Ion Trap Mass Spectrometer Research Articles

Toward XUV frequency comb spectroscopy of the 1 S–2 S transition in hbox {He}^+

The energy levels of hydrogen-like atoms and ions are accurately described by bound-state quantum electrodynamics (QED). hbox {He}^{+} ions have a doubly charged nucleus, which enhances the higher-order QED contributions and makes them interesting for precise tests of QED. Systematic effects that currently dominate the uncertainty in hydrogen spectroscopy, such as the second-order Doppler shift and time-of-flight broadening, are largely suppressed by performing spectroscopy on trapped and cooled hbox {He}^{+} ions. Measuring a transition in hbox {He}^{+} will extend the test of QED beyond the long-studied hydrogen. In this article, we describe our progress toward precision spectroscopy of the 1 S–2 S two-photon transition in hbox {He}^{+}. The transition can be excited by radiation at a wavelength of 60.8 nm generated by a high-power infrared frequency comb using high-order harmonic generation (HHG). The hbox {He}^{+} ions are trapped in a Paul trap and sympathetically cooled with laser-cooled hbox {Be}^{+} ions. Our recently developed signal detection scheme based on secular-scan spectrometry is capable of detecting hbox {He}^{+} excitation with single-event sensitivity.Graphic abstract

Content determination of ten flavonoids and alkaloids in Gleditsiae Sinensis Fructus, Gleditsiae Fructus Abnormalis, and Gleditsiae Spina

To study the quality control of three traditional Chinese medicines derived from Gleditsia sinensis [Gleditsiae Sinensis Fructus(GSF), Gleditsiae Fructus Abnormalis(GFA), and Gleditsiae Spina(GS)], this paper established a multiple reaction monitoring(MRM) approach based on ultra-high performance liquid chromatography-triple quadrupole-linear ion-trap mass spectrometry(UHPLC-Q-Trap-MS). Using an ACQUITY UPLC BEH C_(18) column(2.1 mm × 100 mm, 1.7 μm), gradient elution was performed at 40 ℃ with water containing 0.1% formic acid-acetonitrile as the mobile phase running at 0.3 mL·min~(-1), and the separation and content determination of ten chemical constituents(e.g., saikachinoside A, locustoside A, orientin, taxifolin, vitexin, isoquercitrin, luteolin, quercitrin, quercetin, and apigenin) in GSF, GFA, and GS were enabled within 31 min. The established method could quickly and efficiently determine the content of ten chemical constituents in GSF, GFA, and GS. All constituents showed good linearity(r>0.995), and the average recovery rate was 94.09%-110.9%. The results showed that, the content of two alkaloids in GSF(2.03-834.75 μg·g~(-1)) was higher than that in GFA(0.03-10.41 μg·g~(-1)) and GS(0.04-13.66 μg·g~(-1)), while the content of eight flavonoids in GS(0.54-2.38 mg·g~(-1)) was higher than that in GSF(0.08-0.29 mg·g~(-1)) and GFA(0.15-0.32 mg·g~(-1)). These results provide references for the quality control of G. sinensis-derived TCMs.

Determination of the B8 neutrino energy spectrum using trapped ions

The ${\ensuremath{\beta}}^{+}$ decay of $^{8}\mathrm{B}$ provides the dominant source of solar neutrinos above 2 MeV. Consequently, experiments that detect neutrinos from the sun require an accurate determination of the $^{8}\mathrm{B}$ neutrino energy spectrum. In this work, the $\ensuremath{\beta}$-decay Paul trap surrounded by double-sided silicon strip detectors was utilized to precisely measure the decay products of trapped $^{8}\mathrm{B}$ ions. The results were used to determine the $^{8}\mathrm{Be}$ final-state distribution and to reconstruct the neutrino energy spectrum. This measurement using trapped ions is the first of its kind and puts the neutrino energy spectrum on much firmer footing by discriminating between recently reported values for the maximum of the final-state distribution.

Observation of Slow Eigen-Zundel Interconversion in H+(H2O)6 Clusters upon Isomer-Selective Vibrational Excitation and Buffer Gas Cooling in a Cryogenic Ion Trap.

