Malachite Green Method for Determining P Concentration in Diverse Matrices.

Two experiments were conducted to investigate the use of the malachite green (MG) colorimetric method for determining P concentrations in diverse matrices. The first experiment compared MG to the ascorbic acid (AA) method to assess the sequential extraction of P during fractionation analysis, while the second compared MG to inductively coupled plasma atomic emission spectroscopy (ICP-AES) for determining P in ammonium oxalate extracts (P_ox). The samples were sediments from the Walnut Creek watershed in Jasper County, Iowa. The results showed that the MG and AA methods agreed for determining P concentration in the extracts of water, 1 M HCl,  and concentrated H₂SO₄. However, there were small discrepancies between the two methods for extracts of 0.5 M NaHCO₃, 0.1 M NaOH, and concentrated HCl. For determining P_ox, the MG method resulted in significantly higher values than those obtained by ICP analysis.