Optimization of the Analytical Method for Determining Phosphates in Detergents and Laundry Effluents

Abstract

Phosphate presence in natural water bodies may have a destructive effect on water ecology due to an excessive growth of plants. Detergents together with fertilizers are one of the greatest sources of phosphates as pollutants. The paper shows optimum conditions for a spectrophotometric determination of phosphates in detergents and effluents of laundries with the reagent ammonium molybdate tetrahydrate. In view of a large range of phosphate concentration in given specimens and a noticeable influence of the stock solution on the determination, it was necessary to modify the whole measuring method and carry out the validation procedure of the method. The characteristics of the method were determined (linearity, accuracy and precision, limit of detection and limit of quantification). The EDTA quantity, which causes disturbances in the spectrophotometric determination of phosphates using the method of molybdenum laundry bluing, was determined. Several methods for the preparation of a sample of powder detergent for the spectrometric determination of phosphates were studied: direct determination of phosphates from the detergent solution, determination of phosphates after the hydrolysis of sodium triphosphate with acides and determination of phosphates after oxidative degradation with H2SO4 and H2O2. A detergent of a well known composition (ECE Color Fastness Test Detergent 77) was used as standard detergent.