Determination of methylmercury and estimation of total mercury in seafood using high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS): Method development and validation

A method was developed for determination of methylmercury and estimation of total mercury in seafood. Mercury (Hg) compounds were extracted from 0.5 g edible seafood or 0.2 g lyophilized reference material by adding 50 ml aqueous 1 % W/V L-cysteine(.)HCl(.)H(2)O and heating 120 min at 60 degrees C in glass vials. Hg compounds in 50 mu l of filtered extract were separated by reversed-phase high performance liquid chromatography using a C-18 column and aqueous 0.1 % W/V L-cysteine(.)HCl(.)H2O + 0.1 % W/V L-Cysteine mobile phase at room temperature and were detected by inductively coupled plasma-mass spectrometry at mass-to-charge ratio 202. Total Hg was calculated as the mathematical sum of methyl and inorganic Hg determined in extracts. For seafoods containing 0.055-2.78 mg kg(-1) methylmercury and 0.014-0.137 mg kg-1 inorganic Hg, precision of analyses was <= 5% relative standard deviation (R.S.D.) for methylmercury and <= 9% R.S.D. for inorganic Hg. Recovery of added analyte was 94% for methylmercury and 98% for inorganic Hg. Methyl and total Hg results for reference materials agreed with certified values. Limits of quantitation were 0.007 mg kg(-1) methylmercury and 0.005 mg kg(-1) inorganic Hg in edible seafood and 0.617 mg kg(-1) methylmercury and 0.012 mg kg(-1) inorganic Hg in lyophilized reference materials. Evaluation of analyte stability demonstrated that L-cysteine both stabilized and de-alkylated methylmercury, depending on holding time and cysteine concentration. Polypropylene adversely affected methylmercury stability. Total Hg results determined by this method were equivalent to results determined independently by cold vapour-atomic absorption spectrometry. Methylmercury was the predominant form of Hg in finfish. Ratios of methylmercury/total Hg determined by this method were 93-98% for finfish and 38-48% for mollusks. (c) 2006 Elsevier Inc. All rights reserved.