Analytical Methods Rapid identification of c-irradiated food by direct solvent extraction and liquid chromatography–tandem mass spectrometric analysis of 2-dodecylcyclobutanone: Application in surveillance of irradiated food Wan Chan ⇑ , Yuran Ye, Elvis M.K. Leung Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Special Administrative Region article info Article history: Received 5 August 2013 Received in revised form 23 January 2014 Accepted 7 April 2014 Available online 15 April 2014 Keywords: Irradiated food 2-Dodecylcyclobutanone Precolumn derivatization HPLC Tandem mass spectrometry LC–MS/MS abstract 2-Dodecylcyclobutanone (2-DCB) is one of the major 2-alkylcyclobutanones (2-ACBs) that are uniquely formed when triglycerides are exposed to ionizing radiation and is being widely used as marker signature for identifying irradiated food. Current methods for 2-DCB extraction are either time-/solvent-consuming or involve the use of expensive extraction instruments. We have developed in this study an efficient extraction method for extracting 2-DCB from c-irradiated food by direct extraction using acetonitrile. In comparison with the European standard method for irradiated food identification, our method reduced the per sample organic solvent consumption from 450 to 30 mL per sample and shortened sample pro- cessing time from 8 h to 30 min. The assay combining direct acetonitrile extraction, precolumn derivati- zation with hydroxylamine, and LC–MS/MS analysis was validated with irradiated chicken as positive control, and applied in surveillance of irradiated food in Hong Kong. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Food irradiation induces the formation of reactive radicals that react with chemical components in the food generating radiolytic products such as formaldehyde, short-chain hydrocarbons, etc. (Crews, Driffield, & Thomas, 2012; Delincee, 2002). Among the radiolytic products, 2-alkylcyclobutanones (2-ACBs) are uniquely formed when triglycerides are exposed to ionizing radiation (Fig. 1)(Horvatovich, Miesch, Hasselmann, Delincee, & Marchioni, 2005; Miescha, Ndiayeb, Hasselmannb, & Marchioni, 1999). Con- tamination with 2-ACBs has been identified in a wide variety of irradiated foodstuff (Hijaz & Smith, 2010; Obana, Furuta, & Tanaka, 2005; Sin, Wong, & Yao, 2006). The uniqueness of 2-ACBs in irradiated foods rendered them marker molecules for identifying foodstuffs that were preserved using ionizing radiation (Gadgil, Smith, Hachmeister, & Kropf, 2005; Miescha et al., 1999). Currently, gas chromatography–mass spectrometry (GC–MS) analysis of 2-ACBs is being used extensively to identify irradiated food and was adopted by the European Committee for Standardiza- tion as one of the official standard methods for the identification of irradiated food (EN1785:2003, Anon, 2003). Among the 2-ACBs, 2-dodecylcyclobutanone (2-DCB, Fig. 1) from radiolysis of palmitic acid is the predominant species and is a widely used marker mol- ecule for identifying irradiated food. Though being widely used in irradiated food identification, EN1785:2003 suffers from the limitations of long sample process- ing time and large solvent consumption (Fig. 2)(Crews et al., 2012; Obana et al., 2005; Sin et al., 2006). The tedious and time-consum- ing operating procedures make it unsuitable for routine analysis. Efforts have been made to increase the extraction efficiency by replacing the Soxhlet extraction process in EN1785:2003 with supercritical fluid extraction (Horvatovich, Miesch, Hasselmann, & Marchioni, 2000; Stewart, McRoberts, Hamilton, & Graham, 2001), accelerated solvent extraction (Obana et al., 2005), and direct solvent extraction (Hijaz, Kumar, & Smith, 2010; Tewfik, 2008) which are more environmentally friendly. However, same as in the official standard method for 2-ACBs analysis, the modified sample preparation methods require extensive sample cleanup by flash column chromatography prior to GC–MS analysis. Recently, we have developed an LC–MS/MS method for the sen- sitive identification of 2-ACBs in c-irradiated food (Ye, Liu, Horvatovich, & Chan, 2013). The method entails acetonitrile extraction of 2-ACBs from the c-irradiated food, sample cleanup by solid-phase extraction (SPE), derivatization with hydroxyl- amine, and quantification by LC–MS/MS. In comparison with the http://dx.doi.org/10.1016/j.foodchem.2014.04.034 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +852 2358 7370; fax: +852 2358 1594. E-mail address: chanwan@ust.hk (W. Chan). Food Chemistry 161 (2014) 312–316 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem