Quadrupole Trap Research Articles

Systematic Mapping of Posttranslational Modifications in Human Estrogen Receptor-α with Emphasis on Novel Phosphorylation Sites

A systematic study of posttranslational modifications of the estrogen receptor isolated from the MCF-7 human breast cancer cell line is reported. Proteolysis with multiple enzymes, mass spectrometry, and tandem mass spectrometry achieved very high sequence coverage for the full-length 66-kDa endogenous protein from estradiol-treated cell cultures. Nine phosphorylated serine residues were identified, three of which were previously unreported and none of which were previously observed by mass spectrometry by any other laboratory. Two additional modified serine residues were identified in recombinant protein, one previously reported but not observed here in endogenous protein and the other previously unknown. Although major emphasis was placed on identifying new phosphorylation sites, N-terminal loss of methionine accompanied by amino acetylation and a lysine side chain acetylation (or possibly trimethylation) were also detected. The use of both HPLC-ESI and MALDI interfaced to different mass analyzers gave higher sequence coverage and identified more sites than could be achieved by either method alone. The estrogen receptor is critical in the development and progression of breast cancer. One previously unreported phosphorylation site identified here was shown to be strongly dependent on estradiol, confirming its potential significance to breast cancer. Greater knowledge of this array of posttranslational modifications of estrogen receptor, particularly phosphorylation, will increase our understanding of the processes that lead to estradiol-induced activation of this protein and may aid the development of therapeutic strategies for management of hormone-dependent breast cancer.

Magnetic Trapping of Hydrogen after Multistage Zeeman Deceleration

We report the first experimental realization of magnetic trapping of a sample of cold radicals following multistage Zeeman deceleration of a pulsed supersonic beam. H atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 520 m/s to 100 m/s in a 12-stage Zeeman decelerator and loaded into a magnetic quadrupole trap by rapidly switching the fields of the trap solenoids.

Cryogenic buffer-gas loading and magnetic trapping of CrH and MnH molecules

We report on the buffer-gas cooling and trapping of CrH and MnH molecules in a magnetic quadrupole trap with densities on the order of ${10}^{6}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ at a temperature of $650\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. Storage times of up to $180\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ have been observed, corresponding to a 20-fold lifetime enhancement with respect to the field-free diffusion through the $^{3}\mathrm{He}$ buffer-gas. Using Monte Carlo trajectory simulations, inelastic molecule-$^{3}\mathrm{He}$ collision cross sections of $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}$ and $3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ are extracted for CrH and MnH, respectively. Furthermore, elastic molecule-$^{3}\mathrm{He}$ collision cross sections of $1.4(\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ are determined for both species. We conclude that the confinement time of these molecules in a magnetic trapping field is limited by inelastic collisions with the helium atoms leading to Zeeman relaxation.

The Haemophilus influenzae HMW1 Adhesin Is a Glycoprotein with an Unusual N-Linked Carbohydrate Modification

The Haemophilus influenzae HMW1 adhesin mediates adherence to respiratory epithelial cells, a critical early step in the pathogenesis of H. influenzae disease. In recent work, we demonstrated that HMW1 undergoes glycosylation. In addition, we observed that glycosylation of HMW1 is essential for HMW1 tethering to the bacterial surface, a prerequisite for HMW1-mediated adherence to host epithelium. In this study, we examined HMW1 proteolytic fragments by mass spectrometry, achieved 89% amino acid sequence coverage, and identified 31 novel modification sites. All of the modified sites were asparagine residues, in all but one case in the conventional consensus sequence of N-linked glycans, viz. NX(S/T). Liquid chromatography-tandem mass spectrometry analysis using a hybrid linear quadrupole ion trap Fourier transform ion cyclotron mass spectrometer, accurate mass measurements, and deuterium exchange studies established that the modifying glycan structures were mono- or dihexoses rather than the N-acetylated chitobiosyl core that is characteristic of N-glycosylation. This unusual carbohydrate modification suggests that HMW1 glycosylation requires a glycosyltransferase with a novel activity.

