•Simulations show classical chaotic behavior of ion motion in a toroidal ion trap.•Chaotic motion is caused by nonlinear higher-order terms in the electric field.•The chaotic motion may affect several aspects of trap performance.Although widely used in mass spectrometry, radiofrequency ion traps involve complex electric field shape and correspondingly complex ion motion. In addition, numerous variations of electrode geometry have been developed to address or benefit from different aspects of ion motion and the resulting effects on performance as a mass analyzer. We report on SIMION simulations that show classical chaotic behavior of ions in the toroidal ion trap. The chaotic motion is a result of the non-linear components of the electric fields as established by the trap electrodes, and not by Coulombic interaction from other ions. The chaotic behavior was observed specifically in the ejection direction of ions located in non-linear resonance bands within and adjacent to the region of stable trapping. The non-linear bands crossing through the stability regions correspond to hexapole resonance conditions, while the chaotic ejection observed at the boundary of the stable trapping region represents a “fuzzy” ejection boundary. Fractal-like patterns were obtained in a series of zoomed-in regions of the stability diagram.Download high-res image (113KB)Download full-size image

Herein we report an abnormal adsorption and desorption behavior where a stronger adsorption interaction between polystyrene particles and pharmaceutical drugs results in preferable desorption behavior. This behavior is contrary to the conventional view, in which a weaker adsorption interaction would lead to a more favorable desorption behavior of target molecules at solid surfaces. Different from other materials, numerous experimental results from a combination of mass spectrometry and infrared spectroscopy indicated quantitatively that the adsorption and desorption behavior of pharmaceutical drugs on polystyrene were independent of drug structure and solvent, while the intermolecular hydrogen bond interaction between polystyrene and the drug played a critical role in determining the adsorption and desorption behavior.

A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline.

We report a linear ion trap (LIT) in which the electric field is formed by fine wires held under tension and accurately positioned using holes drilled in two end plates made of plastic. The coordinates of the hole positions were optimized in simulation. The stability diagram and mass spectra using boundary ejection were compared between simulation and experiment and good agreement was found. The mass spectra from experiments show peak widths (fwhm) in units of mass-to-charge of around 0.38 Th using a scan rate of 3830 Th/s. The limits of detection are 137 ppbv and 401 ppbv for benzene and toluene, respectively. Different sizes of the wire ion trap can be easily fabricated by drilling holes in scaled positions. Other distinguishing features, such as high ion and photon transmission, low capacitance, high tolerance to mechanical and assembly error, and low weight, are discussed.

•Solutions of Laplace equation in toroidal coordinates allow analysis of toroidal ion traps.•Ion trapping and stability diagram in a quadrupole-like potential in toroidal space.•Comparison with conventional, Cartesian quadrupole devices.Although toroidal ion traps are being used more widely in miniaturized mass spectrometers, there is a lack of fundamental understanding of how the toroidal electric field affects ion motion, and therefore, the ion trap's performance as a mass analyzer. Toroidal harmonics, which represent solutions to the Laplace equation in a toroidal coordinate system, may be useful to understand these devices. This paper reports on SIMION simulations of ion trapping and ion motion in a time-varying electric potential representing the symmetric, second-order toroidal harmonic of the second kind—the solution most analogous to the conventional, Cartesian quadrupole. Simulations show that this potential, which we call the toroidal quadrupole, is similar to that of the Cartesian quadrupole in its ability to trap ions. The stability diagram for the toroidal quadrupole shares similarities with that of both the quadrupole ion trap (QIT) and the quadrupole mass filter (QMF), but has several minor differences including a series of chasms and a portion of the boundary that is diffuse.

