A COMPARISON OF METHODS FOR THE DETERMINATION OF DISSOLVED AND PARTICULATE PHOSPHORUS IN NATURAL-WATERS

A comparison of five methods used for the determination of dissolved t otal phosphorus (DTP) in natural waters is reported. The methods compa red different approaches to oxidizing organic-P compounds, and destroy ing polyphosphates to give forms available to standard colorimetric me thods. The methods used were ultraviolet (UV) irradiation, high-temper ature treatment with magnesium persulphate, autoclaving under acidic o r alkaline conditions, and magnesium nitrate oxidation. One series of experiments measured the oxidation efficiency of the methods when used with model organic-P compounds (phosphomonoesters, P-nucleosides, pol yphosphates, metaphosphates, and phosphonates) which were diluted in f resh and sea waters. The methods were also applied to four different m arine and fresh water samples containing naturally occurring dissolved organic-P and polymeric-P compounds. The five methods had on average a greater than 90% oxidation efficiency for phosphomonoesters, includi ng phospho-sugars and phosphonates. However, only the methods that inc lude a hydrolysis step were able to satisfactorily depolymerize polyph osphates and metaphosphates as well as destroy the nucleosides adenosi ne-5-triphosphate and guanosine-5 diphosphate. The highest DTP concent rations in the natural water samples were obtained by the magnesium ni trate oxidation method, whilst the lowest values were given by the UV irradiation technique, implying that this latter commonly used techniq ue can seriously underestimate DTP when resistant compounds represent a significant fraction of the DOP. Overall, the magnesium nitrate meth od was chosen as the best technique of those tested. In a slightly mod ified form the technique was used to determine particulate phosphorus in natural waters. Copyright (C) 1996 Elsevier Science Ltd