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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-[micro]m-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.

We describe a novel radio frequency ion trap mass analyzer based on toroidal trapping geometry and micro-fabrication technology. The device, called the halo ion trap, consists of two parallel ceramic plates, the facing surfaces of which are imprinted with sets of concentric ring electrodes. Radii of the imprinted rings range from 5 to 12 mm, and the spacing between the plates is 4 mm. Unlike conventional ion traps, in which hyperbolic metal electrodes establish equipotential boundary conditions, electric fields in the halo ion trap are established by applying different radio frequency potentials to each ring. The potential on each ring can be independently optimized to provide the best trapping field. The halo ion trap features an open structure, allowing easy access for in situ ionization. The toroidal geometry provides a large trapping and analyzing volume, increasing the number of ions that can be stored and reducing the effects of space-charge on mass analysis. Preliminary mass spectra show resolution (m/[DELTA]m) of 60-75 when the trap is operated at 1.9 MHz and 500 [V.sub.p-p].

The planar linear ion trap (PLIT) is a version of the two-dimensional linear quadrupole ion trap constructed using two facing dielectric substrates on which electrodes are lithographically patterned. In this article, we present a PLIT that was successfully miniaturized from a radius of 2.5 mm to a microscale radius of 800 μm (a scaling factor of 3.125). The mathematics concerning scaling an ion trap mass spectrometer are demonstrated—including the tradeoff between RF power and pseudopotential well depth. The time average power for the microscale PLIT is, at best, ~ 1/100 that of the PLIT but at a cost of potential well depth of ~ 1/10 the original. Experimental data using toluene/deuterated toluene and isobutylbenze to verify trap performance demonstrated resolutions around 1.5 Da at a pressure of 5.4 × 10−3 Torr. The microscale PLIT was shown to retain resolutions between 2.3 and 2.7 Da at pressures up to 42 × 10−3 Torr while consuming a factor of 3.38 less time average power than the unscaled PLIT.Graphical Abstract [ABSTRACT FROM AUTHOR]

The performance of miniaturized ion trap mass analyzers is limited, in part, by the accuracy with which electrodes can be fabricated and positioned relative to each other. Alignment of plates in a two-plate planar LIT is ideal to characterize misalignment effects, as it represents the simplest possible case, having only six degrees of freedom (DOF) (three translational and three rotational). High-precision motorized actuators were used to vary the alignment between the two ion trap plates in five DOFs—x, y, z, pitch, and yaw. A comparison between the experiment and previous simulations shows reasonable agreement. Pitch, or the degree to which the plates are parallel along the axial direction, has the largest and sharpest impact to resolving power, with resolving power dropping noticeably with pitch misalignment of a fraction of a degree. Lateral displacement (x) and yaw (rotation of one plate, but plates remain parallel) both have a strong impact on ion ejection efficiency, but little effect on resolving power. The effects of plate spacing (y-displacement) on both resolving power and ion ejection efficiency are attributable to higher-order terms in the trapping field. Varying the DC (axial) trapping potential can elucidate the effects where more misalignments in more than one DOF affect performance. Implications of these results for miniaturized ion traps are discussed.ᅟ [ABSTRACT FROM AUTHOR]

We present a new two-plate linear ion trap mass spectrometer that overcomes both performance-based and miniaturization-related issues with prior designs. Borosilicate glass substrates are patterned with aluminum electrodes on one side and wire-bonded to printed circuit boards. Ions are trapped in the space between two such plates. Tapered ejection slits in each glass plate eliminate issues with charge build-up within the ejection slit and with blocking of ions that are ejected at off-nominal angles. The tapered slit allows miniaturization of the trap features (electrode size, slit width) needed for further reduction of trap size while allowing the use of substrates that are still thick enough to provide ruggedness during handling, assembly, and in-field applications. Plate spacing was optimized during operation using a motorized translation stage. A scan rate of 2300 Th/s with a sample mixture of toluene and deuterated toluene (D8) and xylenes (a mixture of o-, m-, p-) showed narrowest peak widths of 0.33 Th (FWHM).ᅟ [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a method for characterizing electric field profiles of radio frequency (rf) quadrupole ion trap structures using sensors based on slab coupled optical-fiber sensor (SCOS) technology. The all-dielectric and virtually optical fiber-sized SCOS fits within the compact environment required for ion traps and is able to distinguish electric field orientation and amplitude with minimal perturbation. Measurement of the fields offers insight into the functionality of traps, which may not be obtainable solely by performing simulations. The SCOS accurately mapped the well-known field profiles within a commercially available three-dimensional quadrupole ion trap (Paul trap). The results of this test allowed the SCOS to map the more complicated fields within the coaxial ion trap with a high degree of confidence as to the accuracy of the measurement. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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 ( A/ A) component. A best resolution of 280 ( m/Δ m) 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. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