•Potential mapping of the trapping region of toroidal ion trap designs.•Higher-order term calculations for fields of toroidal ion trap designs.•Ion simulation with and without ion–neutral collisions in toroidal ion trap designs.Potential mapping, field calculations, and simulations of ion motion were used to compare three types of toroidal ion traps: a symmetric and an asymmetric trap made using hyperbolic electrodes, and a simplified trap made using cylindrical electrodes. Higher-order components of the radial electric fields in the simplified design were similar to those of the axial field in the symmetric design, while the asymmetric design had minimal higher-order field contributions. Because of the toroidal geometry of the trapping region, an effect similar to centripetal force was observed in the motion of ions with a significant tangential component of velocity. The result of this effect is that the mean ion location is offset from the theoretical trapping center (the saddle point in the potential). A radial asymmetry in the micromotion was also observed. The average radial position, average kinetic energy, and average velocity were calculated for different trap conditions (temperature and pressure).

The survivability of Bacillus subtilis spores and vegetative Escherichia coli cells after electrospray from aqueous suspension was tested using mobility experiments at atmospheric pressure. E. coli did not survive electrospray charging and desolvation, but B. subtilis did. Experimental conditions ensured that any surviving bacteria were de-agglomerated, desolvated, and electrically charged. Based on mobility measurements, B. subtilis spores survived even with 2,000–20,000 positive charges. B. subtilis was also found to survive introduction into vacuum after either positive or negative electrospray. Attempts to measure the charge distribution of viable B. subtilis spores using electrostatic deflection in vacuum were inconclusive; however, viable spores with low charge states (less than 42 positive or less than 26 negative charges) were observed.

A radiofrequency toroidal ion trap mass analyzer comprised of four cylindrical electrodes is described. The ion trap consists of two RF electrodes and an AC electrode that surround a central electrode. Mass-analyzed ions are ejected through a slit in the central cylinder. A conversion dynode and electron multiplier are contained within the central cylinder for ion detection. The orientation of the RF and AC electrodes allows for inward-radial ejection of ions, removing the need for ion collection optics. Resolution of the toluene m/z 91 ion was determined for both a forward mass selective instability scan as well as for a reverse scan with resonant ejection. These experiments were performed in parallel with the stretching and compressing of the RF ring electrode spacing. Experimental resolution (Δm) values compare well with previous toroidal ion traps. The stability diagram for the toluene m/z 91 ion is also reported. The diagram possesses a slightly asymmetric profile due to asymmetry of the trapping dimensions as well as the curvature of the toroidal trapping region. Finally, the tandem (MS2) mass spectrum of iso-butylbenzene is reported.Graphical abstractHighlights► A toroidal ion trap mass analyzer utilizing cylindrical electrodes is presented. ► Resolution of toluene m/z 91 is evaluated for both scan direction and higher order multipole components. ► Optimal parameters yield resolution values superior to previously reported toroidal designs. ► The first stability diagram of an ion trap with a toroidal trapping geometry is presented and discussed. ► Tandem (MS2) mass spectrometry of iso-butylbenzene is demonstrated.

We present the design and results for a new radio-frequency ion trap mass analyzer, the coaxial ion trap, in which both toroidal and quadrupolar trapping regions are created simultaneously. The device is composed of two parallel ceramic plates, the facing surfaces of which are lithographically patterned with concentric metal rings and covered with a thin film of germanium. Experiments demonstrate that ions can be trapped in either region, transferred from the toroidal to the quadrupolar region, and mass-selectively ejected from the quadrupolar region to a detector. Ions trapped in the toroidal region can be transferred to the quadrupole region using an applied ac signal in the radial direction, although it appears that the mechanism of this transfer does not involve resonance with the ion secular frequency, and the process is not mass selective. Ions in the quadrupole trapping region are mass analyzed using dipole resonant ejection. Multiple transfer steps and mass analysis scans are possible on a single population of ions, as from a single ionization/trapping event. The device demonstrates better mass resolving power than the radially ejecting halo ion trap and better sensitivity than the planar quadrupole ion trap.

