Spectrophotometric determination of phosphorus in coal and coal ash using bismuth-phosphomobybdate complex

A modified spectrophotometric method using the bismuth phosphomolybdate complex for the determination of phosphorus in coal and coal ash is suggested. Bismuth to- gether with phosphate and molybdate forms a very stable complex in acid medium which turns blue ("molibdenum blue") by reduction with ascorbic acid. The apparent molar ab- sorptivity of PBiMo is 1.6610 4 dm 3 mol -1 cm -1 at 720 nm and 2.1010 4 dm 3 mol -1 cm -1 at 670 nm isobutyl methyl ketone (MIBK). Interference caused by the ions present are within the tolerance limits (2 %). Beer's law is obeyed in the for concentration range to 0.6 g/mL (aqueous solution) and to 1.2 g/mL P (MIBK). The sesitivity of the proposed method is 0.0078 g/mL (aqueous solution) and 0.0066 g/mL (MIBK).