Photochemical combustion of organic matter in sea water, for nitrogen, phosphorus and carbon determination
Armstrong, F.A.J. and Tibbitts, S. (1968) Photochemical combustion of organic matter in sea water, for nitrogen, phosphorus and carbon determination. Journal of the Marine Biological Association of the United Kingdom, 48 (1). pp. 143-152.
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A photochemical reactor, using a medium power mercury arc lamp for oxidation of organic matter in sea water, is described. The decomposition of some known compounds in distilled water and in sea water, using a 380 W lamp, was followed. First order kinetics with rate constants in the range 0.2-4.0 h-1 were observed. All the nitrogen compounds tested, including urea and some of its derivatives, were oxidized quantitatively. Breakdown of phosphorus compounds was rapid, but polyphosphate esters yielded polyphosphate ion which was only slowly hydrolysed to reactive orthophosphate. If polyphosphate is to be determined, hydrolysis by heating with acid should follow the irradiation. Some samples of English Channel water contained 0.02-0.05 ,ug-atom P/l. as organic polyphosphate. A technique is described for measuring oxygen consumption during irradiation. It provides a method for measuring total biological oxygen demand or an empirical carbon determination. The decomposition of naturally occurring organic compounds in sea water did not follow first-order reaction kinetics and rate constants declined to about one-fifth of their initial values as the reaction progressed. The times required for 98 % oxidation of carbon, nitrogen and phosphorus compounds in sea water were respectively 11, 12 and 5 h. Organic nitrogen determinations from some positions in the English Channel are given in graphical form. The fall in the range 2-9 (mean 5.1) ,ug-atom N/l., with little spatial or seasonal variation. There is nearly as much organic as inorganic nitrogen present in these waters.
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