Qi Hongchao, Zhao Xinyu, Xu Yufu, Yang Ling, Liu Junjun, Chen Ke
School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian, Liaoning 116024, China.
Purification Equipment Research Institute of CSIC, Handan, Hebei 056004, China.
Anal Chem. 2024 Apr 2;96(13):5258-5264. doi: 10.1021/acs.analchem.3c05936. Epub 2024 Mar 19.
A rapid photoacoustic (PA) exhaust gas analyzer is presented for simultaneous measurements of nitrogen dioxide (NO) and sulfur dioxide (SO). A laser diode (LD) emitting at 450 nm and a light-emitting diode (LED) with a peak wavelength of 275 nm operated simultaneously, producing PA signals of NO and SO, respectively. The LD and LED were modulated at different frequencies of 2568 and 2570 Hz, and their emission light beams were transmitted through two resonant tubes in a differential PA cell (DPAC), respectively. A self-made dual-channel digital lock-in amplifier was used to realize the simultaneous detection of dual-frequency PA signals. Cross interference between the PA signals at the two different frequencies was reduced to 0.02% by using a lock-in amplifier. In order to achieve a rapid dynamic measurement, gas sampling was accelerated by an air pump. The use of mufflers and the differential PA detection technique significantly reduced the gas sampling noise. When the gas flow rate was 1000 sccm, the response time of the PA dual-gas analyzer was 8 and 17 s for NO and SO, respectively. The minimum detection limits of NO and SO were 1.7 and 26.1 ppb when the averaging time of the system was 10 s, respectively. Due to the wide spectral bandwidth of the LED, NO produced an interference to the detection of SO. The interference was reduced by the precise detection of NO. Since the radiations of the LD and LED passed through two different PA tubes, the impact of NO photochemical dissociation caused by UV LED luminescence on NO gas detection was negligible. The sharing of the PA cell, the gas lines, and the signal processing modules significantly reduced the size and cost of the PA dual-gas analyzer.
本文介绍了一种用于同时测量二氧化氮（NO）和二氧化硫（SO）的快速光声（PA）废气分析仪。一个发射波长为450 nm的激光二极管（LD）和一个峰值波长为275 nm的发光二极管（LED）同时工作，分别产生NO和SO的光声信号。LD和LED分别以2568 Hz和2570 Hz的不同频率进行调制，它们的发射光束分别通过差分光声池（DPAC）中的两个共振管。使用自制的双通道数字锁相放大器实现对双频光声信号的同时检测。通过使用锁相放大器，两种不同频率的光声信号之间的交叉干扰降低到了0.02%。为了实现快速动态测量，通过气泵加速气体采样。消声器的使用和差分光声检测技术显著降低了气体采样噪声。当气体流速为1000 sccm时，光声双气体分析仪对NO和SO的响应时间分别为8 s和17 s。当系统平均时间为10 s时，NO和SO的最低检测限分别为1.7 ppb和26.1 ppb。由于LED的光谱带宽较宽，NO对SO的检测产生了干扰。通过对NO的精确检测，这种干扰得到了降低。由于LD和LED的辐射通过两个不同的光声管，紫外LED发光引起的NO光化学解离对NO气体检测的影响可以忽略不计。光声池、气体管路和信号处理模块的共享显著减小了光声双气体分析仪的尺寸和成本。
