Determination of Iodine Species in Seafood by Ionic Liquid–Based In-line Solid-Phase Extraction-Capillary Electrophoresis

Ionic liquid (IL)–based in-line solid-phase extraction (SPE)-capillary electrophoresis (CE) method was developed for determination of three iodine species (3,5-diiodo-l-thyronine, l-tyrosine, 3,5-diiodo-l-tyrosine) in seafood. The background electrolyte (BGE) used was 5 mM sodium tetraborate. The small SPE extractor filled with Oasis HLB sorbent was constructed and embedded 7.5 cm away from the entrance to the capillary, then the ILs were used as eluting solvents to elute analytes and separate the target compounds to improve the detection sensitivity in CE. Several parameters including the elution solvent, the elution time, pH of sample solution, and sample loading time were investigated. The LODs were 0.48 ng/mL for 3,5-diiodo-l-thyronine, 4.7 ng/mL for l-tyrosine, and 5.2 ng/mL for 3,5-diiodo-l-tyrosine under optimal experimental conditions. Compared with normal hydrodynamic injection, sensitivity enrichment factors for this enrichment strategy ranged from 11 to 9635. The in-line SPE-CE method was then applied to analyze kelp and seaweed samples, and the recoveries ranged from 87 to 117%.