A REEXAMINATION OF THE MEASUREMENT OF DISSOLVED ORGANIC PHOSPHORUS IN SEAWATER

The standard UV irradiation and autoclave-promoted persulphate oxidation methods for the determination of dissolved organic phosphorus in seawater have been re-evaluated and tested against a new method which incorporates both the UV and persulphate oxidation methods. It was found that the UV irradiation and autoclaving times commonly used with the standard methods did not fully release the dissolved organic phosphorus in open-ocean surface seawater. Extending the UV irradiation period and the autoclaving time gave improved results. With these modifications, the persulphate technique was found to be 87±8% and the UV technique 90±6% efficient relative to the combination method in liberating organically bound phosphorus from a wide variety of seawater samples. However, repeated measurements of a Gulf Stream surface seawater sample using the combination method gave values 1.25-1.5 times higher than the modified persulphate and UV techniques separately. Seawater samples were also ultra-filtered into < 10 000 and > 10 000 molecular weight fractions and measured for dissolved organic phosphorus by the combination technique. The high molecular weight or colloidal fraction was found to comprise 20-50% of the total dissolved organic phosphorus. © 1990.