Effect of an inductively coupled plasma mass spectrometry sampler interface on electron temperature, electron number density, gas-kinetic temperature and analyte emission intensity upstream in the plasma

Abstract

Thomson scattering, Rayleigh scattering and line-of-sight emission intensities of Ca ion and Sr ion from the inductively coupled plasma were measured in the presence and in the absence of an inductively coupled plasma mass spectrometry sampler interface. When present, the sampler interface was located 13 mm above the load coil (ALC); optical measurements were made 6, 7 and 8 mm ALC. The experimental results suggest that both the electron temperature ( T e) and gas-kinetic temperature ( T g) dropped in the presence of the sampler interface, with the change in T g seemingly greater than that in T e, suggesting a faster cooling process for the heavy particles. In contrast, electron number density ( n e) seemed to be generally increased in the outer regions of the discharge but went down in the central channel, a reflection that n e is possibly dominated by ambipolar diffusion which becomes less efficient as T e drops. Assuming these results, the plasma decays more gradually ALC and deviates from local thermodynamic equilibrium even more significantly in the presence of the sampler interface. Analyte line emission intensity was either depressed or enhanced in the presence of the interface, depending on the element being observed and the operating conditions. In addition, the change in emission intensity caused by the sampler interface became much more dramatic when a matrix element, such as Li or Zn, was introduced.