients. The results are shown to be in good agreement with an electrostatic finite-element-method simulation of the trap. Furthermore, a method to determine the direction of the radial trap axes using a “tickler” voltage is presented, and the temperature dependence of the rf voltage is discussed. As an application for optical ion clocks, the method is used to predict and minimize the electric quadrupole shift (EQS) using the applied dc voltages. Finally, a lower limit of 1070 for the cancellation factor of the Zeeman-averaging EQS cancellation method is determined in an interleaved low-/high-EQS clock measurement. This reduces the EQS uncertainty of our 88Sr+ optical clock to ≲1×10−19 in fractional frequency units.

A Diagnostic Nitrosamine Detection Approach for Pharmaceuticals by Using Tandem Mass Spectrometry Based on Diagnostic Gas-Phase Ion-Molecule Reactions.

N-Nitrosamines are strictly regulated in pharmaceutical products due to their carcinogenic nature. Therefore, the ability to rapidly and reliably identify the N-nitroso functionality is urgently needed. Unfortunately, not all ionized N-nitroso compounds produce diagnostic fragment ions and hence tandem mass spectrometry based on collision-activated dissociation (CAD) cannot be used to consistently identify the N-nitroso functionality. Therefore, a more reliable method was developed based on diagnostic functional-group selective ion-molecule reactions in a linear quadrupole ion trap mass spectrometer. 2-Methoxypropene (MOP) was identified as a reagent that reacts with protonated N-nitrosamines in a diagnostic manner by forming an adduct followed by the elimination of 2-propenol (CH3C(OH)═CH2]). From 18 protonated N-nitrosamine model compounds studied, 15 formed the diagnostic product ion. The lack of the diagnostic reaction for three of the N-nitrosamine model compounds was rationalized based on the presence of a pyridine ring that gets preferentially protonated instead of the N-nitroso functionality. These N-nitrosamines can be identified by subjecting a stable adduct formed upon ion-molecule reactions with MOP to CAD. Further, the ability to use ion-molecule reactions followed by CAD to differentiate protonated O-nitroso compounds with a pyridine ring from analogous N-nitrosamines was demonstrated This methodology is considered to be robust for the identification of the N-nitroso functionality in unknown analytes. Lastly, HPLC/MS2 experiments were performed to determine the detection limit for five FDA regulated N-nitrosamines.

Simultaneous determination of the residues of anesthetics and sedatives in fish using LC-QLIT-MS/MS combined with DSPE

Liquid chromatography coupled with quadrupole linear ion trap tandem mass spectrometry (LC-QLIT-MS/MS) technology operated in electrospray ionization (ESI) was developed for tracing anesthetic (AETs) and sedatives (SDTs) in fish. Sampling procedure was achieved by using acetonitrile extraction followed by dispersive solid phase extraction (DSPE) clean-up. Under the optimized laboratory conditions, reliable qualitative confirmation was obtained through the multiple reaction monitoring-information dependent acquisition-enhanced product ion (MRM-IDA-EPI) mode. Results indicated a favorable linear in the concentration range of 1–100 μg∙kg−1 (0.1–10 μg∙kg−1 for MS-222), with regression coefficient not less than 0.9997. The detection limit ranges from 0.03 to 0.4 μg∙kg−1 (S/N = 3). The validated method was applied to determine AETs and SDTs in fish with satidfied recoveries of 86.3 %–111.7 % and the relative standard deviations (RSD) of 1.9 %–8.9 % (n = 6). Practical samples analysis indicated that the proposed method is simple, rapid, sensitive and accurate for identification of AETs and SDTs.

Proton Affinities of Alkanes.

