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 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 ?g/mL (aqueous solution) and to 1.2 ?g/mL P (MIBK). The sensitivity of the proposed method is 0.0078 ?g/mL (aqueous solution) and 0.0066 ?g/mL (MIBK). Predlozena je modifikovana spektrofotometrijska metoda za odredjivanje fosfora u uglju i pepelu od uglja preko bizmut-fosfor-molibdatnog kompleksa. Bizmut u kiseloj sredini sa fosfatom i molibdatom gradi veoma stabilan kompleks koji redukcijom sa askorbinskom kiselinom prelazi u plavo obojenje ("molibdensko plavo"). Molarni apsorpcioni koeficijent PBiMo kompleksa iznosi 1.66x104 dm3 mol-1cm-1 na 720 nm (vodeni rastvor) i 2.10x104 dm3 mol-1cm-1 na 670 nm (MIBK). Interferencije od prisutnih jona su u tolerantnim granicama (??2 %). Berov zakon vazi za koncentracije do 0.6 ?g/mL (vodeni rastvor) i za koncentracije do 1,2 ?g/mL (MIBK). Osetljivost predlozene metode iznosi 0,0078 ?g/mL (vodeni rastvor) i 0.0066 ?g/mL (MIBK).