Model compounds for the determination of organic and total phosphorus dissolved in natural waters

The choice of model compounds for checking the recovery of dissolved organic and total dissolved phosphorus in natural waters is discussed. Ten compounds were compared for their recovery in fresh and seawater. Four different oxidative procedures were used: acidic and alkaline persulfate oxidation, continuous flow UV irradiation and high-temperature combustion (HTC). Certain compounds have been shown to decompose when heated for moisture removal. Due to impurities and moisture, HTC is therefore suggested as a reference method for model compounds, assuming 100% recovery of organic phosphorus as phosphate. Full recovery is to be expected for the compounds in fresh water, but not for seawater. Matrix effects vary according to the oxidative method, with recoveries as low as 50% or less for certain compounds. It is therefore recommended that several model compounds should be used, at least one labile (phosphoenolpyruvate, glycerophosphate or riboflavin-5-phosphate) and one refractory (aminoethylphosphonic acid, phytic acid or phosphorylcholine chloride). The alkaline persulfate method can be recommended for marine waters.