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Development of a Novel Micro Photoionization Detector for Rapid Volatile Organic Compounds Measuremen 时间:2018-09-16 22:12 来源:未知作者:admin 点击: 次 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.
1. Introduction
Volatile organic compounds (VOCs) is the general term of volatile organicity even at room temperature, which not only can influence our daily life but also can threaten human being’s health [1]. By comparing the performance of different detectors, finding the appropriate VOCs detector, and comparing the working principle and performance characteristics of different detectors, the characteristics of different detectors are introduced in Table 1.
By comparing the performance of different detectors, it can be concluded that different types of detectors have different types of gases. The difference between the types of detectable gases is called the selectivity of the detector. The gas detectors with strong selectivity are limited by their own characteristics and are difficult to be widely used. Therefore, the detector used for VOCs detection should be a universal detector, the detection accuracy should be high, and the volume should be small, which is conducive to system integration and miniaturization design. In the detectors described above, the detection accuracy of FID is very high, but FID requires hydrogen as the combustion gas. The application range of ECD and ion migration spectrum detector is narrow, and it is not suitable for use as a VOCs detector. TCD has strong universality, but its low detection accuracy cannot achieve trace detection. Considering the characteristics of the above detectors, the photoionization detector is used as the terminal detector of the VOCs detection system [5].
In the early stage of the study, the UV light source and the ionization chamber were in the same space, which limits the sensitivity and accuracy of the detector. Later, as the research progressed, the scientists separated the two and made the detector more accurate. In practical work, the sensitivity of the photoionization detector is greatly influenced by the performance of the ionization chamber. After the introduction of the commercialized PID by HNU in 1976, companies such as RAE and Ion Science also introduced the PID detection devices [6]. However, these devices are complex in structure, lack scale production, are not competitive in the market, and cannot meet the requirements of trace detection. Recently, gas pollution is ubiquitous, and the research on PID is at a high level at home and abroad. The existing sensors still have the characteristics of large size, large power consumption, low efficiency, and high cost, and cannot meet the requirements for efficient portable detection [7].