OnLine Coupling of a Flow Injection System to TS‐FF‐AAS for Preconcentration and Determination of Lead in Water and Vegetables

Abstract

An online solid phase preconcentration system coupled to thermospray flame furnace atomic absorption spectrometry (TS‐FF‐AAS) for Pb(II) ions determination is described. In the preconcentration system, Pb(II) ions complexed with ammonium O,O‐diethyl‐dithiophosphate (DDTP) in an acidic medium are preconcentrated as a neutral complex onto 20 mg of polyurethane foam (PUF) packed into a mini‐column. The complex retained in the PUF is then released to TS‐FF‐AAS by using an 80% (v/v) ethanol solution. Chemical and flow variables associated with the preconcentration, such as the pH dependence of the Pb‐DDTP complex, the DDTP concentration, and preconcentration and elution flow rates were optimized by the univariate method. The best sample pH value and DDTP concentration achieved are 2.0 and 0.5% (w/v), respectively, while the best preconcentration and elution flow rates are 2.4 and 1.0 mL min⁻¹, respectively. Under the optimized conditions, the present method, which is operated in volume mode (only 2 mL), makes possible the determination of Pb(II) ions within a linear range from 5.2 to 300.0 µg L⁻¹ with a detection limit of 1.5 µg L⁻¹ and analytical frequency of 16 h⁻¹. The precision (n=10) assessed as relative standard deviation (RSD) is, respectively, 7.3 and 4.8% for 6 and 200 µg L⁻¹ solutions of Pb(II). The preconcentration system provides an enrichment factor of 6.4 and consumption index of 310 µL. Hence, the coupling of the preconcentration system to TS‐FF‐AAS is proven to be an efficient strategy to enhance TS‐FF‐AAS detectability. The applicability of the method was verified by analyses of spiked water samples as well as with certified and reference vegetable materials.

Keywords:

• Flow preconcentration system
• TS‐FF‐AAS
• lead determination
• polyurethane foam

The authors are grateful to the Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP, process numbers 01/05614‐0 and 99/12124‐7) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for fellowships and financial support. The authors also thank Prof. Carol H. Collins for language assistance.