Spectroscopic diagnostics of axially viewed inductively coupled plasma and microwave induced plasma coupled to photochemical vapor generation with pneumatic nebulization inside a programmable temperature spray chamber

Abstract

Both argon inductively coupled plasma (ICP) and argon microwave induced plasma (MIP) coupled to photochemical vapor generation (PCVG) and pneumatic nebulization (PN) inside a programmable temperature cyclonic spray chamber (PTSC) have been widely characterized via optical emission spectrometry. Plasma diagnostics revealed an interesting relationship between fundamental plasma parameters and PTSC temperature in the examined range of 0–60 °C which was different for the two plasmas examined. For ICP, all measured parameters including rotational temperature (T_rot), excitation temperature (T_exc), ionization temperature (T_ion) and electron number density (n_e) consequently increased (3–22%) with increasing PTSC temperature. In turn, for MIP only T_rot and T_exc for Fe showed a similar trend while the other examined parameters slightly decreased (about 15% for n_e and T_exc for Ar with increasing PTSC temperature). As a result, ICP robustness increased with increasing PTSC temperature while MIP robustness decreased. Three factors influencing changes of plasma parameters were selected and considered including water transport efficiency, carbon-related matrix effect and analyte volatility. The observed trends are consistent with analytical data obtained previously and are supported by additional investigation of the sample transport efficiency of the sampling system. Thus, partial sample evaporation at elevated PTSC temperature is finally confirmed, although saturation of the nebulizer gas with water vapor is not achieved when it exits the PTSC. Enhancements of analyte emission intensity related to PTSC heating are due to the improved plasma robustness rather than higher sample transport efficiency.