Design, construction and study of a continuously fed ohmically heated reactor for powdered solid sample digestion

The design, construction and testing of an ohmically heated graphite reactor for digestion of continuously fed powdered (<100-mum diameter) solid samples are discussed. The system operates in a continuous sample feed mode with a 100% power 3-kW duty cycle. The configuration provides a means of protecting the graphite reactor from contact with air and an efficient method of cooling the electrodes. Furthermore, the design includes a simple interface between the reactor and the powder feeder as well as between the reactor and the plasma. Experiments conducted on SO-4 Soil Certified Reference Material (CRM) as well as on 1646 Estuarine Sediment CRM demonstrated that a linear relationship existed between the integrated time-dependent signal and the net sample mass fed when the reactor's output was fed directly into an inductively coupled plasma atomic emission spectrometer (ICP-AES). The comparison between the experimental and theoretical composition ratios for both CRMs led to good agreement, between 0.27% and 11%, for elements certified in both CRMs. Absolute limits of detection of the order of 6-7 ng for Al, Ca and Fe were achieved. Under normal operating conditions, the power dissipated in the reactor was found to be of the order of 2-3 kW with corresponding temperatures of similar to2400 to similar to2700 K. (C) 2004 Elsevier B.V. All rights reserved.