The role of demixing effect in analyte emission enhancement by easily ionized elements in d.c. plasma

The effect of easily ionized elements (EIE) in d.c. plasma (DCP) has been modeled and experimentally investigated. The introduction of the EIEs in the U-shaped DCP decreases a ‘potential barrier’ due to an internal radial electric field, which allows the partially ionized analyte better entry into the hot plasma zone and produces enhancement of the analyte spectral emission. Compared to the equilibrium concentration, the increased electron concentration in the fringe region due to large radial gradients is accounted for in the model. By comparing model predictions to experimental data, the validity of the model is tested. The main features of the effect, the large enhancement at small addition of EIE and almost equal enhancement of ion and atom line intensities, are fairly well described by the model. The results are believed to be applicable to the inverted Y-shaped DCP. The effect in the inductively coupled plasma (ICP) has been briefly discussed from the point of view of the proposed model.