Deyi Kong

Humidity effects on resolution and sensitivity of UV-FAIMS in VOCs detection

Humidity is a key environmental parameter for VOCs detection technology. A study of the effects of humidity on both resolution and sensitivity of UV-FAIMS was performed at ambient temperature and pressure. This study was based on the detection and analysis of the differences in spectra (height, position and shape) and the α function of VOCs under different degrees of humidity. A total of three types of VOCs (ketones, alcohols and aromatics) were chosen as detection samples and a self-developed UV-FAIMS as a measurement instrument. The results show that sensitivity is inversely proportional to humidity for all VOCs. In addition, the resolution–humidity relationship exhibits strong dependence on the polarity of the sample ions. As relative humidity increased from 0% to 100%, the sensitivity of ketones, alcohols and aromatics was reduced by 30.9–73.0%, 40.3–64.3% and 75.1–91.6%, respectively. However, increasing humidity significantly enhanced the resolution of ketones and alcohols in the ranges of 1.82–11.82 times and 1.23–6.69 times, respectively, and hardly affected that of aromatics. Consequently, the appropriate humidity of carrier gas is of great importance in the use of UV-FAIMS.

Effects of the Discharge Parameters on the Efficiency and Stability of Ambient Metastable-Induced Desorption Ionization

Ionization efficiency is an important factor for ion sources in mass spectrometry and ion mobility spectrometry. Using helium as the discharge gas, acetone as the sample, and high-field asymmetric ion mobility spectrometry (FAIMS) as the ion detection method, this work investigates in detail the effects of discharge parameters on the efficiency of ambient metastable-induced desorption ionization (AMDI) at atmospheric pressure. The results indicate that the discharge power and gas flow rate are both significantly correlated with the ionization efficiency. Specifically, an increase in the applied discharge power leads to a rapid increase in the ionization efficiency, which gradually reaches equilibrium due to ion saturation. Moreover, when the discharge voltage is fixed at 2.1 kV, a maximum efficiency can be achieved at the flow rate of 9.0 m/s. This study provides a foundation for the design and application of AMDI for on-line detection with mass spectrometry and ion mobility spectrometry.

High sensitivity field asymmetric ion mobility spectrometer

A high sensitivity field asymmetric ion mobility spectrometer (FAIMS) was designed, fabricated, and tested. The main components of the system are a 10.6 eV UV photoionization source, an ion filter driven by a high voltage/high frequency n-MOS inverter circuit, and a low noise ion detector. The ion filter electronics are capable to generate square waveforms with peak-to-peak voltages up to 1000 V at frequencies up to 1 MHz with adjustable duty cycles. The ion detector current amplifier has a gain up to 1012 V/A with an effective equivalent input noise level down to about 1 fA/Hz1/2 during operation with the ion filter at the maximum voltage and frequency. The FAIMS system was characterized by detecting different standard chemical compounds. Additionally, we investigated the use of a synchronous modulation/demodulation technique to improve the signal-to-noise ratio in FAIMS measurements. In particular, we implemented the modulation of the compensation voltage with the synchronous demodulation of the ion current. The analysis of the measurements at low concentration levels led to an extrapolated limit of detection for acetone of 10 ppt with an averaging time of 1 s.

Identification of Toxic VOC Pollutants Using FAIMS

Toxic Volatile Organic Compound (VOC) pollutants have seriously affected public health. FAIMS is a quick and high sensitive gas-phase ion detection technique. In this paper, a FAIMS system has been built and various VOCs detections are performed to evaluate the suitability of the systems separation effect. Finally, the relation between the waveform and the compensation voltage is discussed. The comparative experiments provide a useful reference for the subsequent optimization of toxic VOC pollutants detection with FAIMS.

Detection of benzene series by two-dimensional FAIMS technique

Benzene, toluene, p-xylene, m-xylene and o-xylene are harmful to human body seriously, moreover, p-xylene, m-xylene and o-xylene are isomers, which are difficult to distinguish by commonly used spectrum analysis techniques, such as mass spectrometry. In this article, they were detected by using high field asymmetric waveform ion mobility spectrometry (FAIMS). The resolution of detecting samples was optimized by two dimensional scanning concerning the compensation voltage in combination with high dispersion voltage. FAIMS has good solution to identify them. According to the experimental results, we obtained two-dimensional spectra. By fitting of equations about electric field intensity, we worked out second-order and fourth-order coefficient of ion mobility nonlinear function, which is useful to establish characteristic FAIMS spectra of the benzene series compounds.