Trapping of Intact, Singly-Charged, Bovine Serum Albumin Ions Injected from the Atmosphere with a 10-cm Diameter, Frequency-Adjusted Linear Quadrupole Ion Trap

High-resolution real-time particle mass measurements have not been achievable because the enormous amount of kinetic energy imparted to the particles upon expansion into vacuum competes with and overwhelms the forces applied to the charged particles within the mass spectrometer. It is possible to reduce the kinetic energy of a collimated particulate ion beam through collisions with a buffer gas while radially constraining their motion using a quadrupole guide or trap over a limited mass range. Controlling the pressure drop of the final expansion into a quadrupole trap permits a much broader mass range at the cost of sacrificing collimation. To achieve high-resolution mass analysis of massive particulate ions, an efficient trap with a large tolerance for radial divergence of the injected ions was developed that permits trapping a large range of ions for on-demand injection into an awaiting mass analyzer. The design specifications required that frequency of the trapping potential be adjustable to cover a large mass range and the trap radius be increased to increase the tolerance to divergent ion injection. The large-radius linear quadrupole ion trap was demonstrated by trapping singly-charged bovine serum albumin ions for on-demand injection into a mass analyzer. Additionally, this work demonstrates the ability to measure an electrophoretic mobility cross section (or ion mobility) of singly-charged intact proteins in the low-pressure regime. This work represents a large step toward the goal of high-resolution analysis of intact proteins, RNA, DNA, and viruses.

Advanced mass spectrometry techniques for identification, characterisation and structural elucidation of natural products

Mass-based structural identification of natural products frequently employs combinations of different mass spectrometers, including triple quadrupole and ion trap instruments. These methods often provide adequate information for tentatively identifying structures of analogues of previously characterized compounds. For completely unknown compound, tentatively identified structures are often further examined by high-resolution MS, from which elemental compositions can be obtained. Here it is required to measure the mass-to-charge ratios with the smallest mass uncertainties possible. Ideally, routines with sufficient resolution and mass accuracy yield single empirical formulae for every compound analysed. In the absence of a unique empirical formula, analysis can be highly ambiguous. In most studies, quadrupole TOF and Fourier-transform MS (orbitrap, ICR) instruments are used. This presentation illustrates state-of-the-art techniques for screening and identifying natural products. (1) Characterization of hyperforin in extracts of St. John's wort (Hypericum perforatum) is illustrated. The strategy used was a combination of MS2 and MS3 experiments, performed on QqLIT and high-resolution FTICR instruments. This combination allowed fragmentation schemes and chemical structures to be proposed. (2) Analysis of Boswellia from the Boswellia serrata tree is demonstrated. Specific active anti-inflammatory ingredients in this herb have been identified, boswellic acids. In animal studies, these acids have been shown to significantly reduce inflammation. We are interested in the metabolism, as the clinical efficiency appears high despite the low observed plasma levels, possibly involving unknown metabolites. (3) Characterization of active species in marine toxin extracts is shown. Analysis of phytoplankton allowed for detection of several previously characterized toxins as well as new unexpected compounds. Purification of crude extracts into several fractions using mass-triggered preparative chromatography permitted enrichment of different species, resulting in high quality mass spectra for all known and unknown species

Numerical calculations of potential distribution in non-ideal quadrupole trap and simulations of anharmonic oscillations

A quadrupole ion trap consisting of electrode structures symmetric about z-axis is an important tool for conducting several precision experiments. In practice the field inside the trap does not remain purely quadrupolar, and can be calculated using numerical methods. We have used boundary element method to calculate the potential inside the truncated as well as symmetrically misaligned quadrupolar ion trap. The calculated potential values are fitted to multipole expansion and the weights of multipole moments have been evaluated by minimizing the least square deviation. The higher-order multipole contribution in the fabricated hyperbolic electrodes due to truncation and machining imperfections is discussed. Non-linear effects arising due to the superposition of octupole moment manifest as anharmonic oscillations of trapped ions in the non-ideal Paul trap. Theoretical simulations of non-linear effects have been carried out.

Monte Carlo Simulation of Cooling Induced by Parametric Resonance

We demonstrate that the parametric resonance in a magnetic quadrupole trap can be exploited to cool atoms by using Bird's method. In our programme the parametric resonance was realized by anisotropically modulating the trap potential. The modulation frequency dependences of temperature and fraction of the trapped atoms are explored. Furthermore, the temperature after the modulation as functions of the modulation amplitude and the mean elastic collision time are also studied. These results are valuable for the experiment of parametric resonance in a quadrupole trap.

磁四极阱中参量共振诱导的原子冷却

It is demonstrated experimentally that the anharmonic property of the quadrupole trap can be exploited to cool trapped atoms by modulating the trap potential anisotropically. This cooling effect arises from the energy-selective removal of the most energetic trapped atoms and the thermal equilibrium of the remaining atoms. The frequency dependences of the temperature and the fraction of the atoms left in the trap after the modulation are explored. It is also demonstrated that the cooling induced by parametric resonance can also increase the phase space density of the trapped atoms.

