Automated Modification of the Molybdenum Blue Colorimetric Method for Phosphorus Determination in Soil Extracts

Abstract

A flow injection analysis (FIA) method capable of automation for molybdate reactive phosphorus (P) determination in soil extracts is described. Results obtained using this method in three soil extracts [calcium chloride (CaCl2), Olsen, and Mehlich I] were the same as those provided by the manual molybdate blue colorimetric method. Linear range extending to 2 mg P L−1, detection limits ranging from 6 to 26 µg L−1 depending on the soil extract, and accurate recoveries from P‐spiked samples were achieved. The sensitivity of the system was around 0.3 absorbance units per mg P L−1, and the sampling frequency was 72 samples h−1, higher than those described for most of the flow injection methods.