NOBLE-METALS AS PERMANENT MODIFIERS FOR THE DETERMINATION OF MERCURY BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

Palladium, gold, rhodium and iridium have been investigated as chemica l modifiers for mercury determination by ETAAS. The gold/rhodium mixtu re and palladium alone, thermally reduced in the graphite tube, and al so electrodeposited palladium give the best analytical performance. Un der those conditions a characteristic mass of 110 pg is obtained for m ercury. The amount and the reduction temperature of the modifier, toge ther with the pyrolysis, atomization and cleaning temperatures for mer cury have been optimized in order to find best conditions for permanen t modification. Experimental conditions for palladium and rhodium afte r thermal and electrodeposition as a permanent modifier have also been optimized. It is shown that thermally deposited palladium can serve f or about 50 firings when the maximum temperature does not exceed 1800 degrees C. The tubes pretreated with a thermally deposited gold/rhodiu m mixture or electrodeposited palladium exhibit extended analytical li fetime (up to 500 firings without loss of sensitivity) even when tubes are heated up to 2000 degrees C.