Samples are too acidic for phosphorus determination by ascorbic acid?

01 January 2020 1 5K Report

My soil samples have been acid digested using sulfuric acid. I want to determine the concentration of phosphorus of my samples, however every time I try to use the ascorbic acid method my samples do not turn blue, unlike the standards. Instead, the samples turn an orange color. I tried to do the malachite green method but my samples turn yellow. Is there any way to solve this?

Paul Milham

Please read Murphy and Riley's method. My recollection is the desireable H2SO4 concentration is about 0.4 (either M or N I don't recollect and have no literature on hand).

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