A combined CDB-MAGIC method for the determination of phosphorus associated with sedimentary iron oxyhydroxides

A combined CDB-MAGIC method for the determination of sedimentary Fe-oxyhydroxide-bound P in citrate–dithionite–bicarbonate (CDB) reducing solutions is described. Quantitative removal of P from solution is accomplished through the alkaline precipitation of Mg(OH)2 (brucite) with 10 M NaOH. After subsequent separation by centrifugation and two washings with 10% NH4OH, the precipitate is re-dissolved in 10% HCl. The P concentration in the sample is subsequently measured by the conventional molybdate blue technique using a UV–vis spectrophotometer. The detection limit of the method is 1.2 μM with precision within 1.3–8.1% in the 6–30 μM P concentration range. The results obtained using the CDB-MAGIC protocol were equivalent to those obtained using ICP-AES (r2 = 0.860; p less-than-or-equals, slant 0.001; n = 29; with a linear slope of 1.19 ± 0.09). The CDB-MAGIC method provides then a simple, low cost alternative to the current methods based on ICP quantification.