Novel calibration method for mass spectrometers for on-line gas analysis. Set-up for the monitoring of a bacterial fermentation

Abstract

A set-up procedure for the minimisation of signal noise of a capillary inlet mass spectrometer system, enabling direct use of data without noise ®ltering or drift correction, is described. A reliable calibration method was developed, involving standard calibration mixtures determined by the extreme vertices design. This novel method was shown to be the most accurate in comparison with a number of commonly used methods. These procedures enabled reliable on-line fermenter headspace gas analysis. With a relatively inexpensive mass spectrometer, monitoring of a fermentation and accurate estimation of oxygen uptake rate, carbon dioxide evolution rate, respiratory quotient and biomass concentration was possible.

Analysis of biological wastewater treatment processes using multicomponent gas phase mass balancing

“…The gas mixture of known composition was generated using the calibration mass¯ow controllers depicted in Figure 1. Ferreira et al (1998) found that this regression method produced excellent results in their work on OUR in fermentations, and it was believed that this method would be useful in the validation of the intensity ratio methodology.…”

“…The intensity ratio method was compared with an alternative approach, based on that of Ferreira et al (1998). This method involved producing an intensity± concentration calibration curve of the mass spectral signals over a narrow concentration range.…”

“…Equation 12 only requires determination of the mass¯ow of the target gas into the reactor and the inlet and outlet intensity ratios in order to determine the production/consumption rate within the reactor. Ferreira et al (1998) have found that the ®rst assumption stated above is not correct over a wide concentration range. However, this assumption can be used with good accuracy by calibrating the mass spectrometer signal over a narrow range, provided it spans the experimental range of the signal generated by the reactor off-gas.…”

“…One of the main differences of laboratory scale reactors for wastewater process investigations is the method used for mixing. Most aerobic full-scale systems obtain their mixing energy solely from aeration gas bubble motion through the liquid phase (Metcalf and Eddy et al, 1991), whereas in laboratory scale respirometric systems, mechanical stirrers usually provide some, if not all, of the energy imparted to the liquid (Ferreira et al, 1998;Spanjers, 1993;Sperandio and Paul, 1997;Oeggerli et al, 1995;Blok, 1974). This may appear to be of little consequence for many studies, but when hydrodynamics and¯uid shear have the potential to affect the results, consideration should be given to this aspect of reactor design.…”

“…At laboratory scale, such off-gas analysis techniques have been used for the measurement of oxygen uptake rate (e.g., Oeggerli et al, 1995;Ferreira et al, 1998), carbon dioxide production rate (Sperandio and Paul, 1997), and volatile organics Wanner et al, 1994). On a larger scale, this methodology has been applied, within the wastewater treatment industry, mainly to the measurement of oxygen transfer rates (Harris et al, 1996;Fujie et al, 1994;Mueller and Boyle, 1988;Redmon et al, 1983).…”