COUPLED IN-SITU ELECTRODEPOSITION-ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY - A NEW APPROACH IN QUANTITATIVE MATRIX FREE ANALYSIS

A new approach for in situ matrix elimination in electrothermal atomic absorption spectroscopy (ETAAS) is described. In an initial electrode position step (possible by use of a Pt/Ir delivery tube on the autosam pler) the furnace is coated with about 0.25 mu g Pd. Quantitative depo sition of metallic analytes onto this renewable substrate is achieved from 25-40 mu l samples by electrolysis for 60 s at 3.5-5.0 V (35-45 m A). Reprogramming of the autosampler to remove spent electrolyte after the electrolyses and to provide a rinse cycle facilitates removal of >99.5% of a 0.5 M NaCl matrix prior to atomization. It is proposed tha t the analyte is bound onto the metallic modifier, rather than encapsu lated within it. Binding of the analyte with Pd significantly increase s the appearance temperature for Cd and Pb. The ashing loss for these analytes deposited onto Pd from a Cl- matrix is observed above 900 deg rees C and 1300 degrees C, respectively. This stabilization facilitate s separation of the residual NaCl matrix before atomization. It has be en established for Cd that sensitivity of the determination remains co nstant for matrices as diverse as 1% HNO3, 0.5 M NaCl and sea water.