The formation of isomers when trapping floppy cluster ions in a temperature-controlled ion trap is a generally observed phenomenon. This involves collisional quenching of the ions initially formed at high temperature by buffer gas cooling until their internal energies fall below the barriers in the potential energy surface that separate them. Here we explore the kinetics at play in the case of the two isomers adopted by the H+(H2O)6 cluster ion that differ in the proton accommodation motif. One of these is most like the Eigen cation with a tricoordinated hydronium motif (denoted E), and the other is most like the Zundel ion with the proton equally shared between two water molecules (denoted Z). After initial cooling to about 20 K in the radiofrequency (Paul) trap, the relative populations of these two spectroscopically distinct isomers are abruptly changed through isomer-selective photoexcitation of bands in the OH stretching region with a pulsed (∼6 ns) infrared laser while the ions are in the trap. We then monitor the relaxation of the vibrationally excited clusters and reformation of the two cold isomers by recording infrared photodissociation spectra with a second IR laser as a function of delay time from the initial excitation. The latter spectra are obtained after ejecting the trapped ions into a time-of-flight photofragmentation mass spectrometer, thus enabling long (∼0.1 s) delay times. Excitation of the Z isomer is observed to display long-lived vibrationally excited states that are collisionally cooled on a ms time scale, some of which quench into the E isomer. These excited E species then display spontaneous interconversion to the Z form on a ∼10 ms time scale. These qualitative observations set the stage for a series of experimental measurements that can provide quantitative benchmarks for theoretical simulations of cluster dynamics and the potential energy surfaces that underlie them.

Ultra-low current electrospray ionization of chloroform solution for the analysis of perfluorinated sulfonic acids.

Femtoamp and picoamp electrospray ionization (ESI) characteristics of a nonpolar solvent were explored. The direct ESI mass spectrometry analysis of chloroform extract solution enabled rapid analysis of perfluorinated sulfonic acid analytes in drinking water. Neat chloroform solvent and extracts were directly used in a typical wire-in ESI setup using micrometer emitter tips. Ionization currents were measured with femtoamp sensitivity while ramping the spray voltage from 0 to -5000 V. Methanol was used as a comparison to illustrate thecharacteristics of electrospraying chloroform. The effects of spray voltage and inlet temperature were studied. A liquid-liquid extraction workflow was developed to analyze perfluorooctanoate sulfonate (PFOS) in drinking water using an ion-trap mass spectrometer. The ionization onset of chloroform solution was 41 ± 17 fA at 300 V. The ionization current gradually increased with voltage while remaining below 100 pA when using voltages up to -5000 V. The ion signal of PFOS was significantly enhanced to improve the limit of detection (LoD) to 25 ppt in chloroform. Coupled with a liquid-liquid extraction workflow, LoD of 0.38-5.1ppt and a quantitation range of 5-400 ppt were achieved for perfluorinated sulfonic compounds in 1-ml water samples. Femtoamp and picoamp modes expand the solvent compatibility range of ESI and can enable quantitative analysis in parts per trillion (ppt) concentrations.

Effects of micromotion on the squeezing and on the dynamical behaviour of ion in a Paul trap

Effects of micromotion on the squeezing and on the dynamical behaviour of ion in a Paul trap

Evaluating the accuracy of absorbing aerosol optical properties measured using single particle cavity ring-down spectroscopy

Single particle cavity ring-down spectroscopy (CRDS) allows direct and continuous measurements of the extinction cross-sections for levitated micron-scale aerosol particles of constant or evolving composition. Our recent interests have concerned single particle CRDS measurements for light-absorbing particles. These measurements are made on single, spherical particles evaporating over the radius range 1500–700 nm that are levitated within a 405-nm cavity ring-down spectrometer using a linear electrodynamic quadrupole trap. Here, we quantify the accuracy and precision of our cavity ring-down time measurements and the consequences of particle motion within our electrodynamic trap. Next, we estimate the uncertainty in our particle size retrievals from angularly resolved elastic light scattering measurements for particles with a range of absorption strengths. Finally, we assess the accuracy of complex refractive index values retrieved from simultaneous ring-down time and particle size measurements. The assessments account for the impacts of shot and detector noise in the measured ring-down times, the driven particle motion within the electrodynamic trap, and particle absorption strength (for imaginary refractive indices in the range ∼0.0–0.1). The real and imaginary refractive indices are retrieved to an accuracy better than 0.005 and 0.002, respectively, for almost all absorption strengths studied, and for particles of constant or evolving composition. Although particles confined in our electrodynamic quadrupole trap undergo considerable levels of driven motion (with oscillation amplitudes of several tens of micrometers), the contribution of this motion to uncertainty in retrieved refractive indices is negligible compared to contributions from particle sizing errors.

