Determination of Methyl- and Inorganic Mercury in Fish Using Focused Microwave Digestion Followed by Cu++ Addition, Sodium Tetraethylborate Derivatization, n-Heptane Extraction, and Gas Chromatography-Mass Spectrometry
SYR-SONG CHEN1,2, SHIN-SHOU CHOU1 AND DENG-FWU HWANG2*
1.Bureau of Food and Drug Analysis, Department of Health, Executive Yuan, 161-2 Kunyang St., Nangang District, Taipei City 115, Taiwan, R.O.C.
2.Department of Food Science, National Taiwan Ocean University, 2 Beining Rd., Jhongjheng District, Keelung City 202, Taiwan, R.O.C.
(Received: October 9, 2003; Accepted: April 5, 2004)
ABSTRACT
The analytical procedure for analysis of methyl- and inorganic mercury in fish was developed in this study. It involved microwave-assisted digestion with alkaline solution (tetra methyl ammonium hydroxide), addition of Cu++, aqueous-phase derivatization of mercury species with sodium tetraethylborate, and subsequent extraction with n-heptane. The various mercury derivatives were desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by electron impact mass spectrometry. Optimum conditions allowed the sample throughout to be controlled by the instrumental analysis time (about 8 min per sample) but not by the sample preparation step. At the irradiation power of 15-30, 45, and 60-75 W, sample heating times were only 3.5, 2.5, and 1.5 min, respectively. The recoveries of mercury species were 92.3?6.1% and 93.6?5.5% for methyl- and inorganic mercury, respectively. The proposed method was finally validated by the analysis of three biological certified reference materials (BCR CRM 464 tuna fish, NRC DORM-2 dogfish muscle, and NRC DOLT-2 dogfish liver).
Key words: methylmercury, inorganic mercury, microwave-assisted digestion, ethylation, GC-MS, fish