Ultrasound-assisted hollow fiber/ionic liquid-based liquid phase microextraction using an ionic liquid solvent for preconcentration of cobalt and nickel ions in urine samples prior to FAAS determination Keng-Chang Hsu, a Cheng-Fa Lee, a Yu-Ying Chao, b Chih-Chang Hung, c Po-Chih Chen, ad Chien-Hua Chiang ad and Yeou-Lih Huang * ade Ultrasound-assisted (UA) hollow fiber (HF) liquid-phase microextraction (LPME) coupled with flame atomic absorption spectrometry (FAAS) has been developed to preconcentrate and determine ultra-trace amounts of cobalt (Co) and nickel (Ni) ions in human urine. To the best of our knowledge, no previous reports have described the coupling of UA-ionic liquid (IL)-HF-LPME with an FAAS system to analyze metal ions in biological samples. In this study, the ILs 1-hexyl-3-methylimidazolium hexafluorophosphate, sodium hexafluorophosphate, and 1-(2-pyridylazo)-2-naphthol were used as extraction, ion-pairing, and chelating agents, respectively. With the assistance of an ultrasonic probe, the analyte exchange between the phases increased, and the extraction efficiency of Co and Ni ions improved significantly. The collected extraction phase was subsequently analyzed directly through FAAS. Under optimized conditions, the detection limits of Co and Ni ions were 0.09 and 0.03 mgL 1 , respectively. The precision of the analysis of Co and Ni ions was within a relative standard deviation of 10% under normal operating conditions. The ultrasonic assistance provided enrichment factors of 66 and 82 for Co and Ni ions, respectively. The recoveries of Co and Ni ions spiked in urine samples ranged from 93.8 to 104.3%. The practicality of the proposed method was demonstrated through satisfactory analyses of samples of a standard reference material and real human urine. 1. Introduction Because it can be difficult to quantify trace amounts of metal ions in biological samples, whether from complicated matrices or limited sample volumes, various sample preconcentration methods have been developed for a range of ions and samples. Among these pretreatment processes, extraction is commonly used in techniques such as solid-phase extraction (SPE), 1 solid-phase microextraction (SPME), 2,3 and liquid-phase micro- extraction (LPME). 4,5 LPME is based on the distribution of an analyte between an organic solvent and an aqueous solution. Because of the slow extraction kinetics and increasing concerns about environmentally friendly chemistry, several different external forces have been used to improve this technique, including emulsication-based LPME (EMU-LPME) and hollow ber-based LPME (HF-LPME). The rst study of HF-LPME, pre- sented by Pedersen-Bjergaard et al., 6 involved its use as a sample preparation technique. HF-LPME is a promising miniaturized pretreatment technique that has attracted considerable attention in recent years; it is one of the most effective pre-concentration methods for trace element analyses. 7–9 The HF used in this process is a single porous tube of poly- propylene that supports an aqueous extraction phase in the lumen to microextract target analytes. In general, an organic solvent is used as the aqueous extraction phase to improve the extraction efficiency (EE). Furthermore, taking advantage of their low cost, minimal solvent consumption, simple cleanup, environmental friendliness, and complete retention of the extraction liquid, HF-LPME approaches toward analyzing metal ions have been subjected to several modications and improvements. In 1997, Parthasarathy and co-workers reported a new analytical system, using HF-LPME combined with atomic absorption spectrometry, for trace metal analyses in water samples. 10 In their study, cadmium, copper, and lead ions were extracted from the samples by stirring and passage into an HF, which supported a liquid membrane comprising 1,10-didecyldiaza [18]crown-6, fatty acid, and a mixture of toluene and a Department of Medical Laboratory Science and Biotechnology, Kaohsiung Medical University, No. 100, Shih-Chuan 1st Road, Kaohsiung 807, Taiwan. E-mail: yelihu@ kmu.edu.tw; Fax: +886-7-311-3449; Tel: +886-7-312-1101 ext. 2251 b Department of Public Health, Kaohsiung Medical University, Kaohsiung, Taiwan c Research Center for Environmental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan d Department of Laboratory Medicine, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan e Department of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan Cite this: J. Anal. At. Spectrom. , 2016, 31, 2338 Received 13th May 2016 Accepted 29th September 2016 DOI: 10.1039/c6ja00183a www.rsc.org/jaas 2338 | J. Anal. At. Spectrom., 2016, 31, 2338–2345 This journal is © The Royal Society of Chemistry 2016 JAAS TECHNICAL NOTE Published on 29 September 2016. Downloaded by Kaohsiung Medical University on 10/12/2016 03:24:47. View Article Online View Journal | View Issue