Research On The Liqmid Cathode Glow Discharge Based SpectrΜm Detecting System And Its Applications

With the development of the industry, water is seriously polluted, and is harmful to safety of life. For thesafety of life, it is an urgent action to detect materials in the solution and further to understand their composition and content. The liquid electrode discharge, based on the principle of the gas discharge, is a new kind of plasma technology through which the plasma is generated by using the liquid as an electrode. This technology, with the merits of compact structure, simple operation, stable performance and being able to work under the atmospheric pressure, has a wide application prospect. Based on the technique of electrolyte cathode atmospheric pressure glow discharge atomic emission spectroscopy（ELCAD-AES）, the present study established a liquid cathode glow discharge spectrum detection system, and the system optimization, the discharge characteristics and performances, the applications in life were also launched. It will provide a technical support to the development of product miniaturization of the ELCAD-AES.Firstly, in order to improve the discharge performance, the component units of this system were reasonably optimized, including the sink fountains cold cutting typed liquid cathode, the peristalsis circulating typed fluid structure, and the three-dimensional adjustable platform. The experimental results reveal that the present system is a glow discharge system with linear volt-ampere characteristics（linearity higher than 99.4%）. In addition, excitation temperature of the discharge plasma, varied from 3562.93 K to 5247.81 K, is very low, which is proportional to the current intensity. However, the electron number density, varied from 1.804898× 10¹⁵cm^-3 to 1.955778 × 10¹⁵cm^-3, is inversely proportional to the current intensity.Then, several parameters, such as the electrolyte property, the discharge current intensity, the discharge spacing and the infusion velocity, which impact the optimum discharge condition, were studied. Through comparison and spectral analysis, it is found that the HNO₃ is more suitable than the HCl and H₂SO₄ to adjust the PH value of the electrolyte. Under the condition of stable discharge, the appropriate discharge space, PH value, current intensity and fluid flow varied from 1 mm to 2 mm, 1 to 2, 30 m A to 43 m A, and 2.5m L/min to 4m L/min, respectively.Once again, by emplaying the method of internal standard method, quantitatively analysis was carried out with various metal elements, such as Cd, Ni, Fe, Mn, Mg, Cu, Al, Ca and Zn. It is found that there is a good linear relationship between the concentration of the nine elements and the spectral intensity, with a linearity higher than 99% and an error range from-5% to +8%. The experimental results show that the detection limit has a magnitude of ppm（mg/L）, which is at the leading edge of this field. Furthermore, it reveal s that the detection system has good stability, high accuracy and a low error.At last, in order to evaluate the application of the present system, the hardness of three kinds of water and the elemental composition of milk powder were detected. It shows that the hardness of the city water, pond water and ground water are very different before and after boiling because of the existence of temporary hardness. On the other hand, compared with the commercial milk powder products, the detecting content of Ca, Mg, Fe, Zn element exhibits an error range from-10.0% to +9.72%. It reveals that the present detection system has the possibility of application in life, but the detection precision should be further improved.The present findings of this thesis provide a valuable support for the further research on liquid cathode glow discharge emission spectrum system.