In situ immobilization of layered double hydroxides onto cotton fiber for solid phase extraction of fluoroquinolone drugs.

Cotton fiber was proposed as a biodegradable support material. The properties like high specific area, hygroscopicity and adjustable shape make it be an idea substrate for solid phase extraction (SPE). In this work, inorganic layered double hydroxides (LDHs) were in situ immobilized onto cotton fiber through the linker of polydopamine as stationary phase. Uniform NiAl-LDHs crystal with nanostructure was observed on cotton fiber after one-step synthesis through urea hydrolytic method. The cotton fiber can not only increase the specific area and mass transfer rate, but also prevent aggregation and blocking of the freestanding LDHs crystal. Due to the electrostatic interaction and anion exchange features of LDHs, the prepared LDHs modified cotton fiber showed good extraction efficiency and selectivity towards fluoroquinolone drugs including norfloxacin, ciprofloxacin and enrofloxacin. After elution by 1 M NaOH, a simple acid-base neutralization method was proposed, so the natural elution can be directly analyzed by HPLC system. After optimizing the extraction parameters including adsorbent amount, sampling rate, sample volume, sample pH and eluent types and concentration, excellent extraction efficiency towards three fluoroquinolone drugs was obtained with high enrichment factors of 37-47. The adsorption capacity of LDHs modified cotton fiber was 21.18, 21.85 and 20.54 mg g-1 for norfloxacin, ciprofloxacin and enrofloxacin, which was almost twice as much as that of freestanding LDHs. The established method based on SPE-HPLC-FLC (fluorescence detector) technique exhibited good linearity (R2 ≥ 0.995), low limits of detection (0.01 µg L-1) and good reproducibility (intra-day RSDs ≤ 3.89%). Moreover, this method has also been applied in analyzing fluoroquinolone drugs in chicken eggs and pork liver.