Anal. Chem. zyxwvut 1993, 65, 763-766 763 Determination of Methylmercury in Fish Samples Using GC/AA and Sodium Tetraethylborate Derivatization Ralf Fischer, Spyridon Rapsomanikis,’ and Meinrat 0. Andreae zyxwv Biogeochemistry Department, Max Planck Institute for Chemistry, zyxwv P.O. Box 3060, 6500 Mainz, Germany A rknple technlqw Is dercrlbed for the rapld determlnallon of mdhylmercwy In flsh the. Followlng rlmple d h l u t l o n In methanok KOH rolutlon, aqueous phase ethylatlon by d.rhnaUzatbnwlth NaB(C2Hs),, cryogmktrapplngon a packed chromatographic column, and GC separatlon, volatlk mercury specks are detected by atomlc abwptlon spectrometry. Absolute dotectkn llmlts are 4 pg of Hg for CHSHg+ and 75 pg of Hg for lablle Hg2+. Concentratkn detectlon llmlts for thlr opllmlzed procedure are 4 ng of Hg for CH3Hg+and 75 ng of Hg for Iablle Hg2+ per gram of pulverlzed drled flsh tkrue. Analydr of standard reference materlak demonstrates the accuracy, preclrlon, and reproduclblllty zyxwvut of the analytlcal method. INTRODUCTION As a result of human activity and biogeochemicalprocesses, mercury is cycled in the environment. Its biogeochemical pathway are continuouslybeing aeeegaed by scientistsbecause uncertainties about the strengths of the sources and the sinks and about the transformation processes still persist. Its industrial use has dwindled in recent years due to concern about mercury toxicity.’ Elevated concentrations of meth- ylmercury found in fish and birds in the late 19608 could not be correlated to methylmercury spillage or misuse.2 It was later demonstrated that mercury can be methylated in the environment and accumulate in fish. Belonging to a higher step in the food ladder, birds also accumulate methylmercury from fish in their diet.394 The pathways for the environmental methylation of mercury have been reviewed.’ A number of publications have discussed the concentration of mercury in marine waters and in fish of the equatorial Pacific5 and in fresh water lakes and fish in the western U.S.A.6 The process of methylation and elevated methylmercury concentrations in freshwater fish has also been associated with lake acidi- fication through acid rain.’ Many aspects of mercury biogeochemistryhave been discussed at a recent conference.8 Today, it is necessary to speciate and hence distinguish between organic and inorganic forms of mercury because, generally, methylmercury is more toxic than inorganic mercury. Speciation also assists in understanding the bio- geochemical cycling of mercury and the identification of the “environmental compartments” where transformations of the mercury species can take place. * To whom correspondence should be addressed. (1) Craig, P. J. Organometallic Compounds in the Enuironment; (2) West%, G. Acta Chem. Scand. 1966,20, 2131-2138. (3) Jensen, S.; Jernelov, A. Nature (London) 1968,223, 753-754. (4) Wood, J. M.; Kennedy, F. S.; Rosen, C. G. Nature (London) 1968, (5) Mason, R. P.; Fitzgerald, W. F. Nature (London) 1990,347,457- (6) Gill, G. A,; Bruland, K. W. Enuiron. Sci. Technol. 1990,24,1392- (7) Rallof, J. Sci. News 1991, 139, 152-156. (8) Lindqvist, 0. Water, Air Soil Pollut. 1991, 56. Longman: Harlow, U. K., 1986. 220, 173-175. 459. 1400. 0003-2700/93/0365-0763$04.00/0 Methylmercury in organic, aqueous, or sediment samples is usually determined after extraction into organic solvent, stripping into aqueous solution for cleanup purposes, reex- traction into an organic solvent, and chromatography.+13 Electron capture detection is usually employed in gas chromatography (absolute detection limits ca. 50-100 pg). This necessitates the use of extremely pure solvents and tedious cleanup procedures to eliminate electron-capturing species coeluting with the organomercury compounds.14 Other techniques for the detection and speciationof mercury- containing compounds in environmental samples involve the coupling of chromatography (gas or liquid) with atomic spectrometry.15 These allow the avoidance of extensive cleanup procedures since the atomic detectors are element specific and they effect unambiguous identification and determination of the mercury species. However, the chro- matographic separation of methylmercury compounds is still fraught with difficulty because polar CH,Hg+ and Hg2+have to be cochromatographed with nonpolar (CH&Hg or HP. Hence organic mercury species are analyzed by chromato- graphic techniques and inorganic mercury concentrations are calculated from the difference between the results of the chromatographic analysis and the total mercury value of the sample. In all cases extraction of the methylmercury moiety to an organicsolventis necessary prior to any chromatographic Separation and detection. The alternative method is to derivatize methylmercury and inorganicmercury to molecular fully alkylated species and chromatograph the nonpolar derivatives in an appropriate gas chromatographic column. Such a method was described recently using NaB(C2H6)4 as an aqueous phase derivatizing reagent for organolead and organomercury compounds.16 It has also been used for the speciation of mercury, using a two-stage purge and trap chromatography with atomic fluorescence detection” and conventional gas chromatography coupled with atomic ab- sorption detection.18 In the present paper, we report the speciation of CH3Hg+ and Hg2+ using a simple purge-and- trap gas chromatography atomic absorption system. For fish samples a simple dissolution step in alkaline methanolic solution is followed by in situ derivatizationusing N ~B(CZH~)~ in the reaction flask of the apparatus. The derivatives CH3- HgC2H5 and (CzHd2Hg are purged on-line and trapped in a packed chromatographic column cooled by liquid nitrogen. (9) Berman, S. S.; Siu, K. W. M.; Maxwell, P. S.; Beauchemin, D.; Clancy, V. P. Fresenius’ 2. Anal. Chem. 1989,333, 641-644. (10) Jiang, G.; Ni, Z.; Wang, S.; Han, H. Fresenius’ 2. Anal. Chem. (11) Bulska, E.; Baxter, D. C.; Frech, W. Anal. Chim. Acta 1991,249, (12) Horvat, M. Water, Air Soil Polht. 1991, 56, 96-102. (13) Takunori, K.; Takashi, U.; Akio, Y.: Masatoshi. M. J. Anal. At. 1989,334, 27-30. 545-554. Spectrom. 1992, 7, 15-18. (14) Moreton, P. Ph.D. Thesis, Leicester Polvtechnic. U.K.. 1984. (15) Rapsomanikis, S. In Environmental Ahalysis Using Chroma- tography Interfaced with Atomic Spectroscopy; Harrison, R. M., Rapsomanikis, S., Eds.; Horwood: Chichester U.K., 1989; Chapter 10. (16) Rapsomanikis, S.; Donard, 0. F. X.; Weber, J. H. Anal. Chem. 1986,58, 35-37. (17) Bloom, N. Can. zyxwvu J. Fish. Aquat. Sci. 1989,46, 1131-1140. (18) Rapsomanikis, S.; Craig, P. J. Anal. Chim. Acta 1991,248, 563- 567. 0 1993 Amerlcan Chemical Society