Usefulness of ionic liquids as mobile phase modifiers in HPLC-CV-AFS for mercury speciation analysis in food

Abstract

Different ionic liquids (ILs) were studied in this work as mobile phase modifiers for the separation and determination of Hg²⁺, methylmercury (CH₃Hg⁺) and ethylmercury (C₂H₅Hg⁺) species by reversed-phase high-performance liquid chromatography coupled to UV-cold vapor atomic fluorescence spectrometry (RP-HPLC-UV-CV-AFS). Several parameters influencing the chromatographic separation of Hg species, such as pH, sodium chloride concentration, organic solvent concentration, as well as chemical structure and concentration of ILs were evaluated. After a careful optimization, the separation of Hg species was achieved within 12 min using a C₁₈ column and a gradient developed by mixing methanol and a solution composed of 0.4% (v/v) 1-octyl-3-methylimidazolium chloride [C₈mim]Cl, 100 mmol L⁻¹ NaCl and 20 mmol L⁻¹ buffer citric acid/citrate at pH 2.0. In addition, a multivariate methodology was applied to optimize the parameters involved in UV-CV-AFS detection of Hg species. The proposed method allowed the separation of inorganic and organic Hg species in a single chromatographic run. The limits of detection obtained for Hg species were in the range of 0.05–0.11 μg L⁻¹. The usefulness of the proposed method was demonstrated by performing Hg speciation analysis in highly complex samples, such as seafood, yeast and garlic, obtaining accurate and precise results in all cases.