Determination of phosphate in freshwater samples by flow-injection with lucigenin chemiluminescence

Lucigenin chemiluminescence (CL) in conjunction with flow-injection analysis (FIA) is used for the determination of phosphate in freshwater samples. The procedure is based on the formation of molybdophosphoric heteropoly acid (MoP-HPA) by the reaction of phosphate and ammonium molybdate under acidic conditions. CL emission was observed as a result of oxidation of lucigenin in aqueous sodium hydroxide solution in the presence of MoP-HPA. Calibration was linear up to 500 µg L-1 (r2 = 0.9998; n = 8), with a detection limit (S/N = 3) of 0.95 µg L-1. An injection throughput of 120 h-1, and relative standard deviation (RSD; n = 4) of 1.3-3.2% were achieved in the concentration range studied. An on-line chelating column was used to remove interfering cations. The method was applied to freshwater samples, and the results (51 ± 1.0 - 107 ± 2.0 µg L-1) did not differ significantly from results obtained using a spectrophotometric method (52.5 ± 1.0 - 102 ± 2.0 µg L-1) at 95% confidence level (t-test).