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-μm 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 reactorʹs 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 ∼2400 to ∼2700 K.