3D sympathetic cooling and detection of levitated nanoparticles

Cooling the center-of-mass motion of levitated nanoparticles provides a route to quantum experiments at mesoscopic scales. Here we demonstrate three-dimensional sympathetic cooling and detection of the center-of-mass motion of a levitated silica nanoparticle. The nanoparticle is electrostatically coupled to a feedback-cooled particle while both particles are trapped in the same Paul trap. We identify two regimes, based on the strength of the cooling: in the first regime, the sympathetically cooled particle thermalizes with the directly cooled one, while in the second regime, the sympathetically cooled particle reaches a minimum temperature. This result provides a route to efficiently cool and detect particles that cannot be illuminated with strong laser light, such as absorptive particles, and paves the way for controlling the motion of arrays of several trapped nanoparticles.

Examining Interactions of Uranyl(VI) Ions with Amino Acids in the Gas Phase

Gas-phase experiments, using electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT/MS), were conducted to probe basic interactions of the uranyl(VI) ion, UO22+, with selected natural amino acids, namely, L-cysteine (Cys), L-histidine (His), and L-aspartic acid (Asp), which strongly bind to metal ions. The simplest amino acid, glycine (Gly), was also studied for comparison. Cys, His, and Asp have additional potentially coordinating groups beyond the amino and carboxylic acid functional groups, specifically thiol in Cys, imidazole in His, and a second carboxylate in Asp. Gas-phase experiments comprised collision-induced dissociation (CID) of uranyl–amino acid complexes and competitive CID to assess the relative binding strength of different amino acids in the same uranyl complex. Reactivity of selected uranyl–amino acid complexes with water provided further insights into relative stabilities. In positive ion mode, CID and ensuing reactions with water suggested that uranyl–neutral AA binding strength decreased in the order His > Asp > Cys > Gly, which is similar to amino acid proton affinities. In negative ion mode, CID revealed a decreasing dissociation tendency in the order Gly >> His ≈ Cys > Asp, presumably reflecting a reverse enhanced binding to uranyl of the doubly deprotonated amino acids formed in CID.

Comparison of APCI orbitrap MS and GCxGC/EI TOF MS for the hydrocarbon analysis of heavy base oils

The performance of positive-ion mode atmospheric pressure chemical ionization linear quadrupole ion trap orbitrap mass spectrometry (APCI LQIT Orbitrap MS) has been compared to that of two-dimensional gas chromatography coupled with positive-ion mode electron ionization time-of-flight mass spectrometry (GCxGC/EI TOF MS) for the analysis of group III heavy base oils. Upon APCI, all compounds were predominantly ionized via protonation. However, protonated alkanes are not stable and predominantly generated [M−H]+ ions via elimination of a hydrogen molecule from the protonated molecule. The high-resolution APCI mass spectra provided elemental composition information for the compounds while low-resolution APCI mass spectra were used for semiquantitative evaluation of the relative amounts of the compounds. Ions corresponding to compounds in seven hydrocarbon classes, i.e., (1) linear and branched alkanes, (2) monocycloalkanes, (3) dicycloalkanes, (4) tricycloalkanes and alkylbenzenes, (5) tetracycloalkanes, (6) pentacycloalkanes, and (7) hexacycloalkanes were identified. On the other hand, the GCxGC/EI TOF MS method enabled the chromatographic separation of most analytes. The measured EI mass spectra were used for the identification of the compounds while the GC peak areas were used for semiquantitative evaluation. The detected compounds were classified into three different hydrocarbon classes, (1) linear and branched alkanes, (2) cycloalkanes, and (3) aromatic hydrocarbons. The (+)APCI LQIT Orbitrap MS method was found to be faster and to provide more information for the larger compounds in the samples. For example, polycycloalkanes were only detected by using (+)APCI MS. However, no aromatic compounds were detected. Data processing was more straightforward than when using the GCxGC/EI TOF MS method. However, the latter method provided more accurate results for aromatic hydrocarbons and small alkanes as the analysis of small alkanes by using (+)APCI MS is limited due to the fact that [M−H]+ ions of small alkanes overlap with alkane fragment ions. Both light and heavy aliphatic and aromatic hydrocarbons were detected by using the GCxGC/EI TOF MS method but not polycycloalkanes. Therefore, these two methods complement each other, and each has different strengths and weaknesses.

