Talanta 62 (2004) 437–443 On-line liquid–liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters Aristidis N. Anthemidis ∗ , George A. Zachariadis, Charalampos G. Farastelis, John A. Stratis Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, Thessaloniki 54124, Greece Received 27 May 2003; received in revised form 10 July 2003; accepted 23 July 2003 Abstract A robust flow injection (FI) on-line liquid–liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the gl -1 level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 l loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h -1 , the enhancement factor was 155, the detection limit was 0.02 gl -1 , the relative standard deviation was 3.2% at 2.0 gl -1 Cd concentration level and the calibration curve was linear over the concentration range 0.06–6.0 gl -1 . The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples. © 2003 Elsevier B.V. All rights reserved. Keywords: Cadmium; Flow injection; Liquid–liquid extraction; Atomic absorption spectrometry; Phase separator 1. Introduction Cadmium is a highly toxic and one of the most dangerous trace elements. Because of its extremely low concentration in environmental or biological samples with usually compli- cated matrices, preconcentration and separation techniques are often required. Flame atomic absorption spectrometry (FAAS) is the most popular used technique for metals determination, but there are many limitations to determine traces of analyte in environmental samples due to insufficient sensitivity or, in some sample types, matrix interferences. Although the most extensively studied and widely applied preconcentra- tion and/or matrix elimination technique is the liquid–liquid ∗ Corresponding author. Tel.: +30-2310997707; fax: +30-2310997719. E-mail address: anthemid@chem.auth.gr (A.N. Anthemidis). extraction (LLE) [1], this procedure being operated in batch mode is time consuming, tedious, laborious and hence, potentially prone to sample contamination when ultra-trace determinations are required. The implementa- tion of liquid–liquid extraction technique in continuous mode coupled to atomic spectrometry instruments elimi- nates many of these drawbacks and contributes advantages inherent in automatic methods of analysis [2]. Since the introduction of flow injection liquid–liquid ex- traction (FI-LLE) as a mean for analyte preconcentration in flame atomic absorption spectrometry (FAAS) by Nord and Karlberg [3,4], the number of contributions in this field was rather few compared to other on-line preconcentration sys- tems [5]. This is due to the limited range of flow rate ra- tios of aqueous to organic phase of the segmented stream that on-line phase separators can handle and, in addition, the insufficient stability, versatility and robustness of them. 0039-9140/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2003.07.019