Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK.
Anal Bioanal Chem. 2019 Jul;411(17):3777-3787. doi: 10.1007/s00216-019-01877-0. Epub 2019 May 20.
Photoacoustic spectroscopy in a differential Helmholtz resonator has been employed with near-IR and red diode lasers for the detection of CO, HS and O in 1 bar of air/N and natural gas, in static and flow cell measurements. With the red distributed feedback (DFB) diode laser, O can be detected at 764.3 nm with a noise equivalent detection limit of 0.60 mbar (600 ppmv) in 1 bar of air (35-mW laser, 1-s integration), corresponding to a normalised absorption coefficient α = 2.2 × 10 cm W s. Within the tuning range of the near-IR DFB diode laser (6357-6378 cm), CO and HS absorption features can be accessed, with a noise equivalent detection limit of 0.160 mbar (160 ppmv) CO in 1 bar N (30-mW laser, 1-s integration), corresponding to a normalised absorption coefficient α = 8.3 × 10 cm W s. Due to stronger absorptions, the noise equivalent detection limit of HS in 1 bar N is 0.022 mbar (22 ppmv) at 1-s integration time. Similar detection limits apply to trace impurities in 1 bar natural gas. Detection limits scale linearly with laser power and with the square root of integration time. At 16-s total measurement time to obtain a spectrum, a noise equivalent detection limit of 40 ppmv CO is obtained after a spectral line fitting procedure, for example. Possible interferences due to weak water and methane absorptions have been discussed and shown to be either negligible or easy to correct. The setup has been used for simultaneous in situ monitoring of O, CO and HS in the cysteine metabolism of microbes (E. coli), and for the analysis of CO and HS impurities in natural gas. Due to the inherent signal amplification and noise cancellation, photoacoustic spectroscopy in a differential Helmholtz resonator has a great potential for trace gas analysis, with possible applications including safety monitoring of toxic gases and applications in the biosciences and for natural gas analysis in petrochemistry. Graphical abstract.
在静态和流动池测量中，使用近红外和红色二极管激光器，在差分亥姆霍兹谐振器中进行光声光谱学，以检测 1 巴空气中的 CO、HS 和 O/N2 和天然气，检测限为 0.60 mbar（600 ppmv）。用红色分布式反馈（DFB）二极管激光器，在 1 巴空气（35mW 激光，1s 积分）中可以检测到 764.3nm 的 O，归一化吸收系数α=2.2×10cmW s。在近红外 DFB 二极管激光器的调谐范围内（6357-6378cm），可以访问 CO 和 HS 吸收特征，1 巴 N2 中的 CO 检测限为 0.160mbar（160ppmv），30mW 激光，1s 积分），归一化吸收系数α=8.3×10cmW s。由于吸收较强，在 1 巴 N2 中，HS 的检测限在 1s 积分时间内为 0.022mbar（22ppmv）。类似的检测限适用于 1 巴天然气中的痕量杂质。检测限与激光功率呈线性关系，与积分时间的平方根呈线性关系。在 16 秒的总测量时间内，例如，通过光谱线拟合程序，获得 CO 的噪声等效检测限为 40ppm。已经讨论了由于弱水和甲烷吸收引起的可能干扰，并且已经证明这些干扰要么可以忽略不计，要么易于校正。该装置已用于微生物（大肠杆菌）半胱氨酸代谢中 O、CO 和 HS 的原位同时监测，以及天然气中 CO 和 HS 杂质的分析。由于固有信号放大和噪声消除，差分亥姆霍兹谐振器中的光声光谱学在痕量气体分析中具有很大的潜力，可能的应用包括有毒气体的安全监测以及在生物科学中的应用，以及在石油化工中的天然气分析。
