Centrifugation Assisted Two-Phase Hollow-Fiber Liquid-Phase Microextraction Coupled With Direct Fluorimetry for Precise Thiamine Detection

To address the poor reproducibility associated with manual acceptor phase collection in two-phase hollow-fiber liquid-phase microextraction, we introduce a novel centrifugal collection technique for the first time. Thiamine, selected as a model analyte, was oxidized into fluorescent thiochrome and extracted via hollow-fiber liquid-phase microextraction. Following extraction, centrifugation at 7000 rpm quantitatively transferred 15.7 ± 0.4 µL (relative standard deviation [RSD] 2.55%) of the acceptor phase, accounting for over 80% recovery, from the hollow fiber into a glass capillary for direct fluorescence detection. This procedure enhanced collection efficiency nearly 7-fold and reduced RSD to 2.55%, compared with 2.3 ± 0.5 µL and 21.74% for the conventional syringe-based method. Optimal extraction conditions were established as follows: n -heptanol as the acceptor phase, a 20 min extraction time, 400 rpm orbital shaking, 15% NaCl, and 8 min for acceptor phase loading. Under these optimal conditions, a good linear relationship was established for thiamine across the concentration range of 0.05–3.0 µg/mL ( R 2 = 0.9996), with recoveries exceeding 91.0% and a limit of detection (LOD) of 1.112 × 10 −2 µg/mL. The intra-day and inter-day RSD ( n = 7) were below 1.7%. The proposed centrifugal collection method is simple, highly reproducible, and efficient, offering a generic strategy to enhance reliability and throughput for the hollow-fiber liquid-phase microextraction technique.