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An atmospheric-pressure plasma sustained by an ac power supply was generated using electrolyte solution as one of the electrodes. By altering the power supply, ring-like patterns, double-ring patterns and plasma-spot patterns were observed at the electrolyte-electrode surface. Synchronous current-voltage characteristics and time-resolved images were measured. Important factors for the self-organized patterns, including the electrode gap, power, frequency and electrolyte concentration, were explored. The optical spectrum characteristics of the device were investigated. The pH of the solution after discharge was also explored and the results show that the pH of the solution is evidently reduced after the discharge, implying that acidic components are produced in the solution. This study provides an alternative discharge method for producing patterns on a water surface.

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Six types of tea leaves, including Longjing green tea, Mengding Huangya, white tea, Tie Guanyin, Wuyi black tea and Pu'er tea, were analyzed and identified using laser-induced breakdown spectroscopy (LIBS) combined with the discriminant analysis (DA) method.

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The trace mercury in aqueous solution is determined by laser-induced breakdown spectroscopy (LIBS) under the assistance of solution cathode glow discharge (SCGD) system. The aqueous solution is converted to gas phase using high voltage DC discharge, and then the generated mercury vapor is cooled by gas-liquid separator to improve the concentration of mercury. Finally, a 1064 nm wavelength Nd: YAG laser is used to produce plasma. In the present experiment, the characteristic spectral line of Hg I 253.65 nm is selected for analysis, under the optimal conditions of LIBS, the influences of the acid anion, discharge current, sample flow rate and carrier gas flow rate are investigated. The temporal behavior of the electron temperature and electron number density are also investigated, the results show that the electron temperature decreases from about 10900 K to 8800 K with delay time from 200 ns to 6 μs, and the electron number density is on the orders of 10 17 and 10 18 cm -3 , and it decreases with delay time. The analytical performances of this method are evaluated under optimized conditions, the calibration curve of Hg is plotted based on the different concentrations measurement results, and the detection limit (LOD) of Hg is calculated to be 0.36 mgL -1 . By using this experimental configuration, the detection limit and sensitivity of Hg are improved to some extent. This method provides an alternative analytical method for measurement of trace mercury in water.

Laser induced breakdown spectroscopy (LIBS) provides a useful technique for food security as well as determining nutrition contents. In this paper, optical emission studies of laser induced plasma on commercial tea samples were carried out. The spectral intensities of Mg, Mn, Ca, Al, C and CN vibration bands varying with laser energy and the detection delay time of an intensified charge coupled device were studied. In addition, the relative concentrations of six microelements, i.e., Mg, Mn, Ca, Al, Na and K, were analyzed semi-quantitatively as well as H, for four kinds of tea samples. Moreover, the plasma parameters were explored, including electron temperature and electron number density. The electron temperature and electron number density were around 11000 K and 10 17 cm −3 , respectively. The results show that it is reasonable to consider the LIBS technique as a new method for analyzing the compositions of tea leaf samples.