Improvement of the capabilities of solid sampling ETV-ICP-OES by coupling ETV to a nebulisation/pre-evaporation system
The outlet of a solid sampling (SS) electrothermal vaporization (ETV) system was coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) through a switching tee, which was itself connected to the side arm of a sheathing device inserted between a nebulizer/spray chamber system and the ICP torch. The valve was used to evacuate the pyrolysis products during the ashing step and to direct analytes towards the ICP during the vaporisation step, so that they would merge with a pre-evaporated aerosol. The aerosol exiting the spray chamber was indeed heated by infrared heating of the sheathing device and bottom of the torch to 400 °C. This system allowed the introduction of more than twice the amount of solid sample (i.e. 13 mg instead of 5 mg) without extinguishing the plasma, as only the analyte portion actually reached the ICP. Under optimum conditions and compared to conventional SS-ETV-ICP-OES (where the ETV outlet is directly connected to the torch), improvement in sensitivity by up to 5-fold and detection limit by up to 20-fold was obtained for a range of elements, the improvement being in general larger for ionic emission lines than for atomic ones. This system also allowed an accurate but more precise (by about 2-fold on average) analysis of a soil certified reference material (CRM) using another soil CRM for external calibration and an Ar emission line for internal standardization than conventional SS-ETV-ICP-OES.