Transient fluorescence with a single trapped ion

In this paper, we present a method to measure transient fluorescent dynamics with single trapped ions in a Paul trap. We use 40Ca+ ions that exhibit a Λ-type three-level system and measure the characteristic optical pumping times between the ground S1/2 and the meta-stable D3/2 levels. We prepare one of these states and then pump it to the opposite via the excited P1/2 state. By measuring the scattered photons of the ion, we retrieve transient curves of the atomic fluorescence. These curves provide fundamental information about the atomic system, such as branching fractions and excited-state lifetimes, as well as experimental parameters like the efficiency of the detection system and the saturation parameter of one of the transitions. Finally, we study the time-dependent fluorescence as a function of optical power and detuning of the lasers and find a very good agreement with simulating the dynamics via a three-level open quantum system through a set of optical Bloch equations. Being able to record time-dependent fluorescence is of particular interest as it contains information about the temperature, cooling, and heating dynamics of the ion.

Rapid screening of high-priority N-nitrosamines in pharmaceutical, forensic, and environmental samples with paper spray ionization and filter cone spray ionization-mass spectrometry.

The burgeoning concern of N-nitrosamine (NAM) contamination found in various pharmaceutical compositions has increased the demand for rapid and reliable screening methods to better assess the breadth of the problem. These carcinogenic compounds are also found in food, water, and soil, and they have been used in poison-related homicides. A combination of complementary, ambient ionization methods, paper spray ionization (PSI) and filter cone spray ionization (FCSI)-mass spectrometry (MS), was characterized towards trace-level residue screening of select NAMs (e.g., N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosodibutylamine) directly from complex and problematic matrices of interest, including prescription and over-the-counter tablets, drinking water, soil, and consumable goods. Spectral data for analyte confirmation and detection limit studies were collected using a Thermo LCQ Fleet ion trap mass spectrometer. PSI-MS and FCSI-MS readily produced mass spectral data marked by their simplicity (e.g., predominantly protonated molecular ions observed) and congruence with traditional electrospray ionization mass spectra in under 2min. per sample. Both methods proved robust to the complex matrices tested, yielding ion signatures for target NAMs, as well as active pharmaceutical ingredients for analyzed tablets, flavorants inherent to food products, etc. Low part-per-million detection limits were observed but were shown dependent on sample composition. PSI-MS and FCSI-MS were successful in detecting trace-level NAMS in complex liquid- and solid-phase matrices with little to no prior preparation. This work suggests that these methodologies can provide a means for assessing problematic pharmaceutical adulterants/degradants for expedited quality control, as well as enhancing environmental stewardship efforts and forensic investigations.

Identification of circular RNAs of Cannabis sativa L. potentially involved in the biosynthesis of cannabinoids.

We identified circRNAs in the Cannabis sativa L. genome and examined their association with 28 cannabinoids in three tissues of C. sativa. Nine circRNAs are potentially involved in the biosynthesis of six cannabinoids. Cannabis sativa L. has been widely used in the production of medicine, textiles, and food for over 2500years. The main bioactive compounds in C. sativa are cannabinoids, which have multiple important pharmacological actions. Circular RNAs (circRNAs) play essential roles in growth and development, stress resistance, and the biosynthesis of secondary metabolites. However, the circRNAs in C. sativa remain unknown. In this study, to explore the role of circRNAs in cannabinoid biosynthesis, we performed RNA-Seq and metabolomics analysis on the leaves, roots, and stems of C. sativa. We identified 741 overlapping circRNAs by three tools, of which 717, 16, and 8 circRNAs were derived from exonic, intronic, and intergenic, respectively. Functional enrichment analysis indicated that the parental genes (PGs) of circRNAs were enriched in many processes related to biological stress responses. We found that most of the circRNAs showed tissue-specific expression and 65 circRNAs were significantly correlated with their PGs (P < 0.05, |r|≥ 0.5). We also determined 28 cannabinoids by High-performance liquid chromatography-ESI-triple quadrupole-linear ion trap mass spectrometry. Ten circRNAs, including ciR0159, ciR0212, ciR0153, ciR0149, ciR0016, ciR0044, ciR0022, ciR0381, ciR0006, and ciR0025 were found to be associated with six cannabinoids by weighted gene co-expression network analysis. Twenty-nine of 53 candidate circRNAs, including 9 cannabinoids related were validated successfully using PCR amplification and Sanger sequencing. Taken together, all these results would help to enhance our acknowledge of the regulation of circRNAs, and lay the foundation for breeding new C. sativa cultivars with high cannabinoids through manipulating circRNAs.

