ONLINE PRECONCENTRATION OF NICKEL BY CARBONYL VAPORIZATION WITH FLOW-INJECTION AND CONTINUOUS-FLOW SYSTEMS IN COMBINATION WITH SENSITIVE DETERMINATION BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A sensitive method is described for the on-line determination and preconcentration of nickel using the coupling of a flow system (continuous flow and flow injection) with transversely heated electrothermal atomic absorption spectrometry. The method is based on the volatilization of nickel as nickel tetracarbonyl and its trapping on a graphite surface. The carbonyl generation is optimized by using a simple carbon monoxide generator together with sodium tetrahydroborate(III) as reagent for the formation of pure metallic nickel. The carbonyl trapping in a graphite electrothermal atomizer is also optimized. The characteristic concentration was 0.13 mu g l(-1) for an absorption of 0.0044 and the detection limit was 0.18 mu g l(-1) both for 500 mu l sample volumes. The continuous mode allows detection limits lower than 0.01 mu g l(-1). The relative process standard deviation of this method was lower than 3%. Further examinations demonstrate the influence of heavy metals on the determination of nickel which results in the necessity of using the standard additions method to obtain. reliable data. Finally, the measurement of the standard and certified reference materials 'Trace Elements in Water' (NIST SRM 1643 c) and 'Rye Grass' (BCR CRM 281), respectively, demonstrates the efficiency of the method.