Simultaneous Determination of Various Phosphates in Water-Soluble Ammonium Polyphosphate

Abstract

Based on ion chromatography, this study developed a rapid method for simultaneous determination of linear polyphosphates (PPs) of orthophosphate (P1), pyrophosphate (P2), trimetaphosphate (P3m), tripolyphosphate (P3), tetraphosphate (P4), pentaphosphate (P5), and hexaphosphate (P6) in water-soluble ammonium polyphosphate (WAPP). Investigation indicated that the retention of PPs in column was endothermic and cooling column benefited the elution of PPs. With adjusting the elution mode, eluent (KOH) concentration, gradient time, flowrate, and column temperature, the optimized results were as follows: the injection volume of sample was 1.3 μL, column temperature was 30 °C, and flowrate of the eluent was 1.2 ml min−1. The linear equations for six phosphates are: y = 0.011cP1 + 0.021 (r = 0.9998), y = 0.012cP2 + 0.023, y = 0.011cP3m − 0.013 (r = 0.9997), y = 0.12cP3 + 0.017 (r = 0.9999), y = 0.011cP4 + 0.004 (r = 0.9983), y = 0.011cP5 − 0.082 (r = 0.9962), and y = 0.013cP6 − 0.029 (r = 0.9989), respectively. The determination ranges are: 1–500 mg L−1 for P1, P2, P3m, and P3; and 1–100 mg L−1 for P4, P5, and P6. The recovery is in the range 95–104% for P1, P2, P3m, P3, P4, P5, and P6; the detection limit is in the range 0.17–0.54 mg L−1 and RSDs of intra- and inter-day determination are 0.56–2.51% (n = 5) for seven PPs, and the analysis period is 15 min. The method was consistent with both gravimetric method and molybdenum blue method, while the RSD was in the range 0.61–1.87%. This rapid method can be applied in the determination of total phosphorus and various phosphates in PPs.