Chemical characterization of complex mixtures of large alkanes is critically important for many fields, including petroleomics and the development of renewable transportation fuels. Tandem mass spectrometry is the only analytical method that can be used to characterize such mixtures at the molecular level. Many ionization methods used in mass spectrometry involve proton transfer to the analyte. Unfortunately, very few proton affinity (PA) values are available for alkanes. Indeed, previous research has shown that most protonated alkanes (MH+) are not stable but fragment spontaneously via the elimination of a hydrogen molecule to form [M - H]+ ions. Here, the PAs of several n-alkanes and alkylcyclohexanes containing 5-8 carbon atoms, n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane, and ethylcyclohexane, were determined via bracketing experiments by using a linear quadrupole ion trap mass spectrometer. Monitoring the formation of the [M - H]+ ions in reactions between the alkanes and protonated reference bases with known PAs revealed that the PAs of all the alkanes fell into the range 721 ± 20 kJ mol-1. In order to obtain a more accurate estimate of the relative PAs of different alkanes, two alkanes were introduced simultaneously into the ion trap and allowed to react with the same protonated reference base. Based on these experiments, the longer the alkyl chain in an n-alkane or alkylcyclohexane the greater the PA. Further, when considering alkanes with the same number of carbon atoms, the PAs of those with a cyclohexane ring were found to be greater than those with no such ring.

Understanding the effect of spatial positioning of coated blade spray devices relative to the mass spectrometry inlet on different instrument platforms and its application to quantitative analysis of fentanyl and related analogs.

We evaluated the effect that the spatial positioning of coated-blade spray (CBS) devices with respect to the mass spectrometry (MS) inlet has when coupling to diverse MS platforms (i.e., triple quadrupole, linear ion trap and time of flight). Furthermore, as a proof of concept, we evaluated CBS-MS as a tool for quantitation of fentanyl and four analogues on said instruments. Custom-made MS interfaces were made to accurately position the blade in front of the MS inlet. CBS devices, coated with hydrophilic-lipophilic balanced particles, were used for both the optimization of the CBS position and the quantitation of fentanyl and analogues in urine and plasma samples on all instruments. The SCIEX triple quadrupole instrument was the most sensitive to the position of the blade due to the presence of a curtain gas flowing laminarly out of the MS inlet. After optimization, the analytical capabilities of CBS on each instrument were assessed and the results obtained on both SCIEX and Waters platforms matched the performance obtained using a more advanced instrument by ThermoFisher Scientific. Furthermore, excellent figures of merit were attained for the quantitation of fentanyl and analogues on both triple quadrupole and linear ion trap platforms. We demonstrated that optimization of MS parameters on different instrument vendors and front ends, such as the position of the CBS tip regarding the MS inlet, is vital to exploit the full quantitative potential of this technology. Application of the technology to screen and quantify fentanyl and analogues showed great potential when considering its coupling with portable mass spectrometers for therapeutic drug monitoring and point-of-care applications.

Commissioning of the St. Benedict RF carpet

The Superallowed Transition BEta NEutrino Decay Ion Coincidence Trap (St. Benedict) aims to measure the beta-neutrino angular correlation parameter for superallowed mixed beta decay transitions between mirror nuclei in order to conduct precision tests of the Standard Model. St. Benedict will include a gas catcher, a differentially pumped extraction system, a radio-frequency quadrupole (RFQ) cooler and buncher, and a Paul trap to utilize radioactive ion beams produced at the Nuclear Science Laboratory of the University of Notre Dame. The two-part differentially pumped extraction system contains a RF carpet at a helium gas pressure of around 3 mbar, and a radio-frequency quadrupole (RFQ) ion guide at a pressure of around 2×10−3 mbar. Transport efficiency of potassium ions in the first part of the extraction system using the RF carpet in the presence of gas flow was determined to be near 100% in the 0.75 to 5 mbar pressure range using the ion surfing transport method.

Nano- and microparticle Nonlinear Damping Identification in quadrupole trap

We propose a Nonlinear Damping Identification method for charged nano- and microparticles in a linear quadrupole Paul trap under nonlinear damping forces. We analytically and numerically evaluate conditions for the formation of plane limit cycle trajectories, i.e. “extended orbits” in spherical particle approximation. We introduce numerical metrics for such orbits and define a functional relation between the metrics and physical parameters of a trapped particle: size, mass, and charge. The method proposed allows non-destructive, simultaneous and separate determination of the trapped particle parameters in a wide range of sizes.