Spatially resolved spectroscopic measurements of CN, C2 and Al in graphite tube electrothermal atomizers under various operating conditions

Abstract

Direct, spatially resolved, spectroscopic measurements of C₂ in side-heated (spatially isothermal) and Massmann-type (spatially non-isothermal) atomizers showed that the partial pressure of gaseous carbon (pC₂) is in thermodynamic, heterogeneous equilibrium for temperatures above 2970 K. No evidence for over-equilibrium excesses of C₂ was obtained. The pCN exhibits a gradient, decreasing from the bottom to the top of the graphite tube, indicating the importance of air ingress through the injection hole. Further, the pCN is reduced by the presence of aqueous solutions, primarily close to the point of sample deposition, revealing the non-equilibrium distribution of CN in the atomizer, whereas C₂ is only marginally affected. Spatially resolved measurements of Al also indicate the importance of O₂ ingress and the sheath gas flow rate on the Al atomic absorption signals, indicating that the pO₂ largely determines the degree of Al atom formation and not the presence of gaseous, carbon-containing species.