Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2003
Publication Date: 11/2/2003
Citation: He, Z., Honeycutt, C.W. 2003. Reduction of protein interference by the addition of sodium dodecyl sulfate during orthophosphate determination. American Society of Agronomy Meetings. Denver, CO
Technical Abstract: In characterizing organic P (Po) by phosphatase hydrolysis, the quantity of hydrolysable Po is represented by the difference in orthophosphate (inorganic P, Pi) determined before and after enzymatic incubation. Therefore, precise determination of Pi is critical to the enzymatic hydrolysis approach. The strong acid conditions required for conventional molybdenum blue methods interfere with Pi determination due to rapid hydrolysis of many labile Po compounds and the precipitation of enzymes (proteins). The molybdenum blue method of Dick and Tabatabai (J. Environ. Qual. 1977, 6:82-85) reduces the errors pertaining to non-enzymatic hydrolysis of Po. We revisited the method, finding a higher absorption peak at 850 nm in addition to the reported peak at 700 nm. 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 of assay solution. Therefore, the readings at 850 nm improved the sensitivities of Pi determination by about 45%. The precipitation of enzymes during Pi determination was prevented by the addition of 2% SDS (sodium dodecyl sulfate) before color-forming reagents were added. This method modification provides increased sensitivity of Pi determination, thereby improving the accuracy of Po analysis by phosphatase hydrolysis.