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Octan-I-ol Extraction of Molybdophosphoric Acid in the Colorimetric Determination of Orthophosphate¹

ABSTRACT

A method for the analysis of orthophosphate in aqueous solutions is described. The detection limit of the method is <0.1 µg orthophosphate P, and the molybdophosphoric acid can be concentrated at least 300 times by extraction into octan-I-ol. The complex is reduced to the colored form after extraction into octan-I-ol and Beer's Law is obeyed at least to an absorbance value of 1.5. A study of the effects of temperature, shaking time and rate, and the organic to aqueous ratio on the extraction of molybdophosphoric acid was carried out. The extinction coefficient for the method was 22,000 liters mole^-1 cm^-1. Possible interference by various cations and anions in the determination was investigated and the technique was used successfully to analyze for phosphate in calcium chloride extracts from soil.

¹ Joint contribution from the Dep. of Soils and Plant Nutrition, Univ. of California, Davis, CA 95616, and the N.S.W. Dep. of Agriculture.

² Research Officer, N.S.W. Dep. of Agriculture, Agric. Res. Ctr., Wollongbar, N.S.W., 2480, formerly Research Assistant, Univ. of California, Davis, and Lecturer in Soils, Univ. of California, Davis.

Received for publication October 28, 1974. Accepted for publication October 23, 1975.