Science Serving Maryland's Coasts
Patricia Glibert, Ph.D.
Horn Point Laboratory
Comparison and Specificity of Two Methods for Determining Urea in Estuarine Water
Direct and enzymatic methods for urea determination were compared and analyzed for specificity. Organic nitrogen compounds (arginine and humics) were added to urea standards to measure interference in both methods. In the enzymatic method, urea concentration appeared to decrease with increasing arginine concentration. However, minor ammonia contamination in the arginine stock solution created uncertainty as to these results. However, the presence of arginine appeared to have no effect on the direct method. In the presence of humic material, the enzymatic method underestimated true urea concentrations, but the direct method was not as significantly affected. Pursuing a peripheral issue led to the conclusion that the enzymatic method underestimates urea concentrations under saline conditions. Urea standards and Pocomoke River samples were assayed using both methods. The enzymatic method underestimated urea concentrations relative to the direct method. Culture studies with the brown tide organism Aureococcus anophagefferens indicated that arginine is not an effective substrate for the organism's urease.
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