A Highly Sensitive, Flow Through H2 Gas Analyzer for Use in Nitrogen Fixation Studies

Abstract

Studies of H₂ evolution by N₂ fixing systems are frequently limited by an inability to accurately measure H₂ gas concentrations of less than about 10 microliters per liter. In this study, a H₂ gas analyzer is described which is able to accurately and reproducibly detect up to 100 times lower H₂ concentrations than most thermal conductivity gas chromatographs or other conventional instruments used for the measurement of H₂ gas. This high level of sensitivity (maximum of about 0.02 microliter per liter H₂ per millivolt output) and the ability to continuously monitor H₂ concentration directly in a flowing gas stream, makes this instrument well suited for use in an open gas exchange system. Since the sensor used in the instrument was also sensitive to other combustible gases, it was necessary to demonstrate that H₂ was the only combustible gas produced by the N₂ fixing system being studied. When an air stream was passed through a pot containing nodulated soybean (Glycine max L.) roots, gas chromatographic analysis of the effluent gas stream revealed that H₂ was the only combustible gas present. These results were supported by other studies in which no combustible gases were detected in the effluent gas stream from soybean roots nodulated with USDA 110, a Rhizobium strain which displays active uptake hydrogenase activity.