A dual phase gas diffusion-FIA system containing a tubular PTFE-membrane
was studied as a mean of producing gas samples for routine
15N/14N isotopic ratio mass spectrometry. The method is based on
Rittenberg's reaction; the ammonium sample is injected into a liquid alkaline
stream containing hypobromite and the N2 gas produced in the reaction
diffuses across a PTFE-membrane into a helium carrier stream which carries it
to the detector.
Initially here, the use of a tubular microporous PTFE-membrane as a device
for the preconcentration of samples in aqueous solutions was investigated.
The performance of such a membrane was studied under a variety of
operating conditions. A qualitative model of the membrane mechanism was
developed based on the diffusion transport of vapour away from the
contained liquid surface through the connected pore space. The dispersion
undergone by the sample in the GD-FIA system containing this
preconcentration unit was also studied and this FIA system was applied as a
practical device for the determination and speciation of aluminium in a river
The procedure for generating nitrogen gas involved optimisation of the
system parameters including the oxidation reaction step and the production
on-line of the chemicals used. The nitrogen gas was generated easily and
rapidly, allowing a sample throughput capability of the order of 20 h-1. The
system was applied to the determination of total nitrogen content in
agricultural sample prepared by the Kjeldahl digestion. The method offered
precision and accuracy comparable to those of the standard distillationtitration
procedure. Isotope ratios were determined with good precision and
means for obtaining accuracy comparable with established techniques were
It was also shown that the DPGD-FIA system can be readily adapted to enable different forms of nitrogen e. g. N02-, N03- and NH4+ to be determined.
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.