Microbial denitrification is a fundamental reaction sequence within the global cycle of nitrogen that returns fixed nitrogen to its elementary state. In denitrification studies there is a need for an efficient gas analysis system that should meet the following requirements: (i) NO, NzO, N2 and O2 as one group of gases should be quantified in a single sample; (ii) quantitation should cover a wide range of gas concentrations; (iii) short intervals between successive determinations are required for kinetic measurements; and (iv) the sample volume should be small to keep changes in the reaction system negligible. Use of a sample loop is not possible because of this latter limitation.
Shortly after the introduction of porous polymer beads by Hollis', this material was adapted for gas determinations in denitrification studie9. Although this meant a substantial improvement over manometric methods, several limitations still had to be accepted: simultaneous analysis of the pertinent components for denitrification cannot be achieved within a sufficiently short time span, O2 and N2 are not separable and water causes straggling peaks on all types of porous polymers3. Molecular sieve, activated alumina or silica gel inorganic adsorbents show similar limitations when a simultaneous and rapid analysis is needed. Temperature programmes, including retooling cycles and dual detector systems, were developed but do not meet the above requirements for gas separation4+.
An isothermal multi-column system is the only alternative for taking advantage of different adsorbents and circumventing their undesirable features. Arrangements of multi-column systems for the analysis of gas mixtures as produced by denitrification have been tested previously. The time requirement for one determination', however, hampered fast kinetic studies, and straggling peaks of another column system* would interact with consecutive measurements.
This paper describes the design and performance of an isothermally operating dual-column system that rapidly separates Hz, 02, N2, NO, CO, N20 and CO2 and allows subsequent determinations within 3-min intervals.