Determination of Mercury in Food and Water Samples by Displacement-Dispersive Liquid-Liquid Microextraction Coupled with Graphite Furnace Atomic Absorption Spectrometry

A novel method was developed for the determination of mercury by displacement-dispersive liquid-liquid microextraction (D-DLLME) combined with graphite furnace atomic absorption spectrometry. The D-DLLME method is based on two steps of dispersive liquid-liquid microextraction (DLLME). First, Cu²⁺reacted with pyrrolidinedithiocarbamate (PDC) to form Cu-PDC complex and extract with DLLME procedure; then, the sediment phase was dispersed into the sample solution containing Hg²⁺with dispersive solvent, and another DLLME procedure was carried out. Since the stability of Hg-PDC is higher than that of Cu-PDC, Hg²⁺can displace Cu²⁺from the preextracted Cu-PDC complex and enter into the sediment phase. As a result, Hg²⁺was preconcentrated, and the interference from coexisting metal ions with lower PDC complex stability was largely eliminated as they cannot displace Cu²⁺from Cu-PDC complex. Under the optimal conditions, the limit of detection was 19 ng L⁻¹(3σ) for mercury, and an enhancement factor of 62 was achieved with a sample volume of 5.0 mL. The accuracy of the developed method was evaluated by analysis of the certified reference material GBW08508 rice flour. The method was successfully applied to determine the trace mercury in food and water samples with satisfactory results.