Ion motion

The motion of charged particles is an important topic in many fields of science and engineering. Modern high performance analytical methods, like mass spectrometry (MS) and ion mobility spectrometry (IMS), are based on the separation of moving molecular ions.

Therefore, to analyze substance samples with MS or IMS, the neutral substances have to be ionized in the first place.

Today in routine analytics, ionization is mostly performed by atmospheric pressure ionization (API) methods, which allow the hyphenation of MS and IMS with pre-separation stages, as for example liquid chromatography (LC).

Numerical simulation …

The numerical simulation of ion motion allows the model driven design of ion analytical devices. The simulation of ion trajectories under high vacuum conditions, where collisions between ions and residual bulk gas particles are negligible, has become an indispensable and widely used tool in mass analyzer design. However, the simulation of ion trajectories under high pressure conditions is far less applied .

… at atmospheric pressure

This is most probably due to the much higher complexity of ion motion at elevated pressure. Because of the high collision frequency between ions and background gas particles, ions interact extensively with the bulk gas at atmospheric pressure. Therefore, the trajectories of ions are also determined by the motion of the bulk gas (viscous effects) and by molecular and turbulent diffusion.

In addition, chemical transformations are much more relevant at high background pressures than under high vacuum conditions.

At low pressure conditions, only unimolecular chemical reactions (i.e. fragmentations) are possible, while at high pressure conditions all gas phase reactions between ions and neutrals become potentially relevant.

Reaction Simulation (RS) extension

The effects of the bulk gas on the ion trajectories in a numerical simulation are very well modeled by established collision models, e.g., the statistical diffusion simulation (SDS) method. Until recently, a generally applicable model including chemical change of ions at AP was missing.

RS is is an attempt to fill this gap. It is an extension to the widely used charged particle simulator SIMION and allows the simulation of chemical reactions of gas phase ions with a Monte Carlo approach.

In addition to the integration in SIMION, RS offers a standalone mode. In this mode, RS is able to solve simple chemical kinetics problems with the assumption of an ideal stirred reactor.

As SIMION user program, RS is written in the Lua scripting language, which allows the simple modification and adoption of RS.

To encourage the usage and development of RS we published the code under an open source license and make it available to the interested public through this portal.