Investigations on the determination of chromium dopant in bismuth tellurite single crystals by graphite furnace atomic absorption spectrometry

A fast dissolution of bismuth tellurite (Bi2TeO5) single crystals was performed in 40-fold molar excess of concentrated hydrochloric acid. Various acids (hydrochloric, nitric, sulphuric and perchloric) and triammonium citrate (TAG) were added to in the diluted samples to prevent the hydrolysis of the host material. Thermal pretreatment and atomization curves of chromium indicated that the optimal pretreatment and atomization temperatures were increased on the addition of oxo acids in the order HNO3, H2SO4 and HClO4. As no retention of chromium in the subsequent measurements (memory signal) was observed in the presence of the matrix of concern, a negligible formation of chromium carbide under this condition was concluded. The peak height signals of chromium were significantly increased by the Bi2TeO5 matrix in the presence of HNO3, H2SO4, and HCl-TAC, whereas the change was almost negligible for integrated absorbance up to 10(-2) mol l(-1) matrix concentration. The use of mini-flow of the internal argon gas (40 cm(3) min(-1)) resulted in a lowered interference (tailing) effect (compared to the gas-stop condition) for the evaluation of peak height signals, which ensured sufficient sensitivity for the present analytical task. The relative standard deviation (RSD) values of peak height and integrated absorbance measurements were typically 4.2% and 3.9%, respectively. In the presence of sample matrix and TAC additive, the characteristic mass values of 0.9 pg and 5.4 pg Cr, and the limit of detection (LOD) data of 0.1 and 0.4 mu g l(-1), were found for peak height and for integrated absorbance measurements, respectively. These LOD data correspond to 3.2 and 12.8 ng g(-1) (ppb) Cr in the solid samples. The calibration curves were linear up to 20 mu g 1(-1). The RSD values of the crystal samples measured in the 10-(5)-10(-2) mol Cr mol(-1) Bi(2)TeO5 concentration range were between 2.5 and 6.1%. (C) 1997 Elsevier Science B.V.