This paper compares dynamic (i.e., temporally changing) thermal gradient gas chromatography (GC) to temperature-programmed GC using a previously published stochastic transport model to simulate peak characteristics for the separation of C12-C40 hydrocarbons. All comparisons are made using chromatographic conditions that give approximately equal analyte retention times ( t R ). As shown previously, a static thermal gradient does not improve resolution ( R s ) equally for all analytes, which highlights the need for a dynamic thermal gradient. An optimal dynamic thermal gradient should result in constant analyte velocities at any instant in time for those analytes that are actively being separated (i.e., analytes that have low retention factors). The average separation temperature for each analyte is used to determine the thermal gradient profile at different times in the temperature ramp. Because many of the analytes require a similar thermal gradient profile when actively being separated, the thermal gradient profile in this study was held fixed; however, the temperature of the entire thermal gradient was raised over time. From the simulations performed in this study, optimized dynamic thermal gradient conditions are shown to improve R s by up to 13% over comparative temperature-programmed conditions, even with a perfect injection (i.e., zero injection bandwidth). In the dynamic thermal gradient simulations, all analytes showed improvements in R s along with slightly shorter t R values compared to simulations for traditional temperature-programmed conditions.

This paper compares static (i.e., temporally unchanging) thermal gradient gas chromatography (GC) to isothermal GC using a stochastic transport model to simulate peak characteristics for the separation of C12-C14 hydrocarbons resulting from variations in injection bandwidth. All comparisons are made using chromatographic conditions that give approximately equal analyte retention times so that the resolution and number of theoretical plates can be clearly compared between simulations. Simulations show that resolution can be significantly improved using a linear thermal gradient along the entire column length. This is mainly achieved by partially compensating for loss in resolution from the increase in mobile phase velocity, which approximates an ideal, basic separation. The slope of the linear thermal gradient required to maximize resolution is a function of the retention parameters, which are specific to each analyte pair; a single static, thermal gradient will not affect all analytes equally. A static, non-linear thermal gradient that creates constant analyte velocities at all column locations provides the largest observed gains in resolution. From the simulations performed in this study, optimized linear thermal gradient conditions are shown to improve the resolution by as much as 8.8% over comparative isothermal conditions, even with a perfect injection (i.e., zero initial bandwidth).

The analysis of individual biological nanoparticles has significantly advanced our understanding of fundamental biological processes but is also rapidly becoming relevant for molecular diagnostic applications in the emerging field of personalized medicine. Both optical and electrical methods for the detection and analysis of single biomolecules have been developed, but they are generally not used in concert and in suitably integrated form to allow for multimodal analysis with high throughput. Here we report on a dual-mode electrical and optical single-nanoparticle sensing device with capabilities that would not be available with each technique individually. The new method is based on an optofluidic chip with an integrated nanopore that serves as a smart gate to control the delivery of individual nanoparticles to an optical excitation region for ensemble-free optical analysis in rapid succession. We demonstrate electro-optofluidic size discrimination of fluorescent nanobeads, electro-optical detection of single fluorescently labeled influenza viruses, and the identification of single viruses within a mixture of equally sized fluorescent nanoparticles with up to 100% fidelity.

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 measurements of picosecond dynamics of individual nickel nanomagnets as a function of magnet dimension, aspect ratio, and magnetic environment. Spatial sensitivity to nanomagnet diameters as small as 125 nm is achieved by use of cavity enhancement of the magneto-optic Kerr effect (CE-MOKE). The importance of single-particle measurements without ensemble effects for extracting the size dependence of the intrinsic nanomagnet material properties is demonstrated.