A simple vapour phase decomposition (VPD) of quartz powder in a polypropylene vessel and determination of phosphorus by spectrophotometry

A simple, low pressure, low temperature vapour phase decomposition (VPD) of quartz powder has been developed for the determination of phosphorus. A platinum dish containing the quartz or silicon powder was placed inside a polypropylene vessel containing 40 ml of 1:1 mixture of HF and HNO3. After capping the vessel, the entire assembly was heated on a water bath at ∼90 °C for 8 h. The platinum dish was removed from the vessel, the sample solution was treated with 0.5 ml of H2SO4 and 0.5 ml of HClO4 and was heated on a hot plate till HClO4 fumed out. The resultant solution was diluted to 40 ml (∼0.4N), analysed for phosphorus by spectrophotometry as an ion-pair of molybdophosphate with crystal violet. Phosphorus contamination by reagents has been drastically reduced (around 250 times) compared to the conventional dissolution procedure. The optimum reaction conditions were [H+]=0.42N, [H+]/Mo=62 for the formation of molybdophosphate and its extraction into n-butyl acetate. No interferences due to fluoride, silicate (active silica) and arsenic (V) upto 6.7×103, 2.7×103 and 2.0×103 times the content of phosphorus, respectively were observed. The LOD was found to be 0.066 μg g−1 (±3 s). RSD is 0.4–2.3% and the molar absorptivity is 2.7×105 l mole−1 cm−1.