Electrothermal atomic absorption spectrometry with ballast in a rapidly heated graphite furnace: determination of lead and cadmium in seawater

The processes of Pb and Cd atomization in seawater samples in a rapidly heated (heating rate of 10 °C/msec) graphite furnace with ballast are studied. A method for determination of Pb and Cd in seawater samples using a Zeeman electrothermal atomic absorption (ETAA) spectrometer with tantalum ballast in a rapidly heated graphite furnace without preliminary sample preparation and/or addition of chemical modifiers is developed. The experiments were performed using seawater samples from the Baltic and Black Seas and a model seawater solution with a salinity of 35 g/liter. When the graphite furnace is heated, sample vapors condense on the relatively cold ballast, and then the sample repeatedly evaporates (re-evaporates) from the ballast, when it is heated by the radiation of the furnace walls, into a heated analytical cell. The shift of the atomization process to the region of steady-state and high furnace temperature and the decrease of background absorption during atomization help to decrease the chemical and matrix spectral effects on the analytical signal. To compensate the systematic error of element determination, the standard addition method adapted to the spectrometer conversion function was used. The analytical and metrological characteristics of the technique were established: characteristic masses of Pb — 2.2 pg, Cd — 0.17 pg and characteristic concentrations of Pb — 0.44 μg/liter, Cd — 0.034 μg/liter, detection limits of Pb — 0.20 μg/liter, Cd — 0.02 μg/liter, determination limits of Pb — 0.50 μg/liter, Cd — 0.05 μg/liter, random and systematic components of the error of determination of elements in seawater samples are no more than 10%.