Phosphate in Effluents

Photometric determination using the Phosphorus molybdenum blue method.

Introduction

Phosphorous is a key nutrient that must be kept within certain limits in the environment. In excess, it can upset aquatic ecosystems by encouraging excessive growth of algae and plants in a process termed eutrophication.1 As a result, testing phosphorous in effluents is critical from an environmental perspective. In this application note, we describe a determination of one form of phosphorous, phosphate, using photometry and Spectroquant^® Phosphate Test Kits.

Experimental Method

In sulfuric solution, orthophosphate ions react with molybdate ions to form molybdophosphoric acid. Ascorbic acid reduces this to phosphomolybdenum blue (PMB) that is determined photometrically. The method is analogous to EPA 365.2+3, APHA 4500-P E, and DIN EN ISO 6878.

Reagents, Instruments and Materials

Test Kits

One of the following test kits is necessary for this analysis:

• Phosphate Cell Test (o-phosphate and total phosphorous) Method: photometric, PMB 0.05 - 5.00 mg/l PO₄-P; 0.2 - 15.3 mg/l PO₄^3-; 0.11 - 11.46 mg/l P₂O₅ Spectroquant^® (1.14543)
• Phosphate Cell Test (o-phosphate and total phosphorous) Method: photometric, PMB 0.5 - 25.0 mg/l PO₄-P; 1.5 - 76.7 mg/l PO₄^3-; 1.1 - 57.3 mg/l P₂O₅ Spectroquant^® (1.14729),
• Phosphate Test (o-phosphate) Method: photometric, PMB 0.0025 - 5.00 mg/l PO₄-P; 0.0077 - 15.3 mg/l PO₄^3-; 0.0057 - 11.46 mg/l P₂O₅ Spectroquant^® (1.14848)

Instruments

One of the following instruments is necessary for this analysis:

• Spectroquant^® VIS Spectrophotometer Prove 100 (1.73016)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 (1.73017)
• Spectroquant^® UV/VIS Spectrophotometer Prove 600 (1.73018)
• Spectroquant^® Photometer NOVA 60A (1.09752)*
• Spectroquant^® Colorimeter Move 100 (1.73632)

* This analysis pertains to Nova 60A and all legacy Nova instruments (Nova 30 or Nova 60)

Materials

• Rectangular cells 10 mm (1.14946) and/or
• Rectangular cells 20 mm (1.14947) and/or
• Rectangular cells 50 mm (1.14944)

Procedure

• Sample preparation: Cloudy samples must be filtered before determination.

• Analysis: Determine with the above-mentioned test kits.

• Calculation: Phosphate content in mg/l PO₄-P = analysis value in mg/l PO₄-P

References

1. 2016. 1. European Environment Agency. Eutrophication. [Internet].[cited 18 Oct 2021]. Available from: https://www.eea.europa.eu/publications/signals-2000/page014