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

Abstract

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 (r ²= 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).

Keywords:

• flow-injection analysis
• chemiluminescence
• lucigenin
• molybdate
• phosphate
• freshwater samples

Acknowledgements

The authors are grateful to the Higher Education Commission of Pakistan for financial support in the form of an Indigenous PhD Scholarship (PIN-042-210 012-Ps2-323).