Fast heating induced impulse halogenation of refractory sample components in electrothermal atomic absorption spectrometry by direct injection of a liquid halogenating agent

A novel electrothermal atomic absorption spectrometry (ETAAS) method was developed for the halogenation of refractory sample components (Er, Nd and Nb) of lithium niobate (LiNbO₃) and bismuth tellurite (Bi₂TeO₅) optical single crystals to overcome memory effects and carry-over. For this purpose, the cleaning step of a regular graphite furnace heating program was replaced with a halogenation cycle. In this cycle, after the graphite tube cooled to room temperature, a 20 μL aliquot of liquid carbon tetrachloride (CCl₄) was dispensed with a conventional autosampler into the graphite tube. The CCl₄ was partially dried at 80 °C under the mini-flow (40 cm³ min⁻¹) condition of the Ar internal furnace gas (IFG), then the residue was decomposed (pyrolyzed) by fast furnace heating at 1900-2100 °C under interrupted flow of the IFG. This step was followed by a clean-out stage at 2100 °C under the maximum flow of the IFG. The advantage of the present method is that it does not require any alteration to the graphite furnace gas supply system in contrast to most of the formerly introduced halogenation techniques.The effectiveness of the halogenation method was verified with the determination of Er and Nd dopants in the optical crystals. In these analyses, a sensitivity decrease was observed, which was likely due to the enhanced deterioration of the graphite tube surface. Therefore, the application of mathematical correction (resloping) of the calibration was also required. The calibration curves were linear up to 1.5 and 10 μmol L⁻¹ for Er and Nd, respectively. Characteristic masses of 18 and 241 pg and the limit of detection (LOD) values of 0.017 and 0.27 μmol L⁻¹ were found for Er and Nd, respectively. These LOD data correspond to 0.68 μmol mol⁻¹ Er and 11 μmol mol⁻¹ Nd in solid bismuth tellurite samples. The analytical results were compared with those obtained by a conventional ETAAS method and validated with X-ray fluorescence spectrometry analysis.