Investigation of a medium power radiofrequency capacitively coupled plasma and its application to high-temperature superconductor analysis via atomic emission spectrometry

Abstract

A medium power radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) with low argon consumption (0.4 l min⁻¹) was investigated to be used for the analysis of high critical temperature Bi–Sr–Ca–Cu–O and Bi(Pb)–Sr–Ca–Cu–O superconducting materials by atomic emission spectrometry. The plasma torch was operated in two geometric configurations, coaxial and coaxial–annular, with single (SRT-rf-CCP) or double ring electrodes (DRT-rf-CCP), respectively. The optimum experimental parameters (observation height, distance between ring electrodes and coupling geometry) and matrix interference of Ca and Sr were established. Under optimum operating conditions of the DRT-rf-CCP torch detection limits of 2.5–3 ng ml⁻¹ for Ca, 4.5–5 ng ml⁻¹ for Sr, 11–16.6 ng ml⁻¹ for Cu, 56–95 ng ml⁻¹ for Pb and 195–545 ng ml⁻¹ for Bi were found in the presence of Ca and Sr in the range of 0–500 μg ml⁻¹. Figures of merit of the investigated plasma torch were compared with those of ICP-AES. Each of the relevant metals from the superconducting materials could be determined successfully (the recovery levels were in the range from 97.7 ± 3.3% for Ca to 103.8 ± 3.8% for Pb and the precision between 0.8 and 3.6%). Therefore, a good agreement, based on a t-test and a two-tailed F-test, was found between the DRT-rf-CCP-AES results and those obtained by ICP-AES and given by the supplier. Overall precision of the stoichiometric coefficients by DRT-rf-CCP-AES was between 2.25–2.55%. The real stoichiometry of the superconductors obtained by DRT-rf-CCP-AES was also confirmed by the results of X-ray diffraction measurements.