To decrease signal fluctuations of glow discharge, several knots were tied in rubber tubing of peristaltic-pump. The discharge system mainly consists of two parts:
a pointed platinum anode with a diameter of 1 mm was sealed into a quartz tube, while the water samples were pumped through the quartz capillary and flowed over the top of the capillary which in turn was served as the cathode. The quartz capillary was passed through a hole on the graphite rod. The excess part of capillary with graphite carbon rod was 2.5 mm. The graphite rod was fixed on the plug of reservoir. The discharge gap between the tip of the platinum and the top of the quartz capillary was about 2 mm. The solution, which overflowed from the tip of quartz capillary, was flowed into the reservoir by means of many grooves on the graphite rod. When the voltage was sufficiently high, the glow discharge plasma was produced between the electrolyte around quartz capillary cathode and needle-like Pt anode.