We report on the effects of varying higher-order multipole components on the performance of a novel radiofrequency quadrupole ion-trap mass analyzer, named the planar Paul trap. The device consists of two parallel ceramic plates, the opposing surfaces of which are lithographically imprinted with 24 concentric metal rings. Using this device, the magnitude and sign of different multipole components, including octopole and dodecapole, can be independently adjusted through altering the voltages applied to each ring. This study presents a systematic investigation of the effects of the octopole and dodecapole field components on the mass resolution and signal intensity of the planar Paul trap. Also, the effect of dipole amplitude and scan speed under both forward and reverse scan modes have been investigated for various combinations of octopole and dodecapole. A trapping field in which the magnitudes of the octopole and dodecapole are, respectively, set to 0% and +8% of the magnitude of the quadrupole yields the highest mass resolution under the conditions studied. A small threshold voltage for dipole resonance ejection is observed for positive octopole, and to a lesser extent for positive dodecapole, but not for negative poles. When both octopole and dodecapole are negative, a reverse scan produces higher resolution, but this effect is not observed when only one of the components is negative.Graphical abstractThis paper presents experimental data on the effect of multipole components on the performance of a two-plate quadrupole ion trap.Research highlights▶ Higher-order multipole components are varied individually in a novel quadrupole ion trap. ▶ Variations in octopole and dodecapole affect resolution, signal-to-noise, and dipole ejection. ▶ The results of forward vs. reverse scan are given for various combinations of higher-order fields.

The halo ion trap (IT) was modified to allow for axial ion ejection through slits machined in the ceramic electrode plates rather than ejecting ions radially to a center hole in the plates. This was done to preserve a more uniform electric field for ion analysis. An in-depth evaluation of the higher-order electric field components in the trap was also performed to improve resolution. The linear, cubic and quintic (5th order) electric field components for each electrode ring inside the IT were calculated using SIMION (SIMION version 8, Scientific Instrument Services, Ringoes, NJ, USA) simulations. The preferred electric fields with higher-order components were implemented experimentally by first calculating the potential on each electrode ring of the halo IT and then soldering appropriate capacitors between rings without changing the original trapping plate design. The performance of the halo IT was evaluated for 1% to 7% cubic electric field (A4/A2) component. A best resolution of 280 (m/Δm) for the 51-Da fragment ion of benzene was observed with 5% cubic electric field component. Confirming results were obtained using toluene, dichloromethane, and heptane as test analytes.

Ion trap mass analyzers made using arrays of independent electrodes allow unprecedented control and variability of electric field shapes. We present a method to select and implement specific values for higher-order multipoles, which are known to affect ion trapping and mass analysis in quadrupole ion traps. Electrode arrays are amenable to microfabrication techniques, hence this method can be used to improve performance in miniaturized ion trap mass spectrometers. With ion traps made using two opposing electrode array plates, both even- and odd-order multipoles can be independently adjusted.A method is presented to independently select and optimize higher-order multipoles in quadrupole ion traps made using two plates with lithographically-patterned electrode arrays.

We report the design and performance of a novel radio-frequency (RF) ion-trap mass analyzer, the planar Paul trap, in which a quadrupolar potential distribution is made between two electrode plates. Each plate consists of a series of concentric, lithographically deposited 100-μm-wide metal rings, overlaid with a thin resistive layer. A different RF amplitude is applied to each ring, such that the trapping field produced is similar to that of the conventional Paul trap. The accuracy and shape of the electric fields in this trap are not limited by electrode geometry nor machining precision, as is the case in traps made with metal electrodes. The use of two microfabricated plates for ion trap construction presents a lower-cost alternative to conventional ion traps, with additional advantages in electrode alignment, electric field optimization, and ion-trap miniaturization. Experiments demonstrate the effects of ion ejection mode and scan rate on mass resolution for several small organic compounds. The current instrument has a mass range up to ∼180 Thomsons (Th), with better than unit mass resolution over the entire range.

In radiofrequency ion traps, electric fields are produced by applying time-varying potentials between machined metal electrodes. The electrode shape constitutes a boundary condition and defines the field shape. This paper presents a new approach to making ion traps in which the electrodes consist of two ceramic discs, the facing surfaces of which are lithographically imprinted with sets of concentric metal rings and overlaid with a resistive material. A radial potential function can be applied to the resistive material such that the potential between the plates is quadrupolar, and ions are trapped between the plates. The electric field is independent of geometry and can be optimized electronically. The trap can produce any trapping field geometry, including both a toroidal trapping geometry and the traditional Paul-trap field. Dimensionally smaller ion trajectories, as would be produced in a miniaturized ion trap, can be achieved by increasing the potential gradient on the resistive material and operating the trap at higher frequency, rather than by making any physical changes to the trap or the electrodes. Obstacles to miniaturization of ion traps, such as fabrication tolerances, surface smoothness, electrode alignment, limited access for ionization or ion injection, and small trapping volume are addressed using this design.

