Ionic liquids as mobile phase modifiers for the separation of arsenic species in wine by liquid chromatography coupled to atomic fluorescence detection

CASTRO GRIJALBA, ALEXANDER; FIORENTINI, EMILIANO; WUILLOUD, RODOLFO G.

Santos

Congreso; 5th IBEROAMERICAN MEETING ON IONIC LIQUIDS (IMIL 2017); 2017

Universidade Estadual Paulista (UNESP)

The application of ionic liquids (ILs) as mobile modifiers for chromatographic separation of arsenite [As(III)], arsenate [As(V)], dimethylarsonic acid (DMA) and monomethylarsonic acid (MMA) species by reversed-phase high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry detection (RP-HPLC-HG-AFS) was studied in this work. Several factors influencing the chromatographic separation of the As species, such as pH of the mobile phase, buffer solution concentration, buffer type, IL concentration and length of alkyl groups in ILs were evaluated. Different ILs including, 1-butyl-, 1-hexyl-, 1-octyl-, 1-dodecyl- and 1-hexadecyl-3-methylimidazolium chloride were assayed. Also, tributyl(methyl)phosphonium methylsulphate was evaluated. The effect of ILs on HG-AFS sensitivity was studied. The complete separation of As species was achieved using a C18 column in isocratic mode with a mobile phase composed of 0.5% (v/v) [C8mim]Cl and 5% (v/v) methanol at pH 8.5. A multivariate methodology was used to optimize the variables involved in AFS detection of As species after HPLC separation. The ILs showed remarkable performance for the separation of As species, which was obtained within 18 min with a resolution higher than 0.83. The limits of detection for As(III), As(V), MMA and DMA were 0.81, 0.89, 0.62 and 1.00 µg As L-1. The proposed method was applied for As speciation analysis in white and red wine samples made from different grape varieties. The separation mechanisms involved when ILs are used in RP-HPLC could be attributed to different processes, i.e. anion exchange between As species and ILs retained on the stationary phase, but also possible interaction of ion pairs formed between ILs and As species with the C18 stationary phase. Moreover, the choice of an appropriate type and concentration of IL was critical to obtain complete separation. Thus, resolution of As species was observed to be strongly dependant on the alkyl chain length of imidazolium-type ILs.