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

Mihajlović Ranđel P. (Faculty of Science, University of Kragujevac, P. O. Box 60, YU-34000 Kragujevac)
Ignjatović Nataša R. (Faculty of Science, University of Kragujevac, P. O. Box 60, YU-34000 Kragujevac)
Todorović Marija R. (Faculty of Chemistry University of Belgrade, P. O. Box 158, YU-1001 Belgrade)
Holclajtner-Antunović Ivanka D. (Faculty of Physical Chemistry, University of Belgrade, YU-11001 Belgrade, Yugoslavia)
Kaljević Vesna M. (Faculty of Science, University of Kragujevac, P. O. Box 60, YU-34000 Kragujevac)

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 μg/mL (aqueous solution) and to 1.2 μg/mL P (MIBK). The sensitivity of the proposed method is 0.0078 μg/mL (aqueous solution) and 0.0066 μg/mL (MIBK).

Keywords: spectrophotomery, phosphorus determination, coal, coal ash, bismuth phosphomolybdate complex.