Achievement of Energy Focus for Distance-of-Flight Mass Spectrometry with Constant Momentum Acceleration and an Ion Mirror

Distance-of-flight mass spectrometry (DOF-MS) has not yet been implemented, though it has many potential advantages in a variety of applications. Impeding the implementation of DOF-MS is the development of the required array detectors and working out the equivalents to the focusing methods now used in time-of-flight (TOF) mass analyzers. Ideally, a batch of ions composed of a variety of m/z values, despite initial distributions of space and energy, would be spatially focused at their respective flight distances at the same time. First-order energy focusing, including ion turnaround, is shown to be accomplished by the use of an ion mirror in conjunction with constant momentum acceleration of the initial ion packet. The initial spatial dispersion is maintained throughout the flight path. With zero initial spatial ion spread, energy focusing to achieve resolutions in the tens of thousands is shown to be feasible with ions from the elemental and isotope ratio mass regions through the extremely high m/z range. With moderate spatial spread taken into account, the DOF-MS approach is shown to achieve resolutions competitive with quadrupole and ion trap mass analyzers. Advantages of DOF-MS include all the advantages of TOF-MS plus simpler detector electronics and the improved signal-to-noise ratio and dynamic range afforded by array detection.

The use of a quadrupole electrostatic trap to transfer the dimensions of the volt in the 10 V–10 kV range

The problems involved in using a quadrupole trap for charged particles in order to increase the accuracy of the measurement of dc voltage in the 10 V–10 kV range are considered.

Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

We study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (rf) field. Chromium atoms $(^{52}\mathrm{Cr})$ in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In the presence of a rf field, the temperature of the metastable atoms that remain magnetically trapped can be as low as $25\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{K}$, with a density of ${10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$, resulting in an increase of the phase-space density, still limited to $7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the rf-truncated magnetic trap, and deduce the average elastic cross section for atoms in the $^{5}D_{4}$ metastable states, ${\ensuremath{\sigma}}_{el}=7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$.

Considerations on MS/MS Detection of Bromazepam after Liquid Chromatographic Separation from Plasma Samples: Application to a Bioequivalence Study

Bromazepam was isolated from plasma samples by simple protein precipitation with acetonitrile. A high throughput isocratic reversed phase separation between bromazepam and nitrazepam (IS) was achieved within 2 minutes on a rapid resolution cartridge column Zorbax SB‐C18, using methanol/aqueous 0.1% formic acid 40/60 (v/v) as mobile phase. Detection was made by tandem mass spectrometry, using the multiple reaction monitoring mode (MRM). Both electrospray (ESI) and atmospheric pressure chemical (API) ionizations modes were considered, together with triple quadrupole (TQ) and ion trap (IT) mass analyzers. Ionization patterns are discussed; no major differences being observed between ESI and API. Higher sensitivity was obtained when using the TQ mass analyzer. Comparison between different ionization modes/mass analyzers types is made, based on bromazepam concentration/time profiles in real plasma samples. The best results were obtained in ESI/TQ conditions. Consequently, the method was fully validated, and then applied to a single dose (6 mg) open label, randomized, two period, two sequence, and crossover bioequivalence study of bromazepam in two commercially available tablet formulations. A low limit of quantification (LOQ) at 2.5 ng/mL level was obtained. Precision below 3% (expressed as relative standard deviation) and accuracy (expressed as % bias) within −7 and +11% were achieved. Pharmacokinetic parameters are presented, being in good accordance with literature data.

An experiment on the Rayleigh instability of charged liquid drops

We describe a simple experiment to observe the fission of an electrically charged liquid droplet. Rayleigh charge instability occurs when the electrostatic repulsion of charges on the surface of a droplet overcomes the droplet surface tension and tears the droplet apart. The experiment requires a low-power laser, simple optics, a CCD camera, and a quadrupole trap, which can be constructed using widely available and relatively straightforward instructions. The experiment was performed primarily by undergraduates as part of their senior research projects and can be implemented readily in an advanced undergraduate physics laboratory course.

The Sputtering of Dust Grains: Aspects of Experimental Observations

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Dust grains are sputtered at every environment containing energetic ions (i.e., ions with energies of several kiloelectronvolts). In the laboratory, only the beam experiments would fulfill these conditions; however, in the space, ions of these energies can be found even in the solar wind. It was suggested that the sputtering is one of the most important destruction processes of micrometer-sized dust grains, and on the other hand, it would be a source of heavy species in the interplanetary medium. We simulate the space environment by trapping the dust grains in an electrodynamic quadrupole trap and by influencing them by the ion beam with a variable energy up to 5 keV. The grains are charged to high surface potentials, and thus, a strong electric field near the surface can affect the sputtering rate. The finite size and the small curvature radius of grains play an important role in the quantification of sputtering efficiency. We propose a simple sputtering model for spherical grains and compare its predictions with measurements. An interpretation of the preliminary results obtained on gold microspheres bombarded by argon ions indicates that not only the grain mass but also the grain shape is changing in the course of our experiment. We suggest that similar effects can occur in the space if the dust is exposed to collimated ion beams. </para>

