Ion Clouds in the Inductively Coupled Plasma Torch: A Closer Look through Computations

Abstract

We have computationally investigated the introduction of copper elemental particles in an inductively coupled plasma torch connected to a sampling cone, including for the first time the ionization of the sample. The sample is inserted as liquid particles, which are followed inside the entire torch, i.e., from the injector inlet up to the ionization and reaching the sampler. The spatial position of the ion clouds inside the torch as well as detailed information on the copper species fluxes at the position of the sampler orifice and the exhausts of the torch are provided. The effect of on- and off-axis injection is studied. We clearly show that the ion clouds of on-axis injected material are located closer to the sampler with less radial diffusion. This guarantees a higher transport efficiency through the sampler cone. Moreover, our model reveals the optimum ranges of applied power and flow rates, which ensure the proper position of ion clouds inside the torch, i.e., close enough to the sampler to increase the fraction that can enter the mass spectrometer and with minimum loss of material toward the exhausts as well as a sufficiently high plasma temperature for efficient ionization.

The 2017 Plasma Roadmap: Low temperature plasma science and technology

“…To overcome matrix interferences in ICP analyses, there is an ongoing effort to fundamentally characterize the ICP and the events that lead to signal generation [144]. Further, because RF supplies are bulky and inefficient and argon flows are substanti al and costly, alternatives to the ICP are being sought.…”

Inductively coupled plasma-mass spectrometry: insights through computer modeling

“…The latter model served as the basis for the further modeling work performed within our group PLASMANT. [127][128][129][130][131][132][133] Indeed, in a follow-up study, we described the ICP torch connected to a MS sampler cone, considering the large pressure drop from upstream to downstream (i.e. 1 atm to 1 torr).…”

“…131 Recently, we extended the model, to incorporate the behavior of analyte material. In first instance, we focused on elemental particles, as relevant for LA-ICP-MS. [132][133] The inserted particles were followed throughout the ICP, up to the evaporation step. 132 Finally, we also included ionization of the elemental particles, taking Cu as a case study.…”

“…132 Finally, we also included ionization of the elemental particles, taking Cu as a case study. 133 This model allows us to trace the particles, and to determine their position, their phase (liquid, vapor or ionized), velocity and temperature, both in the ICP torch and at the sampler orifice. Thus, we can determine the shape and position of the ion clouds, originating from either the Ar flow or the inserted sample material, which is of interest for both OES and MS studies.…”

Optimization of plasma sampling depth and aerosol gas flow rates for single particle inductively coupled plasma mass spectrometry analysis

“…For optimum ICP-MS signal, the direction and rate of the aerosol gas flow is also very important, as it has been recently shown by Aghaei and Bogaerts in their solution droplet-evaporation simulation studies. It was found that the exact uniaxial positioning of the aerosol flow within the injector tube (on-axis) with the sampling orifice is crucial for an efficient analyte sampling through the sampling orifice [43]. Experiments and simulations carried out by Spencer et al [44,45] also conclusively showed that any deviation of the analyte flow from the central axis has a negative effect on the transmission between the first and second vacuum stages.…”