Study On Detection Methods Of Endocrine Disruptors Triphenyltin With Raman And SERS

The deterioration of the human environment caused by environmental pollution has caused widespread concern in the community. However, some environmental contaminants, for example organotin compounds, with low content, high toxicity in the environment, are rarely able to directly detect, which can be detected after a a series of sample pretreatment such as separation, concentration and derivatization. It is often unconducive to the realization of rapid, non-destructive and real-time online detection of organotin residue. Raman scattering technology contains large amount of information,spectral specificity, without complicated sample pretreatment, which can be used to achieve rapid, nondestructive and real-time detection of organotin compounds. Raman spectroscopy shows great development potential in the field of the environment especially after the appearance of surface enhanced spectroscopy.This thesis choose triphenyltin(TPT) as the research object, use laser confocal Raman spectrometer as main equipment, with Raman spectroscopy and surface enhanced Raman spectroscopy(SERS) as detection methods, conducted a study on the environmental endocrine disruptors TPT. This study explored the optimal experimental conditions for detection of TPT with Raman spectroscopy, attributed and analyzed their assignments of the the collected TPT spectrum, established the standard Raman spectrum database of TPT. Then a wide range of pH values were carried out to choose the optimum pH value in TPT detection by Raman spectroscopy. Afterwards, Raman and SERS spectra of different various TPT solutions were collected and analyzed. At last, the study applied Raman scattering technique on the residue detection of TPT on apple skin, and finally determined the detection limit of Raman and SERS detection of TPT residues of apple skin. The results would be used to identify the presence of TPT residual in real environmental samples, which provide a theoretical basis and data base on Raman spectroscopy. The specific work contents and results of this study are as follows:1) This experiment collect the Raman signal of TPT standard powders by Laser confocal Raman spectroscopy to explore the feasibility of the method and explore the optimized parameters. In this paper, we combined the application of Laser confocal Raman spectroscopy with the TPT physical property. Due to different functional groups of TPT molecules shows different vibration modes, the Raman spectra was divided intothree wavenumber areas(1500~3200, 900~1500, and 100~900 cm-1) to attribute and analysis their assignments of the Raman peaks, obtain the characteristics of TPT vibration modes and the corresponding characteristic peaks. Finally, a standard Raman spectra library was established with the spectral range between 100~ 3200 cm-1. The results showed that the Raman spectra with high signal-to-noise ratio can be obtained in a short time when the excitation wavelength is 785 nm with the laser power options decayed to 0.5% of the original power(500mW) after 10 s exposure and 2 times integration. Strong Raman signals observed in the Raman spectroscopy at 212, 332, 657,997, and 1577 cm-1 could be used as the characteristic peaks of TPT in Raman detection.Otherwise, the co-occurrence of the Raman peaks at 657 and 997cm-1 can be considered as the presence of TPT in complex environmental samples.2) The study collected Raman spectra of several common laboratory base: load glass slide, glass capillary, aluminum foil, quartz plate, copper and aluminum tablets,and then choose the most suitable substrate for TPT solution detection by Raman spectroscopy. Then a wide range of pH values were carried out to choose the optimum pH value in TPT detection by Raman spectroscopy. Finally, the normal Raman spectra of TPT standard solution was collected and analyzed qualitatively and quantitatively.The experimental results show that the aluminum is the optimal substrate for Raman detection of TPT solution. And the optimum pH value of TPT detection by Raman spectroscopy is 5.5 where the collected peak information is comprehensive with high signal-to-noise ratio. The high standard curve was established at 998 cm-1, there is a good linear relationship in 0.6~60 mg Sn/L with the correlation coefficient is R2=0.9904,Indicating that the residual TPT solution can be quantitative determinate by Raman spectroscopy.3) With silver colloid as surface strengthening agent, the experiment collected SERS spectra of a gradient concentrations of TPT standard solutions within the range0.6 ng Sn/L~3 μg Sn/L, and analyzed the collected spectral. Then the SERS spectra at concentration of 0.3 μg Sn/L of TPT standard solution and normal Raman spectra at concentration for of 30 mg Sn/ L standard solution of TPT were compared and analyzed to explicate the adsorption mode of TPT on silver colloid surface adsorption and the mechanism of SERS. Finally, the Raman and SERS peaks at 998 cm-1 of TPT solution was used to estimate the enhancement factor. The results show that the TPT solution signals were enhanced by chemical adsorption on silver colloid. Some surface enhanced Raman characteristic peak(such as 420, 689 cm-1 as the SERS characteristic peak)compared had significant shifts compared with the normal Raman spectrum characteristic peak(in 331, 657 cm-1 characteristic peak) suggesting that in π orbitals of three benzene rings may be interacted with the silver surface at the contact points,resulting in the parallel from molecular skeleton to the direction of the metal surface is slanted. In a word, the SERS with Ag NPs as surface enhancement agent is an effective method with an enhancement by 5 orders of magnitude and stretched the detection limit to 0.6 ng Sn/L within less than 30 s.4) Finally, in this study, the residual of TPT on apple skin was studied by casting diffirent concentrations of TPT(6.25 ng/cm2~2.5 μg/cm2) on apple skin under the current optimized condition. The result shows that TPT could be detected from its SESR spectra with Ag NPs as enhancement at as low as 6.25 ng/cm2 in standard solutions. The results show that the SERS technique is feasible to detect the residue analysis of pesticides TPT on apple skin. This innovative and promising method can be a breakthrough technology for TPT detection.