Methylmercury artifact formation during solid-phase extraction of water samples using sulfhydryl cotton fiber adsorbent

Preconcentration of methylmercury from dilute water samples by solid-phase extraction on a column packed with sulfhydryl cotton causes methylation of inorganic mercury. The effect is most severe for low concentrations of mercury in deionized water and environmental water samples, such as melted snow or rainwater, with low dissolved organic carbon (DOC) contents, resulting in up to 40% conversion of inorganic mercury to methylmercury. Although, in previous studies artifact methylmercury was attributed to the presence of naturally occurring DOC in the water, we find evidence for methylation especially in the absence of DOC. Indeed, high DOC content appears to suppress artifact formation. In such cases, binding of inorganic mercury by organic matter protects the mercury from methylation under the analysis conditions.