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 m odeled and experimentally investigated. The introduction of the EIEs in the U-shaped DCP decreases a 'potential barrier' due to an internal radial ele ctric held, which allows the partially ionized analyte better entry into th e hot plasma zone and produces enhancement of the analyte spectral emission . Compared to the equilibrium concentration, the increased electron concent ration in the fringe region due to large radial gradients is accounted for in the model. By comparing model predictions to experimental data, the vali dity of the model is tested. The main features of the effect, the large enh ancement at small addition of EIE and almost equal enhancement of ion and a tom line intensities, are fairly well described by the model. The results a re believed to be applicable to the inverted Y-shaped DCP. The effect in th e inductively coupled plasma (ICP) has been briefly discussed from the poin t of view of the proposed model. (C) 2000 Elsevier Science B.V. All rights reserved.