Improvement in the sensitivity of orthophosphate determination by controlling the self-reduction of excess ammonium molybdate followed by room temperature non-ionic mixed micelle cloud point extraction of anionic phosphomolybdenum blue for spectrophotometric determination

A rapid, selective and sensitive non-ionic surfactant based mixed micelle cloud point extraction (NI-MM-CPE) method is developed for the determination of ultratrace orthophosphate in natural water matrices. This method is based on the formation of anionic hydrophilic phosphomolybdenum blue (PMB) in presence of hydrazine due to the reduction of yellow 12-molybdophosphoric acid (12-MPA), which is derived by the reaction of orthophosphate with ammonium molybdate (AM) in acidic medium. Non-ionic mixed micelles, Triton X-114 and Triton X-45, are used to extract anionic PMB from aqueous solutions. Acid (H2SO4) and AM are so optimized to get negligible process blank, which is due to self-reduction of AM. Due to decrease in the process blank the S/N ratio is improved resulting in improved sensitivity. The coloured PMB complex is also pre-concentrated from 50 mL to 0.5 mL, which further enhanced the signal sensitivity. Due to the synergistic effect of both the phenomena, the LOD of the method is improved to 0.5 ng mL−1 using spectrophotometer. The method is applied to tap, ground and mineral water; and cool drink samples for the quantification of orthophosphate.