The provision of high quality analytical data is an essential prerequisite for understanding the
biogeochemical cycling of nutrients in the aquatic environment. Due to the instability of samples
collected for nutrient determinations however, in situ analysis is preferred. This approach also allows
for high temporal and spatial resolution of the data and alteration of the sampling frequency to meet
local environmental needs. Chapter One describes the role of nitrogen species, particularly ammonia
and nitrate, in the aquatic environment, their sources, and possible environmental effects and
summarises analytical techniques for their determination. Solid state miniaturised detectors and their
suitability for in situ monitoring are also discussed.
The characterisation and evaluation of a miniature Ocean Optics PSD - 1000 spectrometer and its
suitability for field deployment is described in Chapter Two. Parameters investigated were optical
resolution, wavelength repeatability, photometric linearity and instrumental noise and drift. The
incorporation of the Ocean Optics PSD - 1000 miniature spectrometer into a gas diffusion Flow
Injection (Fl) manifold for the determination of ammonia in natural waters is detailed in Chapter Three.
Optimisation of the Fl parameters and analytical performance are discussed in detail. The development
of an immobilised pH indicator and adaptation to a laminar Fl manifold is also considered. Chapter Four
describes the use of the miniature spectrometer in a Fl manifold for the determination of nitrate and
nitrite, with analytical figures of merit detailed. The increased information potential of the spectrometer
(i.e. full spectral acquisition) facilitated the removal of the refractive index problem using dual
wavelength correction.
Miniaturisation and automation of the optimised nitrate manifold using micro-solenoid pumps and
LabView™ graphical programming is described in Chapter Five. Field deployment of the automated
system was assessed during a six week British Schools Exploring Society Expedition to Lesotho, S.
Africa (in which an intensive biogeochemical survey of the Sehlabathebe National Park was conducted)
and a three day campaign on the River Frome, Dorset, U.K. Chapter Six details the ion
chromatographic analysis of major anions and cations (including ammonium and nitrate) in precipitation
samples. Two sampling campaigns were conducted. One was at an urban site (Plymouth City Centre)
from 27/01/98 - 11/05/98, and the influence of aerosol source on the chemical composition of Plymouth
precipitation is discussed. The other involved the Austrian precipitation network and wet deposition
trends for nitrate, ammonium and sulphate are discussed. The multivariate analysis technique of PCA
was applied to both environmental datasets and the interpretation and merits of this statistical approach
are considered.
Date of Award | 1999 |
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Original language | English |
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Awarding Institution | |
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AUTOMATED FLOW INJECTION INSTRUMENTATION FOR MONITORING NITROGEN SPECIES IN NATURAL WATERS
COLES, S. P. (Author). 1999
Student thesis: PhD