388
P. J. Worsfold . E. P. Achterberg· A. R. Bowie . R. Sandford· V. Cannizzaro· P. Gardolinski
• A pathway must exist for the formation of the electronically excited state.
• The excited state must be capable of deactivation by the emission of radiation or
energy transfer to a fluorophore.
There are empirical guidelines for predicting CL behaviour. For instance, if an
analyte itself or an oxidation product is fluorescent, then oxidation of the molecule
may produce CL. There are, however, many exceptions to this principle, and in many
cases, CL reactions cannot be predicted. Nonetheless, many solution phase CL reactions involve the oxidation of aromatic substances. One of the most commonly used
is the reaction involving the oxidation of luminol (5-amino-2,3-dihydrophthalazine1,4-dione or 5-aminophthalhydrazide), an acyl hydrazide, in basic solution (pH 10-11).
The reaction is catalysed by haeme-containing enzymes (e.g. peroxidase) and several
metal ions of which Co(Il), Cu(II) and Fe(II) are particularly effective. In addition,
hexacyanoferrate(III) can act as catalyst/co-oxidant in the reaction. Due to the rapid
and transient CL emission from this reaction, it is ideally suited to incorporation within
an FI manifold.
16.1.3
Spectrophotometric Detection
Spectrophotometry was the first detection system used in conjunction with FI (Ruzicka
and Hansen 1981) and remains the most popular in terms of applications and published papers. The determination of nutrients in natural waters is the most common
environmental application of the technique. In recent years, the advent of solid-state
detectors has made FI -SPEC a viable system for deployment in the field, including
shipboard use. Its compact nature means that it can also be deployed as a submersible
device when incorporated in a suitable housing. This provides the possibility of autonomous operation at remote sites for days, or even weeks at a time, which would
give high temporal data resolution during transient events such as storms.
16.2
FI-CL Determination of Iron in Sea Water
16.2.1
Marine Chemistry of Iron
Iron (Fe) is the fourth most abundant element in the Earth's crust (-5.6%), but like
other reactive trace elements, dissolved Fe levels in open-oceanic waters are often subnanomolar. The marine biogeochemistry of Fe is complicated by its redox speciation,
low solubility and involvement in biological cycles. Improvements to the understanding of the redox cycling of Fe are required, and chemical nature of Fe associated with
various operationally defined parameters (e.g. labile, dissolved, colloidal, organically
bound, particulate) needs further clarification.
The major sources of Fe to the world's oceans are atmospheric, fluvial, hydrothermal, and continental shelf regeneration and upwelling of Fe-enriched subsurface waters. In remote areas, the ocean receives the majority of surface water Fe from atmospheric dusts, and the true impact of suspended aerosols on trace element levels can
P. J. Worsfold . E. P. Achterberg· A. R. Bowie . R. Sandford· V. Cannizzaro· P. Gardolinski
• A pathway must exist for the formation of the electronically excited state.
• The excited state must be capable of deactivation by the emission of radiation or
energy transfer to a fluorophore.
There are empirical guidelines for predicting CL behaviour. For instance, if an
analyte itself or an oxidation product is fluorescent, then oxidation of the molecule
may produce CL. There are, however, many exceptions to this principle, and in many
cases, CL reactions cannot be predicted. Nonetheless, many solution phase CL reactions involve the oxidation of aromatic substances. One of the most commonly used
is the reaction involving the oxidation of luminol (5-amino-2,3-dihydrophthalazine1,4-dione or 5-aminophthalhydrazide), an acyl hydrazide, in basic solution (pH 10-11).
The reaction is catalysed by haeme-containing enzymes (e.g. peroxidase) and several
metal ions of which Co(Il), Cu(II) and Fe(II) are particularly effective. In addition,
hexacyanoferrate(III) can act as catalyst/co-oxidant in the reaction. Due to the rapid
and transient CL emission from this reaction, it is ideally suited to incorporation within
an FI manifold.
16.1.3
Spectrophotometric Detection
Spectrophotometry was the first detection system used in conjunction with FI (Ruzicka
and Hansen 1981) and remains the most popular in terms of applications and published papers. The determination of nutrients in natural waters is the most common
environmental application of the technique. In recent years, the advent of solid-state
detectors has made FI -SPEC a viable system for deployment in the field, including
shipboard use. Its compact nature means that it can also be deployed as a submersible
device when incorporated in a suitable housing. This provides the possibility of autonomous operation at remote sites for days, or even weeks at a time, which would
give high temporal data resolution during transient events such as storms.
16.2
FI-CL Determination of Iron in Sea Water
16.2.1
Marine Chemistry of Iron
Iron (Fe) is the fourth most abundant element in the Earth's crust (-5.6%), but like
other reactive trace elements, dissolved Fe levels in open-oceanic waters are often subnanomolar. The marine biogeochemistry of Fe is complicated by its redox speciation,
low solubility and involvement in biological cycles. Improvements to the understanding of the redox cycling of Fe are required, and chemical nature of Fe associated with
various operationally defined parameters (e.g. labile, dissolved, colloidal, organically
bound, particulate) needs further clarification.
The major sources of Fe to the world's oceans are atmospheric, fluvial, hydrothermal, and continental shelf regeneration and upwelling of Fe-enriched subsurface waters. In remote areas, the ocean receives the majority of surface water Fe from atmospheric dusts, and the true impact of suspended aerosols on trace element levels can