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 prec oncentration of nickel using the coupling of a flow system (continuous flow and flow injection) with transversely heated electrothermal atom ic absorption spectrometry. The method is based on the volatilization of nickel as nickel tetracarbonyl and its trapping on a graphite surfa ce. The carbonyl generation is optimized by using a simple carbon mono xide generator together with sodium tetrahydroborate(III) as reagent f or the formation of pure metallic nickel. The carbonyl trapping in a g raphite 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 tha n 3%. Further examinations demonstrate the influence of heavy metals o n the determination of nickel which results in the necessity of using the standard additions method to obtain. reliable data. Finally, the m easurement of the standard and certified reference materials 'Trace El ements in Water' (NIST SRM 1643 c) and 'Rye Grass' (BCR CRM 281), resp ectively, demonstrates the efficiency of the method.