Reseaech Of Trace Mercury Detection Method And Technology Basied On AAS

Heavy metal detection is an important basis and means for environmental monitoring and food safety control.According to environmental protection and food safety requirements,the detection limit of heavy metals is extremely low and must reach the ppt level.As a widely used trace mercury detection technology,atomic absorption spectroscopy has the advantages of high sensitivity and simple operation.However,existing detection instruments have problems such as low precision and high detection limit.This thesis started from the analysis of the factors affecting the detection limit,and carried out research on light source driving,light intensity stability control,optical path design as well as signal processing.We developed a trace mercury detection method based on atomic absorption spectroscopy,which effectively improves the system detection limit.The out-of-limit performance enables sub-pg-level trace mercury detection.The main research contents of the thesis are as follows:A trace mercury detection scheme based on atomic absorption spectroscopy was designed.Based on the trace mercury detection requirements,the common trace mercury detection method was analyzed and compared.The trace mercury detection structure based on atomic absorption spectroscopy was introduced.An overall implementation plan was proposed and the key technologies for improving system detection limits were pointed out.A driving and light intensity stabilization method of low-pressure mercury lamp was proposed.The equivalent model of the current-fed push-pull resonant circuit with low-voltage power supply was constructed.The circuit parameters were designed in combination with the starting voltage and current requirements of the low-pressure mercury lamp.The light was used as a feedback signal to construct a closed-loop system.The frequency domain analysis of system was analysied and optimization design was proposed to improve the reliability of the closed-loop control,which greatly improved the light intensity stability of the light source.The light intensity signal processing scheme based on the common point optical path structure and circuit noise optimization was proposed.The influence of the optical path structure on the light intensity feedback control effect was analyzed.A compact type was designed based on the light intensity stability data under different optical path structures.A common point optical path structure was designed,and beams of different angles at the same position of the lamp tube were selected as the detection beam and the feedback beam respectively.And the noise optimization design of the light intensity signal processing circuit was performed,thereby effectively improving the system noise and stability performance.The trace mercury detection system based on atomic absorption spectroscopy was built.The system noise and stability test experiments were carried out.The results show that the signal-to-noise ratio of the system is better than 40 d B,and the baseline drift in 30 minutes was less than 0.1‰.The system rating test and the detection limit verification test were carried out.The result showed that the system detection limit was 0.77 pg.The mercury content in rice,cosmetics and drinking water was quantitatively analyzed,and the detection error was less than 1pg.