Colloidal material (0.001 - 1 um) in soil leachate and agricultural drainage waters is an important route for the transport of contaminants such as phosphorus from land to catchments. Excessive phosphorus concentrations can result in eutrophication of natural waters. To be able to characterise the colloidal material, in terms of size distribution, a mild and relatively new separation technique field-flow fractionation (FFF) can be used to fractionate complex colloidal samples. By combining FFF and flow injection analysis (FIA) more detailed physico-chemical information on phosphorus species in soil leachates and agricultural runoff waters can be obtained. Chapter 1 describes the methods used to determine phosphorus and also to characterise colloidal material, especially using FFF, and particularly focusing on the Flow FFF (FIFFF) sub-technique. Chapter 2 concentrates on the experimental considerations for FIFFF with recommended procedures for the setup and calibration of the system. In Chapter 3, SdFFF is used to compare the use of centrifugation and filtration for the fractionation of an Australian soil suspension, and demonstrates the uncertainties surrounding the use of conventional membrane filtration. FIFFF is used in Chapter 4 to optimise a sampling, treatment and preparation protocol for two contrasting soil types sampled in the UK. Centrifugation and filtration methods are also compared in a similar approach used in Chapter 3. In Chapter 5 a portable Fl monitor is optimised for the detection of reactive phosphorus. The linear range for the Fl monitor is determined as 0.8 - 8.0 uM PO4-P with a limit of detection o f 0.6 uM PO4-P. A digestion method is also optimised for the determination of total phosphorus using an acidic peroxydisulphate autoclaving method. In Chapter 6, FIFFF and FIA are combined in an experiment describing the fractionation of a soil suspension and the subsequent determination of phosphorus associated with different size fractions. The results from this combination show great potential and will help improve our understanding of the role of colloids in phosphorus transport from agricultural land to catchments.

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