เอกสารประชุมวิชาการระดับขาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 2561

928 การประชุมวิชาการระดับชาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 ประจ�าปี 2561 Figure 5 Schematic illustration of the fluorescence quenching mechanism of TGA-capped CdTe QDs Analytical performances Under the optimal conditions, fluorescence spectra of the TGA-capped CdTe QDs with various concentrations of Pb 2+ were recorded (Figure 6A). The fluorescence intensity decreased as the concentration of Pb 2+ increased. Linearity between the F 0 /F and the concentration of Pb 2+ was obtained over the range of 0.05-50 mg L -1 with a coefficient of determination of 0.998 (Figure 6B). The linear regression was (0.0342x ± 0.0079)  (1.1366 ±0.017). The detection limit was 0.05 mg L -1 , which was calculated following the IUPAC criteria (LOD = 3 ʍ /k) where ʍ is the standard deviation of the blank measurements (n = 11) and k is the slope of the calibration curve. The proposed method exhibited good precision with a relative standard deviation of < 3.0%. Figure 6 Fluorescence spectra of TGA-capped CdTe QDs after addition of Pb 2+ various concentrations: a ,0.0; b, 0.05; c, 1.0; d, 3.0; e, 10.0; f, 30.0; g, 50.0; h, 100.0 (mg L -1 ) (A) and calibration curve of F 0 /F versus the concentration of Pb 2+ (B) Selectivity of the TGA-capped CdTe QDs for the determination of Pb 2+ The selectivity of the TGA-capped CdTe QDs for the analysis of Pb 2+ was investigated. As shown in Figure 7, the fluorescence intensities of the TGA-capped CdTe QDs were quenched by Pb 2+ and were insensitive to the other target cations Na + , Mg 2+ , K + , Zn 2+ , Ni 2+ and Fe 2+ . This result indicated the good selectivity of the TGA-capped CdTe QDs as a fluorescence probe for the determination of Pb 2+ .