Rydberg ions in coherent motional states: a new method for determining the polarizability of Rydberg ions

We present a method for measuring the polarizability of Rydberg ions confined in the harmonic potential of a Paul trap. For a highly excited electronic state, the coupling between the electronic wave function and the trapping field modifies the excitation spectra depending on the motional state of the ion. This interaction strongly depends on the polarizability of the excited state and manifests itself in the state-dependent secular frequencies of the ion. We initialize a single trapped 40Ca+ ion from the motional ground state into coherent states with up to 12 using electric voltages on the trap segments. The internal state, firstly initialised in the long-lived 3D state, is excited to a Rydberg S-state via the 5P state in a two-photon process. We probe the depletion of the 3D state owing to the Rydberg excitation followed by a decay into the internal ground 4S state. By analysing the obtained spectra we extract the polarizability of Rydberg states which agree with numerical calculations. The method is applicable to different Rydberg states regardless of their principal or angular quantum numbers. An accurate value of the state polarizability is needed for quantum gate operations with Rydberg ion crystals.

Vibrationally- and rotationally-resolved photoelectron imaging of cryogenically-cooled SbO2 –

We report a temperature-controlled photoelectron imaging study of SbO2 –, produced from a laser vaporisation source and cooled in a cryogenic 3D Paul trap. Vibrationally resolved photoelectron spectra are obtained for the ground state detachment transition, yielding the bending frequencies for both SbO2 and SbO2 –. Franck-Condon simulations also allow the estimate of the vibrational temperature of the trapped SbO2 – anion. A near-threshold spectrum of SbO2 – at a photon energy of 3.4958 eV reveals partially resolved rotational structure for the 0–0 transition, which yields an accurate electron affinity of 3.4945 ± 0.0004 eV for SbO2. The rotational simulation also yields an estimated rotational temperature of the trapped ions.

Modification of a Quadrupole/Orbitrap/Linear Quadrupole Ion Trap Tribrid Mass Spectrometer for Diagnostic Gas-Phase Ion–Molecule Reactions

Tandem mass spectrometry based on diagnostic gas-phase ion-molecule reactions represents a robust method for functional group identification in unknown compounds. To date, most of these reactions have been studied using unit-resolution instruments, such as linear quadrupole ion traps and triple quadrupoles, which cannot be used to obtain elemental composition information for the species of interest. In this study, a high-resolution mass spectrometer, a quadrupole/orbitrap/linear quadrupole ion trap tribrid, was modified by installing a portable reagent inlet system to obtain high-resolution data for ion-molecule reactions. Examination of a previously published test system, the reaction between protonated 1,1'-sulfonyldiimizadole with 2-methoxypropene, demonstrated the ability to perform ion-molecule reactions on the modified tribrid mass spectrometer. High-resolution data were obtained for ion-molecule reactions of three isobaric ions (protonated glycylalanine, protonated glutamine, and protonated lysine) with diethylmethoxyborane. On the basis of these data, the isobaric ions can be differentiated based on both their measured accurate mass as well as the different product ions they generated upon the ion-molecule reactions. In a different experiment, analyte ions were subjected to collision-induced dissociation (CID), and the structures of the resulting fragment ions were examined via diagnostic ion-molecule reactions. This experiment allows for the functional group interrogation of fragment ions and can be used to improve the understanding of the structures of fragment ions generated in the gas phase.