Negative energy resonances of bosons in a magnetic quadrupole trap

We investigate resonances of spin 1 bosons in a three-dimensional magnetic quadrupole field. Complementary to the well-known positive energy resonances it is shown that there exist short-lived, i.e. broad, negative energy resonances. The latter are characterized by an atomic spin that is aligned antiparallel to the local magnetic field direction. In contrast to the positive energy resonances the lifetimes of the negative energy resonances decreases with increasing total magnetic quantum number. We derive a mapping of the two branches of the spectrum.

High Performance Liquid Chromatography/Atmospheric Pressure Ionization/Tandem Mass Spectrometry (HPLC/API/MS/MS) in Drug Metabolism and Toxicology

Studies of the metabolic fate of drugs and other xenobiotics in living systems may be divided into three broad areas: (1) elucidation of biotransformation pathways through identification of circulatory and excretory metabolites (qualitative studies); (2) determination of pharmacokinetics of the parent drug and/or its primary metabolites (quantitative studies); and (3) identification of chemically-reactive metabolites, which play a key role as mediators of drug-induced toxicities (mechanistic studies). Mass spectrometry has been regarded as one of the most important analytical tools in studies of drug metabolism, pharmacokinetics and biochemical toxicology. With the commercial introduction of new ionization methods such as those based on atmospheric pressure ionization (API) techniques and the combination of liquid chromatography-mass spectrometry (LC-MS), it has now become a truly indispensable technique in pharmaceutical research. Triple stage quadrupole and ion trap mass spectrometers are presently used for this purpose, because of their sensitivity and selectivity. API-TOF mass spectrometry has also been very attractive due to its enhanced full-scan sensitivity, scan speed, improved resolution and ability to measure the accurate masses for protonated molecules and fragment ions. This review aims to survey the utility of mass spectrometry in drug metabolism and toxicology and to highlight novel applications and future trends in this field.

Profiling of phenolic glycosidic conjugates in leaves of Arabidopsis thaliana using LC/MS

Profiling of plant secondary metabolites is still a very difficult task. Liquid chromatography (LC) or capillary electrophoresis hyphenated with different kinds of detectors are methods of choice for analysis of polar, thermo labile compounds with high molecular masses. We demonstrate the applicability of LC combined with UV diode array or/and mass spectrometric detectors for the unambiguous identification and quantification of flavonoid conjugates isolated from Arabidopsis thaliana leaves of different genotypes and grown in different environmental conditions. During LC/UV/MS/MS analyses we were able to identify tetra-, tri-, and di-glycosides of kaempferol, quercetin and isorhamnetin. Based on our results we can conclude that due to the co-elution of different chemical compounds in reversed phase HPLC systems the application of UV detectors does not allow to precisely profile all flavonoid conjugates existing in A. thaliana genotypes. Using MS detection it was possible to unambiguously recognize the glycosylation patterns of the aglycones. However, from the mass spectra we could not conclude neither the anomeric form of the C-1 carbon atoms of sugar moieties in glycosidic bonds between sugars or sugar and aglycone nor the position of the second carbon involved in disaccharides. The applicability of collision induced dissociation techniques (CID MS/MS) for structural analyses of the studied group of plant secondary metabolites with two types of analyzers (triple quadrupole or ion trap) was demonstrated.

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.

Mass spectral characterization of ergot alkaloids by electrospray ionization, hydrogen/deuterium exchange, and multiple stage mass spectrometry: usefulness of precursor ion scan experiments

Six ergot alkaloids belonging to the lysergic acid derivatives (ergonovine (EGN) and methysergide hydrogen maleinate (MHM)) and peptide-type derivatives (ergocristine (EGR), ergotamine (EGT), ergocornine (EGC) and alpha-ergokryptine (EGK)) were studied by positive electrospray tandem mass spectrometry. The fragmentation mechanisms of these compounds were studied by collision-induced dissociation (CID) using triple quadrupole and ion trap mass spectrometers, and the nature of the major product ions further confirmed by hydrogen/deuterium (H/D) exchange experiments. A common abundant product ion at m/z 223 was characteristic of the two classes of ergot alkaloids. Therefore, a precursor ion scan of m/z 223 that triggers information data acquisition (IDA) in combination with CID experiments was used to identify other potential ergot alkaloids. Using this approach, it was possible to confirm the presence of ergosine, another peptide-type ergot alkaloid, in a rye flour extract at trace levels.