Xiaoguang Gao

Analysis of antibiotics from liquid sample using electrospray ionization-ion mobility spectrometry.

The recent findings of antibiotic residues in aquatic environment at trace level have gained much concern for the detrimental effect on ecological and human health due to bacterial resistance. Here, the feasibility of using electrospray ionization ion mobility spectrometry (ESI-IMS) for analysis antibiotics in liquid sample is demonstrated. Reduced mobilities and collision cross sections of 18 antibiotics are experimentally measured and compared with theoretical values according to mass-mobility correlation. Gentamicin is used as an example to investigate the capability of ESI-IMS for multi-component analysis of antibiotics. Mixtures of antibiotics at different concentrations are analyzed. The estimated detection limit for amoxicillin is 0.7 mg L(-1) (70 pg) and the linear range of response maintains over two orders. This method will be a potential technique for the analysis of antibiotics in aquatic environment.

Malathion detection method using microhotplate-based preconcentrator and ion mobility spectrometer

A simple and rapid method using a microhotplate-based preconcentrator and an ion mobility spectrometer (IMS) is proposed for the detection of malathion in water. The preconcentrator is prepared by micro-electro-mechanical system (MEMS) process. Coated with Polydimethylsiloxane (PDMS), it has the advantages of solvent-less, low energy cost, self-heating and ease to combine with IMS. The operating conditions of the preconcentrator-IMS system, such as extraction time, extraction temperature, agitation speed and desorption temperature, were optimised. Using the preconcentrator, the sampling procedure can be simplified and the detection limit of the system can be decreased. A linear relationship between the IMS response and the concentration of the analyte solution was verified. The malathion detection limit based on 3 times the baseline noise is 0.43 µg L−1 and the total analysis time is less than 30 minutes.

Corona Discharge Ionization Source for a Planar High-Field Asymmetric Waveform Ion Mobility Spectrometer

A corona discharge (CD) ionization source was prepared for a planar high-field asymmetric waveform ion mobility spectrometer (FAIMS). The effects of discharge current and discharge distance on ionization efficiency were investigated; and the electric field dependence of the ion injection in the reaction region was studied. The results showed that the discharge current of CD source had good linearity with the intensity of reactant ion peak (RIP), and the RIP intensity increased to a stable level at the discharge distance of >5 mm. An injection electrode was introduced to improve the ionization efficiency. A square-wave voltage applied to the electrode was found to provide optimal performance of ion injection and utilization. The operating parameters of the CD-FAIMS were optimized to achieve trace level detection of dimethyl methylphosphonate (DMMP) sample. The detection limit for DMMP was 0.5 µg/m3.

Detection of Toluene, Methanol and Formaldehyde Using Corona Discharge Ion Mobility Spectrometry

Polluted air, indoors, and outdoors, that contains hazardous matters or contaminants creates a hazard to general health. Ion mobility spectrometry is a very promising method for the detection of air pollutants. In this work, the experimental parameters of corona discharge ion mobility spectrometer (CD-IMS), such as the discharge distance, the drift tube temperature and the drift gas flow rate, are discussed and determined in terms of stable ionization and better reactant ion peak quality. The optimal conditions of the CD-IMS are applied to the detection of toluene, methanol and formaldehyde with the detection limits of 7.8, 11.3, and 4.6 ppbv, respectively. This provides an alternative and sensitive method for detection of air pollutants.

Determination of Malathion Using Corona Discharge – Ion Mobility Spectrometry with Solid-Phase Microextraction

ABSTRACT A corona discharge (CD) ion mobility spectrometer combined with solid-phase microextraction was constructed. The detection limit and stability of the system for malathion detection were improved using a novel sample introduction port through which the sample desorption was performed in high-temperature drift tube and the sample was introduced directly to the ionization area. The working parameters of the distance between CD needle tip and carrier gas outlet, the drift tube and carrier gas temperature, the carrier gas flow, and the voltage on CD needle were selected. When the extraction time for standard malathion was set to 5 min, the detection limit was 0.96 µg L−1 based on thrice the baseline noise, the linear range was 50–500 µg L−1, the correlation coefficient was approximately 0.9941, and the relative standard deviation was below 10%. Malathion-spiked lake water samples were analyzed using the developed system and the recovery was 92–102%. This method is suitable for the rapid detection of organophosphorus pesticide residues.

R-T relation of SnO/sub 2/-Ag thin film in temperature pulsed operation mode

The SnO/sub 2/-Ag thin film was prepared by magnetron sputtering on the Si-based membrane substrate embedded with a platinum micro heater. The sensitive properties of the film to H/sub 2/S were investigated, and the R-T relation was measured in temperature pulsed operation mode and in simple temperature ramp mode in order to understand the sensitive properties. The results are used to discuss the effect of Ag additive on the R-T relation and sensitive properties of the film. The variation of film resistance shows that the silver promotes the chemical processes on the surface of films. The R-T relation measured in temperature pulsed operation mode can be used to understand the sensing properties of SnO/sub 2/-Ag film.

Sensing characteristics of WO3 thin film as NO2 gas sensor

The WO3 thin films were prepared by magnetron sputtering method on the 3mm by 3mm silicon substrates with Pt interdigitating electrodes and heater. The deposition and the operating temperatures were analyzed to optimize the technological parameters. The sensing properties of these films to NO2 gas were measured. The result indicate that the sensitivities are strongly dependent on the deposition and operating temperatures. The WO3 thin film deposited at 300 degrees C and then annealed in air at 600 degrees C for 4h shows the excellent sensing properties to NO2 gas at the operating temperature of 250 degrees C.