Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab Analytical note Speciation of mercury in water and freshwater fish samples using two-step hollow fiber liquid phase microextraction with electrothermal atomic absorption spectrometry Arnon Thongsaw, Ratana Sananmuang, Yuthapong Udnan, Gareth M. Ross, Wipharat Chuachuad Chaiyasith ⁎ Department of Chemistry, Research Center for Academic Excellence in Petroleum, Petrochemical and Advanced Materials, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand ARTICLE INFO Keywords: HF-LPME ETAAS Speciation Mercury Fish ABSTRACT A novel method for trace inorganic mercury (Hg 2+ ) and methylmercury (MeHg) speciation was developed utilizing two-step hollow fiber liquid phase microextraction (two-step HF-LPME) procedures with two/three phases combined with electrothermal atomic absorption spectrometry (ETAAS). This allowed for consecutive determination of MeHg and Hg 2+ in water and fish samples. MeHg was firstly extracted into a polypropylene hollow fiber containing toluene by HF(3)-LPME, Na 2 S 2 O 3 was then injected inside the fiber lumen as an acceptor phase to trap the analyte, while Hg 2+ still existed in the aqueous solution. For Hg 2+ determination, HF(2)-LPME procedure was subsequently applied after Hg 2+ was chelated with diethyldithiocarbamate (DDTC) and then Hg 2+ -DDTC was extracted using 1-octanol. The key parameters and ETAAS profiles were investigated and op- timized. This method was then applied to mercury speciation in several real-world samples and the recoveries of these samples including a standard reference material (SRM-1566b). This led to LODs of 0.14 and 0.06 μgL -1 with 2.3 and 3.7% RSD (n = 6) achieved with enrichment factors of 103 and 95 for Hg 2+ and MeHg, respec- tively. The developed method was then evaluated and compared to other analytical techniques for mercury determination in water and fish samples. 1. Introduction Ecological contaminants are one of the main concerns effecting the environment and human health. Toxic metals rank highly in the major contaminant categories, with mercury being among the most toxic metals [1,2]. However, the toxicity of mercury normally depends on its chemical species. The most common mercury species found in biolo- gical samples are inorganic mercury (Hg 2+ ) and organic mercury (methylmercury or MeHg). These two mercury species are responsible for the vast majority of present anthropogenic mercury contamination in the environment. Hg 2+ can be readily converted into MeHg by me- thylation processes of mercuric derivatives by bacteria [3]. These or- ganometallic species are neurotoxic, cause blockage of enzyme binding sites, obstructs protein synthesis, and impedes thymidine incorporation into DNA [4]. Both inorganic and organic mercury tend to accumulate in sediments and biota, particularly fish and mollusks. MeHg exhibits a much larger tendency for biomagnification in the food chain, with the tissue of fish being of particular concern [5]. Consequently, sensitive, rapid, and inexpensive analytical techniques for the determination of mercury species in biological samples are of significant importance. The World Health Organization (WHO) have restricted the maximum allowed limits for mercury in drinking water to 1.0 μgL -1 [6], and the European Commission Regulation (1881/2006/ EC) has set the maximum recommended mercury concentration in the range of 0.5–1.0 mg kg -1 of fresh weight in fish muscle and other fishery products [7]. Several non-chromatographic analytical techniques coupled with atomic spectroscopic techniques including flame atomic absorption spectrometry (FAAS) [8], cold vapor atomic absorption spectrometry (CVAAS) [9,10], cold vapor fluorescence absorption spectrometry (CVAFS) [11,12] inductively coupled plasma (ICP) [13,14], and elec- trothermal atomic absorption spectrometry (ETAAS) [15,16] have been applied to the determination of mercury in various matrixes. Among the mentioned techniques, ETAAS is one of most sensitive and accurate analytical techniques, which uses low sample volumes (5–20 μL) and the complete matrix removal in the pyrolysis step [17]. However, the https://doi.org/10.1016/j.sab.2018.12.012 Received 1 August 2018; Received in revised form 12 December 2018; Accepted 27 December 2018 ⁎ Corresponding author. E-mail address: wipharatc@nu.ac.th (W.C. Chaiyasith). Spectrochimica Acta Part B 152 (2019) 102–108 Available online 30 December 2018 0584-8547/ © 2018 Elsevier B.V. All rights reserved. T