Evaluation of drying conditions of fish tissues for inorganic mercury and methylmercury speciation analysis Lucas Schmidt a , Cezar A. Bizzi a , Fabio A. Duarte b , Valderi L. Dressler a , Erico M.M. Flores a, ⁎ a Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil b Escola de Química e Alimentos, Universidade Federal do Rio Grande, 96201-900, Rio Grande, RS, Brazil abstract article info Article history: Received 18 November 2012 Received in revised form 14 December 2012 Accepted 14 December 2012 Available online 22 December 2012 Keywords: Speciation analysis Mercury Fish Drying Lyophilization Hg species conversions The influence of drying conditions on the behavior of Hg species (Hg 2+ and CH 3 Hg + ) present in fish tissues was evaluated. Drying conditions were evaluated for six fish species using air circulation drying oven in dif- ferent temperatures (50 to 175 °C) and lyophilization (0.25 mm Hg, -2 °C). Evaluation of drying step was based on losses and conversions of original Hg species after each drying condition. The extraction efficiency was determined by comparing the concentration of total Hg in digested samples (wet digestion in closed system using HNO 3 ) with extracted Hg using L-cysteine solution. Chemical vapor generation-inductively coupled plasma mass spectrometry (CVG-ICP-MS) and liquid chromatography-chemical vapor generation-inductively coupled plasma mass spectrometry (LC-CVG-ICP-MS) were used for the determination of total Hg and Hg spe- cies, respectively. The accuracy was evaluated using certified reference materials and an agreement better than 97% with certified values was obtained for CH 3 Hg + and total Hg. The relative standard deviation of the proposed method was below 5.5%. Limit of detection of 1.7 and 2.3 ng g -1 as Hg was obtained for Hg 2+ and CH 3 Hg + , respectively. Results showed that with drying temperatures above 100 °C losses and conversions of CH 3 Hg + to Hg 2+ can occur for some fish species. © 2012 Elsevier B.V. All rights reserved. 1. Introduction One of the main problems related to chemical speciation analysis is to ensure the integrity of the species throughout the analytical proce- dure. However, several steps of analytical procedure may result in changes of the chemical species, which can lead to an erroneous inter- pretation of analytical results [1–3]. Considering the analysis of specia- tion, Hg could be pointed out as one of the most studied element, as well as As, Cr, Sb, Se, Sn, among others [4–10]. As observed for other ele- ments, Hg presents some physical-chemical and toxicological charac- teristics that depends on the chemical form. Mercury can be found linked to organic groups, such as methyl, ethyl, and related compounds, where the related species are, in general, considered more toxic than el- emental Hg and even its inorganic species [11–13]. The main exposure pathway of Hg to humans is through the consumption of fish where Hg is present mainly in the methylated form. Methylmercury (CH 3 Hg + ) is efficiently adsorbed from the gastro-intestinal tract, and it passes the blood-brain and placenta bar- riers. Consequently, Hg compounds are associated to several diseases, mainly those related to central nervous system [14–17]. Hence, studies have been performed in order to check and control Hg levels and its chemical species in several kind of samples, mainly in fishes. In this sense, several sample preparation methods to speciation analysis were developed in recent decades [18,19]. Most of samples for Hg speciation analysis require a drying step, mainly biological samples. In general, dried samples are more suit- able for homogenization, analyte extraction and sample conserva- tion. Among the drying procedures commonly used in sample preparation, it can be highlighted the use of lyophilization and dry- ing oven with forced air circulation [20]. Drying performed in ovens is frequently used as a pre-treatment for most of chemical analysis. It is considered practical and relatively cheaper than other drying procedures, such as lyophilization [21]. On this aspect, lyophilization is a drying process where the sample previ- ously frozen is dried by sublimation using low temperature drying at re- duced pressure. The key steps normally involved in this process are freezing, primary drying, and secondary drying [22]. Due to the low temperatures required in this process, many methods for speciation analysis have been employed using lyophilization in order to maintain the analytes integrity [23]. Currently, most of sample preparation methods related to Hg speci- ation analysis for biological samples employs some types of drying treatment [24–26]. However, little is known about the influence of dry- ing on preservation and integrity of Hg species [27]. Furthermore, many studies were performed using dried certified reference materials (CRMs) which could not represent a “real sample”, since these materials generally exhibit higher stability, [28–30] and therefore could be more resistant to variation such as temperature. Microchemical Journal 108 (2013) 53–59 ⁎ Corresponding author. Tel./fax: +55 55 3220 9445. E-mail address: ericommf@gmail.com (E.M.M. Flores). 0026-265X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.microc.2012.12.010 Contents lists available at SciVerse ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc