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

A modified spectrophotometric method using the bismuth phosphomolybdate complex for the determination of phosphorus in coal and coal ash is suggested. Bismuth together 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 absorptivity of PBiMo is 1.66x104 dm3 mol-1cm-1 at 720 nm and 2.10x104 dm3 mol-1cm-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 mg/mL (aqueous solution) and to 1.2 mg/mL P (MIBK). The sesitivity of the proposed method is 0.0078 mg/mL (aqueous solution) and 0.0066 mg/mL (MIBK).