An ambient detection system for visualization of charged particles generated with ionization methods at atmospheric pressure.

Rationale: With the current state-of-the-art detection of ions only taking place under vacuum conditions, active pixel detectors that operate under ambient conditions are of particular interest. These detectors are ideally suited to study and characterize the charge distributions generated by ambient ionization sources.

Methods: The direct imaging capabilities of the active pixel detector are used to investigate the spatial distributions of charged droplets generated by three ionization sources, named electrospray ionization (ESI), paper spray ionization (PSI) and surface acoustic wave nebulization (SAWN).

Hand-held portable desorption atmospheric pressure chemical ionization ion source for in situ analysis of nitroaromatic explosives.

A novel, lightweight (0.6 kg), solvent- and gas-cylinder-free, hand-held ion source based on desorption atmospheric pressure chemical ionization has been developed and deployed for the analysis of nitroaromatic explosives on surfaces in open air, offering portability for in-field analysis. A small, inexpensive, rechargeable lithium polymer battery was used to power the custom-designed circuitry within the device, which generates up to ±5 kV dc voltage to ignite a corona discharge plasma in air for up to 12 h of continuous operation, and allowing positive- and negative-ion mass spectrometry.

Direct ion imaging approach for investigation of ion dynamics in multipole ion guides.

A key requirement of electrospray ionization (ESI) and other techniques facilitating ionization at elevated pressures is the efficient transport of free gas-phase ions into the high vacuum region of the mass spectrometer. Radio frequency (RF) multipole ion guides that allow for collisional cooling are one of the most popular means of achieving this. However, their performance is highly dependent on several experimental factors, including pressure and various electrode potentials along the ion path.

A micropixelated ion-imaging detector for mass resolution enhancement of a QMS instrument.

An in-vacuum position-sensitive micropixelated detector (Timepix) is used to investigate the time-dependent spatial distribution of different charge state (and hence different mass-to-charge (m/z)) ions exiting an electrospray ionization (ESI)-based quadrupole mass spectrometer (QMS) instrument. Ion images obtained from the Timepix detector provide a detailed insight into the positions of stable and unstable ions of the mass peak as they exit the QMS. With the help of image processing algorithms and by selecting areas on the ion images where more stable ions impact the detector, an improvement in mass resolution by a factor of 5 was obtained for certain operating conditions.

Experimental investigation of the 2D ion beam profile generated by an ESI octopole-QMS system.

In this paper, we have employed an ion imaging approach to investigate the behavior of ions exiting from a quadrupole mass spectrometer (QMS) system that employs a radio frequency octopole ion guide before the QMS. An in-vacuum active pixel detector (Timepix) is employed at the exit of the QMS to image the ion patterns. The detector assembly simultaneously records the ion impact position and number of ions per pixel in every measurement frame.

Quadrupole mass filter: design and performance for operation in stability zone 3.

The predicted performance of a quadrupole mass filter (QMF) operating in Mathieu stability zone 3 is described in detail using computer simulations. The investigation considers the factors that limit the ultimate maximum resolution (Rmax) and percentage transmission (%Tx), which can be obtained for a given QMF for a particular scan line of operation. The performance curve (i.

Mapping the stability diagram of a quadrupole mass spectrometer with a static transverse magnetic field applied.

Previous experimental and theoretical work identified that the application of a static magnetic (B) field can improve the resolution of a quadrupole mass spectrometer (QMS) and this simple method of performance enhancement offers advantages for field deployment. Presented here are further data showing the effect of the transverse magnetic field upon the QMS performance. For the first time, the asymmetry in QMS operation with B x and B y is considered and explained in terms of operation in the fourth quadrant of the stability diagram.

A method of computing accurate 3D fields of a quadrupole mass filter and their use for prediction of filter behavior.

A method is described that enables the three-dimensional fields of a simple quadrupole mass filter (QMF) to be determined to a high accuracy. The technique produces accurate field values in the fringe field region as well as in the center of the filter. Using fields obtained typical filter performance is determined and shown to differ from that predicted when fringe fields are ignored.

Factors influencing the QMF resolution for operation in stability zones 1 and 3.

This study uses a computer model to simulate a quadrupole mass filter (QMF) instrument under different operating conditions for Mathieu stability zones 1 and 3. The investigation considers the factors that limit the maximum resolution (R(max)), which can be obtained for a given QMF for a particular value of scan line. Previously, QMF resolution (R) has been found to be dependent on number (N) of radio frequency (rf) cycles experienced by the ions in the mass filter, according to R = N(n)/K, where n and K are the constants.

QMS in the third stability zone with a transverse magnetic field applied.

We report here a study using a quadrupole mass spectrometer (QMS) in which a static magnetic field is applied transversely to the body of the mass filter operating in stability zone 3. Significant improvement in QMS performance was obtained under certain magnetic field conditions, and these have been explained in terms of our theoretical model. The theoretical approach assumed in the model is that the QMS contains hyperbolic rods as electrodes and that the magnetic field acts over the full length of the mass filter assembly.

Effect of an axial magnetic field on the performance of a quadrupole mass spectrometer.

We consider the case of a quadrupole mass spectrometer (QMS) in which a static magnetic field is applied axially in the z-direction along the length of the mass filter. The theoretical approach assumed in the model is that the QMS contains hyperbolic rods as electrodes and that the magnetic field acts over the full length of the mass filter assembly. Initial experimental results with argon and helium for a low-resolution instrument confirm the predicted theoretical trends.