A method proposed by Bouyssiere et al. [3] for mercury speciation in gas condensates by GC-ICP-MS was investigated for the determination of Hg2+ (as inorganic mercury) and MeHg+ in crude oil samples. The Grignard reaction conditions and instrumental parameters were optimized. The original volume (0.5 mL) of the Grignard reagent was duplicated, and a sample/toluene ratio of 1: 19 was used to avoid the total consumption and/or destruction of the Grignard reagent by the components of the oil matrices. Furthermore, the split injection mode was applied. When BuMgCl was used for the derivatization reaction, a limit of detection of 0.03 mu g L-1 Hg2+ was obtained. Precision was always better than 12%. Quantitative recoveries (80-117%) of Hg2+ (as MeBuHg and Bu2Hg) were obtained for the determination of MeHg+ and inorganic mercury in spiked samples, respectively. Besides BuMgCl, other Grignard reagents such as MeMgCl, EtMgCl and PrMgCl can be used for the determination of Hg2+ as inorganic mercury and MeHg+. Moreover, mercury species such as Me2Hg, MeEtHg, Et2Hg, Pr2Hg and MePrHg can be determined by direct injection into the CG-ICP-MS using Bu2Hg standard solutions for external calibration. (C) 2013 Elsevier Ltd. All rights reserved.