This work presents a new online method using gas chromatography coupled to the multicollector-inductively coupled plasma-mass spectrometer for methylmercury (MMHg) isotope ratio measurement. An extraction method using distillation was developed that effectively extracted MMHg from up to 5 grams of sediment, imparting no isotope fractionation on MMHg during extraction. Isotope ratios from transient signals were calculated using three different data treatment approaches, facilitated by a data processing application, IsoCor. Peak Area Integration using 80% of the peak gave the most accurate and precise results. Using the proposed methodology, an external precision (2 SD) of ± 0.59‰ for NIST 3177 was measured. This method can be applied to samples with MMHg concentration as low as 0.1 ng/g and was successfully applied to real sediment samples however, additional research to improve the precision of the method is required for the detection of small differences between samples.
Author Keywords: compound specific isotopic ratios, isotope ratio measurement, MC-ICP-MS, methylmercury