Q1(g). Generation of the argon plasma in ICP–MS

Answer in brief

Argon in a quartz torch is seeded with electrons by a Tesla spark; the RF coil's oscillating magnetic field drives electrons and ions whose collisions heat the gas to 6000–10 000 K.

Key points

• Torch: three concentric quartz tubes carrying argon – outer (plasma, coolant) gas tangentially, auxiliary gas, and central nebuliser gas with the sample aerosol.
• A water-cooled induction coil fed by a radio-frequency generator (27.12 or 40.68 MHz, 1–2 kW) gives an oscillating magnetic field.
• Ignition: a spark from a Tesla coil seeds the argon with electrons and ions.
• Charges move in closed circular paths (eddy current); collisions give ohmic heating and more ionisation – a self-sustaining, electrodeless plasma.
• About 10 000 K in the core, 6000–8000 K in the central channel; in ICP–MS ions pass through sampler and skimmer cones into vacuum.