Solvent bar micro-extraction: Improving hollow fiber liquid phase micro-extraction applicability in the determination of Ni in seawater samples.

During the last decade, hollow fiber liquid phase micro-extraction (HF-LPME) has become an attractive alternative in sample treatment for the analysis of trace metals in seawater. If compared with other similar methodologies, its main advantages are associated to a higher stability of the organic solution contained into the pores of the fiber, which acts as a lipophilic membrane during the extraction process. However there are some remaining problems that makes its use difficult, mostly related to the need of increasing the rate of analysis and improving portability. In this paper a novel three phase solvent bar micro-extraction (3PSBME) for the fiber device has been proposed. Its main advantage is that the 3PSBME device can be left free in the sample. This way the system is portable, and no special support is needed leading to the possibility of simultaneous extraction of several samples. In this work, multivariate central composite design of experiment has been carried out to optimize Ni pre-concentration using di-2-ethylhexyl phosphoric acid (DEHPA) as extractant and HNO3 as acceptor agent. Factors influencing extraction have been the pH in the sample and the fiber length. For seawater samples, Ni can be pre-concentrated 11 times in 140 min. The method presents RSD 9.42% and limit of detection 44 ng L(-1), using GFAAS for instrumental determination. It has been applied for determination of Ni in seawater, including a reference material CRM-403 proving its applicability.