Determination of chlorophenoxy acid herbicides by using a zirconium-based metal-organic framework as special sorbent for dispersive micro-solid-phase extraction and high-performance liquid chromatography

The present study reports on a Zr-based metal-organic framework (MOF) with 2-amino-benzenedicarboxylic acid (UiO-66-NH2) ligand as a special and efficient adsorbent for pretreatment of chlorophenoxy acid herbicides (CPAHs) from biosamples. Owing to the ionic bond formation between the amino groups of the MOF and the carboxyl groups of CPAHs, CPAHs could be selectively and easily adsorbed by the MOF material. On the other hand, by regulation of the pH value of the eluting solvent, CPAHs could also be easily eluted from the MOF. In addition, by characterization with the techniques of scanning electron microscopy, powder X-ray diffraction, and Brunner-Emmett-Teller surface area analysis, the as-synthesized material showed good characteristics of morphology, high specific surface area and large pore volume. Its performance was evaluated by the dispersive micro-solid-phase extraction (D-m-SPE) of CPAHs from vegetable samples, followed by high-performance liquid chromatography (HPLC) analysis. The parameters affecting the extraction efficiency were investigated and properly optimized. By combining the optimized D-m-SPE conditions with HPLC, a sensitive method for the determination of CPAHs was developed. In the linearity range of 10-1000 pmol mL(-1), the correlation coefficients were satisfactory (R-2 > 0.9985) for all the analytes; the LODs were 0.16-0.37 ng g(-1) based on a signal-to-noise ratio of 3; the intra-day and inter-day precision values (based on the relative standard deviation, n = 3) were under 3.1% and 5.9%, respectively; and satisfactory recoveries for all analytes in all samples were in the range of 82.3-102%. The results demonstrate that the synthesized Zr-MOF has a potential application of adsorbing CPAHs from complex matrix.