Estimation of measurement uncertainty in the determination of orthophosphates in seawater by continuous flow analysis (CFA)

Phosphorus is the second most important limiting nutrient for the growth of autotrophic organisms in coastal and oceanic environments and is present in a wide range of chemical forms both dissolved and particulate. Within the dissolved inorganic fraction of phosphorus, orthophosphates are the so-called soluble reactive phosphorus. This nutrient, as a central element in coastal and oceanic biogeochemical cycles, is one of the compounds measured for the physico-chemical quality indices established by the Water Framework Directive 2000/60/EC and one of the characteristics to be measured in the Marine Strategy Framework Directive 2008/56/EC. In this work, an estimation of the measurement uncertainty in the determination of orthophosphates in seawater by continuous flow analysis, based on ISO 15681-2:2003, in the range of 10-150 mu g/L as P was carried out by means of a global model of uncertainty quantification from validation data. The results were coherent with previous interlaboratory comparisons of orthophosphates in seawater. Expanded uncertainty did not exceed 6.5 % in the entire range.