We have performed detailed SIMION simulations of ion behavior in micrometer-sized cylindrical ion traps (r0 = 1 μm). Simulations examined the effects of ion and neutral temperature, the pressure and nature of cooling gas, ion mass, trap voltage and frequency, space-charge, fabrication defects, and other parameters on the ability of micrometer-sized traps to store ions. At this size scale voltage and power limitations constrain trap operation to frequencies about 1 GHz and rf amplitudes of tens of volts. Correspondingly, the pseudopotential well depth of traps is shallow, and thermal energies contribute significantly to ion losses. Trapping efficiency falls off gradually as qz approaches 0.908, possibly complicating mass-selective trapping, ejection, or quantitation. Coulombic repulsion caused by multiple ions in a small-volume results in a trapping limit of a single ion per trap. If multiple ions are produced in a trap, all but one ion are ejected within a few microseconds. The remaining ion tends to have favorable trapping parameters and a lifetime about hundreds of microseconds; however, this lifetime is significantly shorter than it would have been in the absence of space-charge. Typical microfabrication defects affect ion trapping only minimally. We recently reported (IJMS 2004, 236, 91–104) on the construction of a massively parallel array of ion traps with dimensions of r0 = 1 μm. The relationship of the simulations to the expected performance of the microfabricated array is discussed.

In radiofrequency ion traps, electric fields are produced by applying time-varying potentials between machined metal electrodes. The electrode shape constitutes a boundary condition and defines the field shape. This paper presents a new approach to making ion traps in which the electrodes consist of two ceramic discs, the facing surfaces of which are lithographically imprinted with sets of concentric metal rings and overlaid with a resistive material. A radial potential function can be applied to the resistive material such that the potential between the plates is quadrupolar, and ions are trapped between the plates. The electric field is independent of geometry and can be optimized electronically. The trap can produce any trapping field geometry, including both a toroidal trapping geometry and the traditional Paul-trap field. Dimensionally smaller ion trajectories, as would be produced in a miniaturized ion trap, can be achieved by increasing the potential gradient on the resistive material and operating the trap at higher frequency, rather than by making any physical changes to the trap or the electrodes. Obstacles to miniaturization of ion traps, such as fabrication tolerances, surface smoothness, electrode alignment, limited access for ionization or ion injection, and small trapping volume are addressed using this design.Radiofrequency ion traps made using pairs of planar resistive electrodes show promise for miniaturization and field optimization.Download high-res image (138KB)Download full-size image

Microparticle impacts are an important solar system process, and laboratory experiments are essential to understanding both microcratering and the results from in situ cosmic dust analyzers. However, current dust accelerators can only use conductive projectiles, limiting projectile types and possibly complicating studies of microparticle impact chemistry. We present a charging method that eliminates the need for conductive projectiles by using electrospray, instead of contact charging, to electrically charge microparticles. Using this novel application of electrospray, charged microparticles of quartz, quartz–ice aggregate, and methanol–water ice have been produced and observed. These experiments also demonstrate that the quartz surface can be protonated under non-equilibrium electrospray conditions, implying that the quartz surface may have a point of zero charge. Although coupling an electrospray source to a dust accelerator presents challenges, electrospray charging of minerals, mineral–ice aggregates, and astrophysical ices may enable experiments with projectiles that more closely resemble actual solar system materials.Highlights► Bare, uncoated minerals and ices can be charged using electrospray. ► Electrospray may form the basis of a new dust source for dust accelerators. ► An electrospray-based dust source would open new avenues for experimentation. ► Possible experiments include microparticle impacts with ice and mineral–ice projectiles.