U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
2005
Abstract
In characterizing organic phosphorus (Po) by phosphatase hydrolysis, the quantity of hydrolyzable Po is represented by the difference in orthophosphate [i.e., inorganic P (Pi)] determined after and prior to enzymatic incubation. Therefore, precise determination of Pi is of major importance for accurate application of the enzymatic hydrolysis approach. The strong acid conditions required for conventional molybdenum blue methods interferes with Pi determination due to rapid hydrolysis of labile Po and precipitation of enzymes (proteins). The molybdenum blue method of Dick and Tabatabai in 1977 reduced errors pertaining to nonenzymatic hydrolysis of Po. This study revisited the method, finding that the absorption coefficient at 850 nm was 45–49% higher than at 700 nm, and linear up to at least 80 nmol Pi in 1-mL assay solution. Therefore, adaptation of the readings at 850 nm improved the sensitivities of Pi determination by about 45%. Enzyme precipitation during Pi determination was prevented by addition of 2% sodium dodecyl sulfate (SDS) before color-forming reagents were added. This method modification provides increased sensitivity for Pi determination, thereby improving the accuracy of Po analysis by phosphatase hydrolysis.
Comments
Published in Communications in Soil Science and Plant Analysis, 36: 1373–1383, 2005. DOI: 10.1081/CSS-200056954