A pressure-calibration method of wavelength modulation spectroscopy in sealed microbial growth environment

A new pressure-calibration method for calibrating the reduction of second harmonic (2f) amplitude caused by pressure broadening effect in sealed microbial growth environment is present. The new method combines with linewidth compensation and modulation depth compensation and makes the 2f amplitude accurately retrieve metabolic CO₂ in microbial growth. In order to verify the method, a simulation experiment is developed, in which the increasing CO₂ concentration leads to the increasing pressure. Comparing with the relation between the traditional 2f amplitude and gas concentration, there is a monotonous relation between the calibrated 2f amplitude and CO₂ concentration, particularly, a linear relation is present when the CO₂ concentration is replaced with the CO₂ particle number. In terms of microbial measurement, the growth of Escherichia coli is measured, and the culture bottle is sealed during the microbial growth process. The experimental results show that, comparing to the microbial growth retrieved by traditional 2f amplitude, the calibrated 2f amplitude can accurately retrieve microbial growth in sealed environment. (paper)