Simultaneous determination of 10 first-generation histamine h1 receptor blockers in feeds by ultra-high-performance liquid chromatography triple quadrupole ion trap hybrid mass spectrometer.

A method for simultaneous determination of 10 first-generation histamine H1 receptor blockers in feeds by ultra-high-performance liquid chromatography triple quadrupole mass spectrometry combined with solid phase extraction. Instrument conditions, extraction solvents, and purification methods have been optimized. Under the optimum conditions, these analytes were separated effectively at 6min. These feeds have been extracted by acid acetonitrile and purified by mixed cation exchange solid-phase extraction. The performance of this method meets the requirements of veterinary residue detection in feeds in China. It is appropriate for the confirmatory monitoring and quantitative analysis of 105 feed samples, five kinds of histamine H1 receptor blockers have been detected in 10 samples.

Effect of protonation on the UV/VUV photostability of cyano-substituted anthracene and phenanthrene

Context. The vacuum ultraviolet (VUV) photoprocessing of polycyclic aromatic hydrocarbons (PAHs) has been established as a key piece of the puzzle to understand the life cycle of carbon-based molecules in space. The recent detection of cyano (CN) aromatic species, with unexpectedly high abundance, motivated the current study of investigating their interaction with UV/VUV radiation. Aims. The aims were to investigate the fate, after VUV photoexcitatation, of medium-size (three rings) CN-PAH radical cations and of their protonated analogs, and thus to assess the effect of protonation on the photostability of the CN-PAHs. Photoproducts (ionic fragments and dications) were mass-analyzed and measured as a function of photon energy. The results were also compared with those for the bare anthracene radical cation to assess the influence of the added CN group. Methods. The positively charged CN-PAHs were stored in a quadrupole ion trap prior to interrogation by UV/VUV radiation, with photon energies between 4.5 and 13.6 eV, delivered by the DESIRS beamline from the synchrotron SOLEIL. Results. The HCN/HNC loss channel is present for both radical cations and protonated species, but H2 loss is only apparent for the radical cations. Based on comparison with quantum chemical calculations, radiative and/or collisional processes should be relevant at energies lower than 8 eV, with a stronger propensity for radical cation than protonated CN-PAHs. The cata-condensed 9-CN-anthracene has a nearly two-fold larger photoionization yield at 13.6 eV than peri-condensed 9-CN-phenanthrene. Conclusions. The photoionization yield of singly and doubly ionized CN-PAHs is greater for radical cations than for protonated analogs. The photoionization yields of CN-PAHs is diminished by protonation and, in the future, similar investigations should target larger protonated CN-PAHs to support a general model for the photo-processing of these relevant molecular systems. Similar processes to those for the bare PAH radical cations may involve the radical cations of CN-PAHs, making their addition important in models that describe the photoelectric heating of interstellar gas.

Dynamics Inside a Dual-Frequency Paul Trap in the Presence of Excess Micromotion

Dynamics inside a dual-frequency Paul trap is theoretically analyzed in the presence of excess micromotion on account of stray electric field and the field due to a mismatch of potential at the electrodes. The fields contributing to the excess micromotion have a strong influence on the kinetic energy of a single-charged particle, however, their influence is not profound when the collective dynamics of many charged particles is considered inside the trap. The collective dynamics is encapsulated by a distribution function whose time average is double-humped with respect to the velocity. The spatial variation of energyis asymmetrical. The temporal fluctuations of the energy are periodic with a period of variation depending upon the ratio of the two applied RF frequencies.

Sympathetic cooling and squeezing of two colevitated nanoparticles

Levitated particles are an ideal tool for measuring weak forces and investigating quantum mechanics in macroscopic objects. Arrays of two or more of these particles have been suggested for improving force sensitivity and entangling macroscopic objects. In this article, two charged, silica nanoparticles, that are coupled through their mutual Coulomb repulsion, are trapped in a Paul trap, and the individual masses and charges of both particles are characterized. We demonstrate sympathetic cooling of one nanoparticle coupled via the Coulomb interaction to the second nanoparticle to which feedback cooling is directly applied. We also implement sympathetic squeezing through a similar process showing nonthermal motional states can be transferred by the Coulomb interaction. This work establishes protocols to cool and manipulate arrays of nanoparticles for sensing and minimizing the effect of optical heating in future experiments.