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. V arious acids (hydrochloric, nitric, sulphuric and perchloric) and tria mmonium citrate (TAG) were added to in the diluted samples to prevent the hydrolysis of the host material. Thermal pretreatment and atomizat ion curves of chromium indicated that the optimal pretreatment and ato mization temperatures were increased on the addition of oxo acids in t he order HNO3, H2SO4 and HClO4. As no retention of chromium in the sub sequent measurements (memory signal) was observed in the presence of t he matrix of concern, a negligible formation of chromium carbide under this condition was concluded. The peak height signals of chromium wer e significantly increased by the Bi2TeO5 matrix in the presence of HNO 3, H2SO4, and HCl-TAC, whereas the change was almost negligible for in tegrated absorbance up to 10(-2) mol l(-1) matrix concentration. The u se 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 c ondition) for the evaluation of peak height signals, which ensured suf ficient sensitivity for the present analytical task. The relative stan dard deviation (RSD) values of peak height and integrated absorbance m easurements were typically 4.2% and 3.9%, respectively. In the presenc e 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 an d 0.4 mu g l(-1), were found for peak height and for integrated absorb ance measurements, respectively. These LOD data correspond to 3.2 and 12.8 ng g(-1) (ppb) Cr in the solid samples. The calibration curves we re linear up to 20 mu g 1(-1). The RSD values of the crystal samples m easured in the 10-(5)-10(-2) mol Cr mol(-1) Bi(2)TeO5 concentration ra nge were between 2.5 and 6.1%. (C) 1997 Elsevier Science B.V.