Errors in Molybdenum Blue Methods for Determining Orthophosphate in Freshwater. Stainton, M., P. Canadian Journal of Fisheries and Aquatic Sciences, 37(3):472-478, 1980.
Errors in Molybdenum Blue Methods for Determining Orthophosphate in Freshwater [pdf]Paper  abstract   bibtex   
Whole lakewater was spiked with carrier free 32PO4, filtered through a 0.45-μm membrane filter and the filtrate fractionated using G-25 Sephadex. Three molecular weight fractions incorcorporated 32P labeling, one of which was colloidal. This labeled filtrate was treated with several variations of the molybdenum blue method for measuring orthophosphate followed by molecular weight fractionation. All variations in the molybdenum blue method caused a significant loss of phosphorus from the colloidal fraction. Phosphorus originating from the colloidal fraction tested as orthophosphate giving an overestimate of the true orthophosphate present.

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