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This article in JEQ

  1. Vol. 30 No. 6, p. 2206-2209
    Received: Oct 16, 2000

    * Corresponding author(s): edangelo@ca.uky.edu
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Rapid, Sensitive, Microscale Determination of Phosphate in Water and Soil

  1. Elisa D'Angelo *a,
  2. J. Crutchfieldb and
  3. M. Vandivierea
  1. a Univ. of Kentucky, Soil & Water Biogeochemistry Lab., Dep. of Agronomy, N-122 Agricultural Science Building North, Lexington, KY 40546-0091
    b Univ. of Kentucky, Analytical Services Lab., Dep. of Agronomy, S-104 Agricultural Science Building North, Lexington, KY 40546-0091


A rapid and sensitive analysis of inorganic and organic phosphorus (P) is needed to analyze water and soil extracts at submicromolar concentrations. The proposed method, based on the complexation of malachite green with phosphomolybdate under acidic conditions, was adapted to a 96-well microtiter plate format, and was tested for matrix interferences using 15 soils and some common extractants, including water, KCl, CaCl2, NaOH, and HCl. The accuracy of P determination was affected when CaCl2 and HCl concentrations were greater than 0.1 M and when NaOH concentration exceeded 0.4 M Potassium chloride concentration up to 1 M did not interfere with P determination. The molar absorptivity was 46841 M −1 cm−1 and the reagent blank absorbance was 0.071 ± 0.003 (n = 10). At the 99% confidence limit, the method detection limit was calculated to be 0.006 mg P L−1 Recovery of added inorganic P in different types of soils and extracts ranged between 95 and 112% with an average of 102%. The proposed microplate method allows P to be determined rapidly in a wide range of soil types and extracts and requires limited volume (20–200 μL). The procedure uses limited quantities (40 μL) of two stable reagents (>1 yr), and generates low amounts of hazardous waste.

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Copyright © 2001. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.30:2206–2209.