Design And Research Of Nitrite Monitoring System Based On Raman Spectroscopy

Nitrite is a highly toxic substance but is used as a food additive. Nitrite is very similar to salts because its excessive use or intake causes poisoning, and the consequences can be serious. However,following ingestion excessive amount of nitrite,the nitrite could transforms the normal haemoglobin into methaemoglobin, resulting in the loss of oxygen carrying capacity of haemoglobin and consequently in tissue hypoxia,the body could be harmful. Nitrite can also harm aquatic organisms and thus seriously affects the economic benefits of aquaculture. Therefore, the development of a rapid, real-time online nitrite detection system for food safety and aquaculture has an important significance.The hardware part of the system including the optical system and the electronic system. The optical system is based on resonance Raman technical design, and the combination of liquid core optical fiber technology can greatly enhance the Raman intensity. Design of the optical system includes five aspects, the selected optical source, preparation liquid-core optical fiber, filter selection,selection of spectral monochromator and a detector selection, then determine the module complies with the design requirements of this paper by test and analysis. After conditioning the optical path to achieve the conversion between an optical signal to an electrical signal. In addition, CCD driving pulse is generated and controlled by the STM32, between the CCD output and STM32 input has adding a signal conditioning circuit for signal tuning. The current is converted and amplification to an appropriate voltage, then filtering, so that the voltage amplitude within the allowable range for ADC in the STM32. STM32 communication with the host computer using RS232 serial communication. On the one hand, after the digital conversion value of the incoming PC for display,on the other hand into the SD card for backup.The software part of the system functions implemented including CCD driver, ADC driving,storage, communications, and LabVIEW graphical display. CCD driver allows STM32 chip provides certain duty cycle clock pulse signal, so that each CCD pixel signal charge generated in the final transfer out into an electrical signal corresponding to the light intensity. ADC driver acquisitionsignal from Raman scattered light intensity information which was treated by conditioning modules.Stored program stored detection system date and time information, facilitate inquiries and transaction history data. Communication program is to communicate with the host computer using a standard RS232 protocol. Design of spectrometer applications was based on LabVIEW, exhibits the spectrum collected from spectrometer, which can controlled the spectrometer parameters and storaged the spectral data.Experimental results show that the system could monitoring the concentration of nitrite ion in an aqueous solution. System successfully completed the collection, processing and display of the spectral data, can also be applied to detection nitrite in a variety of water samples, with good reproducibility, high accuracy.