槲皮素为天然黄酮类化合物, 广泛存在于植物的根、 茎、 叶、 花和果实中。 槲皮素作为荧光探针检测氟离子不仅具有较好的选择性和灵敏度, 而且与合成的荧光探针比, 还具有来源广、 环保、 无毒等优点。 实验将不同阴离子（F－, Cl－, Br－, I－, ClO－4, H2PO－4）分别加入到槲皮素的二甲基亚砜（DMSO）溶液中, 考查槲皮素溶液的荧光强度变化。 实验发现当加入氟离子后, 槲皮素在500 nm处的荧光发射峰的强度降低, 发生荧光猝灭, 且其猝灭程度随着氟离子浓度的增大而改变, 即荧光强度随着氟离子浓度的增大而减小, 并呈线性变化。 而其他阴离子的加入对槲皮素和槲皮素-氟离子体系的荧光发射强度影响不大, 说明其他阴离子不影响槲皮素对氟离子的识别, 显示了槲皮素对氟离子具有较好的选择性。 由荧光滴定光谱和荧光滴定曲线得到槲皮素对氟离子的滴定方程为: y=－13.36x+173.4, 线性关系为R2=0.991, 线性范围为1.0×10－6～8.0×10－6 mol·L-1, 最低检测限为1.0×10－7 mol·L-1, 表明槲皮素对氟离子的识别具有较高的灵敏度。 进一步实验表明槲皮素识别氟离子的机理可能是氟离子的加入破坏了溶液体系的氢键, 改变了槲皮素分子的共轭状态, 发生分子内电荷转移, 促使槲皮素荧光猝灭。 用该法成功检测了样品中微量氟离子, 回收率为100.67%～102.44%, 精确度较好, 测定结果稳定。

Quercetin (Q) is one of the most common flavonoids present in roots, stems, leaves, flowers and fruits of most plants. In this study, a quercetin-based fluorescent probe for detecting fluorid ions had been proposed. With good selectivity and sensitivity for fluorid ions, Q-based fluorescent probe was easier to prepare, more eco-friendly and more innoxious compared with traditional fluorescent probe obtained by organic chemistry synthesis operation. There was a major fluorescence emission peak at 500 nm for Q in dimethyl sulfoxide (DMSO) when the excitation wavelength was 390 nm. The changes of fluorescence spectra were investigated before and after adding different anions into Q solution. The fluorescence emission intensity of Q even had no change when adding Cl－, Br－, I－, ClO－4, H2PO－4, respectively. While adding fluorid ions, the fluorescence emission intensity of Q was decreased obviously, which suggested fluorid ions could induce fluorescence quenching of Q in DMSO. And the fluorescence emission intensity of Q-F－ system had almost no significant change when adding other anions (Cl－, Br－, I－, ClO－4, H2PO－4), which meant the progress for detecting fluorid ions didn’t be affected by other anions, and Q showed a good selectivity for fluorid ions. The fluorescence titration spectra showed that the fluorescence emission intensity of Q was decreased with the increase of concentration of fluorid ions, and they were in concentration-dependent manner. The fluorescence titration curve exhibited that the Q as fluorescent probe can be applied to the quantification of fluorid ions with a good linearity (R2=0.991), linear range of 1.0～8.0×10-6 mol·L-1 and the detection limit of 1.0×10－7 mol·L-1. Not only the changes appeared in fluorescence spectra, but also the changes appeared in UV-visible spectra, compared with Q absorption spectrum, the location of band at 375 nm had no change after adding Cl－, Br－, I－, ClO－4, H2PO－4, respectively. However, when adding fluorid ions, the band at 375 nm was shifted to 394 nm, and the color of the solution was changed into dark yellow, which revealed the interactions between Q and fluorid ions. The probable mechanism of fluorid ions inducing fluorescence quenching of Q was obtained with 1H NMR spectrum and the changes of fluorescence emission intensity of Q-F- system in different polar solvents (DMSO containing different concentration of water). The interaction mode about Q and fluorid ions in DMSO was related with hydrogen bond. Both experiments suggested that the possible recognition mechanism on fluorid ions was: fluorid ions were destroyed or weakened by original hydrogen bonds, and were promoted charge transfer within quercetin molecule, which resulted in fluorescence intensity decreasing of quercetin. This method was successfully applied in detecting fluorid ions of samples in DMSO with good recovery.