DETERMINATION OF ORTHOPHOSPHATE IN WATER BY SOLID-PHASE CHEMILUMINESCENT METHOD

Abstract

Phosphorus is one of the most important nutrients. Excessive content of its compounds in water objects leads to eutrophication, as well as reduces water quality. Methods based on the formation of molybdophosphate heteropolyacid (HPA) in an acidic medium with its subsequent reduction and spectrophotometric detection of the formed reduced "blue" HPA are most often used to determine phosphorus compounds. These methods are unsuitable for the analysis of waters with a phosphorus content <40 μg /L. The use of the chemiluminescent method (CL) makes it possible to increase the sensitivity of the determination, but CL detection in an acidic medium under the conditions of formation of HPA is limited by the existing indicator systems. To increase the selectivity of the method for determining the microquantities of phosphate relative to metal ions, we used an approach based on the adsorption removal of analyte with next determination using the CL method. Previous removal of phosphate from an aqueous solution in the form of reduced molybdostibiumphosphate HPA was released using batch technique in optimal conditions of its formation in the solution. Silica modified with cetyltrimethylammonium bromide was used as anion exchange adsorbent. Then the concentrate was processed with alkaline lucigenin solution and registration of the CL glow resulting from the reaction. Under optimal conditions of phosphate determination, the calibration curve is linear in the range from 3.7 to 147 μg PO43–/L with a detection limit of 0.8 μg PO43–/L. Cations K+, Na+, Fe(III), Mo(VI), NH4+ and anions Cl–, F–, HCO3–, С4Н4О62–, Asc–, NO2–, SO42–, as well as EDTA, do not interfere. Silicates (SiO32–) do not interfere with the determination of phosphate, even in 100-fold excess. Nitrates at concentrations below the average content in drinking water do not interfere with the determination. The developed technique was tested on a sample of pump room water. The technique is characterized by high sensitivity and a wide range of detectable concentrations. It is not inferior in sensitivity to flow methods using fluorescent or chemiluminescent detection.