Chen Chilai

Direct and Rapid Determination of Ammonia in Water Samples Using Ultraviolet Photoionization High Field-Asymmetric Waveform Ion Mobility Spectrometry

A novel on-site rapid detection method for ammonia detection in water was developed by using ultraviolet photoionization high field-asymmetric waveform ion mobility spectrometry (UV-FAIMS). The position of ammonia characteristic ion peak was acquired by the comparison between the characteristic compensation voltage (CV) in standard ammonia sample and trace amount ammonia in water. The relation between the positions of ammonia characteristic ion peaks under different dispersion voltages (DV) was studied. The values of alpha(2) , alpha(4) were 2.21 x 10(-5) Td(-2) and -1.45323 x 10(-9) Td(-4), respectively. The different concentrations of ammonia in water was measured with a limit of detection (LOD) of 9.2 mu g/L (S/N=3). This study provided a rapid, non-pretreatment means for the detection of ammonia in water matrices.

Simulation of Electrical Discharge Initiated by a Nanometer-Sized Probe in Atmospheric Conditions

In this paper, a two-dimensional nanometer scale tip-plate discharge model has been employed to study nanoscale electrical discharge in atmospheric conditions. The field strength distributions in a nanometer scale tip-to-plate electrode arrangement were calculated using the finite element analysis (FEA) method, and the influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of effective discharge range (EDR) on the plate were also investigated and discussed. The simulation results show that the probe with a wide tip will cause a larger effective discharge range on the plate; the field strength in the gap is notably higher than that induced by the sharp tip probe; the effective discharge range will increase linearly with the rise of excitation voltage, and decrease nonlinearly with the rise of gap length. In addition, probe dimension, especially the width/height ratio, affects the effective discharge range in different manners. With the width/height ratio rising from 1:1 to 1:10, the effective discharge range will maintain stable when the excitation voltage is around 50 V. This will increase when the excitation voltage gets higher and decrease as the excitation voltage gets lower. Furthermore, when the gap length is 5 nm and the excitation voltage is below 20 V, the diameter of EDR in our simulation is about 150 nm, which is consistent with the experiment results reported by other research groups. Our work provides a preliminary understanding of nanometer scale discharges and establishes a predictive structure-behavior relationship.