Efficient and Selective Enrichment of Ultratrace Cytokinins in Plant Samples by Magnetic Perhydroxy-Cucurbit[8]uril Microspheres

Cytokinins play a critical role in controlling plant growth and development, but it is difficult to be determined in plant samples due to the extremely low concentration level of picomole/gram. So it is important for efficient sample preparation with selective enrichment and rapid separation for accurate analysis of cytokinins. Herein, a supramolecular perhydroxycucurbit[8]uril (PCB[8]) was fabricated into the Fe3O4 magnetic particles via chemical bonding assembly and magnetic perhydroxy-cucurbit[8]uril (MPC) materials were obtained. The MPC had good enrichment capability to cytokinins and the enrichment factors were more than 208. The interaction of MPC and cytokinins was investigated by adsorption test and density functional theory (DFT) calculation, the results showed that the main drive forces were the host guest interaction and hydrogen-bonding interaction between the perhydroxy-cucurbit[8]uril with analytes. Combined with ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), the MPC was used as a sorbent of magnetic solid-phase extraction for the analysis of cytokinins in plant samples. A sensitive and selective UPLC-MS/MS method was developed with low detection limits of 0.14-0.32 ng/L for cytokinins analysis. Five cytokinins including zeatin riboside, meta-topolin, kinetin, kinetin riboside, and zip with 6.12-87.3 ng/kg were determined in the soybean sprout and Arabidopsis thaliana. The recoveries were in the range of 76.2-110% with relative standard deviations (n = 5) of 2.3-9.7%. On the basis of these results, magnetic perhydroxy-cucurbit[8]uril material's with selective enrichment capability have good potential on the analysis of ultratrace targets from complicated sample matrixes.