Abstract
The simulation of the gas flow field and electrostatic field in the photoionization detector by COMSOL was conducted based on principle investigation in the present study. Under the guidance of simulation results, structural optimization was carried out to significantly reduce the dead volume of the ionization chamber, and finally, the relationship between offset voltage and collection efficiency was obtained which led to a remarkable increase in the collection efficiency of charged ions in the photoionization detector. Then an ionization chamber with low interference and fast response was developed. Then experiment was performed with toluene as a VOCs gas under the condition of optimal gas flow rate of 50 ml, UV lamp ionization energy of 10.86 eV. The results showed that the ion collection efficiency reached 91% at a bias voltage of 150 V. Moreover, a preferred linearity of 99.99% was obtained, and a ppb level of LOD can be achieved. The determination results well-fitted the relationship between offset voltage and the response value obtained in the simulation.
Highlights
Volatile organic compounds (VOCs) is the general term of volatile organicity even at room temperature, which can influence our daily life and can threaten human being’s health [1]
We have developed a microfluidic PID that can be used in a GC system for rapid and highly sensitive VOCs detection
The photoionization current was defined as the quantity of an ion pair generated by ionization per unit time and can be showed as dNi = 2σiφ 1 − e−σiN t l, dt with Ni denoting the quantity of the ion pair, σi denoting the absorption coefficient of photoionization, φ denoting the quantity of photons injected into the ionization chamber per unit time, σ0 denoting the absorption coefficient caused by other reasons, σt = σi + σ0 was the total absorption coefficient, N t was the amount of gas molecule to be determined, namely, the gas concentration to be determined, and l denoting the optical path length
Summary
Volatile organic compounds (VOCs) is the general term of volatile organicity even at room temperature, which can influence our daily life and can threaten human being’s health [1]. The sensitivity of the photoionization detector is greatly influenced by the performance of the ionization chamber. 10−10 of the commercialized PID by HNU in 1976, companies such as RAE and Ion Science introduced the PID detection devices [6] These devices are complex in structure, lack scale production, are not competitive in the market, and cannot meet the requirements of trace detection. The photoionization detector is a versatile, selective detector that responds to most organic compounds and acts as a nondestructive detector. The sensitivity of the photoionization detector was mainly determined by ionization chamber performance [9], and the detection level of PID was generally determined by the quantity of electron flow produced in the ionization chamber. The photoionization detector has been integrated into the GC (μGC) system [10]
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