碲化镉量子点荧光开关法测定痕量铅

Determination of trace lead by cadmium telluride quantum dot fluorescence switch method

采用巯基丙酸(MPA)做稳定剂,在碱性介质中合成水溶性好、半峰宽窄、颗粒分散均匀的碲化镉(CdTe)量子点。在双硫腙存在的情况下,根据CdTe量子点荧光强度的恢复程度与铅离子浓度成正比的现象,建立了基于CdTe量子点荧光开关测定铅离子的新方法。在比色管中加入1mL 2.5×10-4 mol/L CdTe量子点溶液(浓度以Cd^(2+)计)、适量pH 10.0的硼砂缓冲溶液、1mL 90μmol/L的双硫腙乙醇溶液,充分反应5min后,加入不同浓度梯度的Pb^(2+)标准溶液,用pH 10.0的硼砂缓冲溶液定容至5mL后放置5min,于激发波长/荧光发射波长(λex/λem)为400nm/600nm测定体系的相对荧光强度。结果发现,铅离子浓度在2.0×10-6~9.0×10-5 mol/L范围内与其对应的相对荧光强度具有良好的线性关系,相关系数r=0.997 6,方法检出限为3.3×10^(-7) mol/L。采用实验方法对土壤和湖水样品中的铅进行测定,结果与原子吸收光谱法(AAS)基本一致,相对标准偏差(RSD,n=6)为0.99%~1.0%,回收率为95%~105%。

The cadmium telluride （CdTe） quantum dot with good water solubility, narrow peak width at half height and uniform particle dispersion was synthesized in alkaline medium using mercaptopropionic acid （MPA） as stabilizing agent. In presence of dithizone, the recovering extent of CdTe quantum dot fluorescence intensity was in direct proportion to the concentration of lead ions. Based on this phenomenon, a new determination method of lead ion by CdTe quantum dot fluorescence switch was established. To colorimetric tube were added into 1 mL of 2 .5×10^-4 mol/L CdTe quantum dot solution （in Cd^2＋ ） , proper amount of borate buffer solution at pH 10. 0 and 1 mL of 90 μmol/L dithizone ethanol solution. After complete reaction for 5 min, the Pb^2＋ standard solution with different concentration gradients was added. After diluting the solution to 5 mL with borate buffer solution at pH 10. 0 and placing for 5 min, the relative fluorescence intensity of testing system was measured at 400 nm/600 nm for excitation wavelength/ fluo-rescence emission wavelength （λex/λem）. It was found that the concentration of lead ion in range of 2 . 0×10^-6- 9.0×10^-5 mol/L showed good linearity to the corresponding relative fluorescence intensity. The correlation coefficient was r=0. 997 6, and the detection limit of method was 3. 3×10^-7 mol/L. The pro-posed method was applied to the determination of lead in soil and lake water samples, and the found results were consistent with those obtained by atomic absorption spectrometry （AAS）. The relative standard deviations （RSD, n = 6） were between 0. 99 % and 1.0%, and the recoveries were between 95% and 105 %.