Ammonium in Effluents With High COD Value

Photometric determination using the indophenol blue method.

Introduction

Ammonium is a key parameter in water testing, as it can have adverse effects on marine ecosystems if it is at high levels. One major issue is eutrophication, excessive plant and algal growth.¹ As a result, determining ammonium levels in effluents is a critical to maintaining aquatic environments. In this application note, ammonium is quantified in effluents with high chemical oxygen demand (COD) using the Spectroquant^® photometric system with ammonium test kits.

As the decomposition with the Crack-Sets 10 or 10C (Potassium peroxodisulfate) fails with strongly organic loaded water (criteria: COD content >300mg/l), a pre-decomposition to destroy the organic matrix is advisable, as described below.

Experimental Method

Ammonium nitrogen (NH₄-N) occurs partly in the form of ammonium ions and partly as ammonia. A pH-dependent equilibrium exists between the two forms. In strongly alkaline solution ammonium nitrogen is present almost entirely as ammonia, which reacts with hypochlorite ions to form monochloramine. This in turn reacts with a substituted phenol to form a blue indophenol derivative that is determined photometrically. Due to the intrinsic yellow coloration of the reagent blank, the measurement solution is yellow-green to green in color.

The method is analogous to EPA 350.1, APHA 4500-NH3 F, ISO 7150-1, and DIN 38406-5.

Reagents, Instruments and Materials

Test Kits

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

• Spectroquant^® Ammonium Cell Test method: photometric 0.010 - 2.000 mg/l NH₄-N; 0.01 - 2.58 mg/l NH₄⁺ (1.14739)
• Spectroquant^® Ammonium Cell Test Method: photometric 0.20 - 8.00 mg/l NH₄-N; 0.26 - 10.30 mg/l NH₄⁺ (1.14558)
• Spectroquant^® Ammonium Cell Test Method: photometric 0.5 - 16.0 mg/l NH₄-N; 0.6 - 20.6 mg/l NH₄⁺ (1.14544)*
• Spectroquant^® Ammonium Cell Test Method: photometric 4.0 - 80.0 mg/l NH₄-N; 5.2 - 103.0 mg/l NH₄⁺ (1.14559)
• Spectroquant^® Ammonium Test Method: photometric 0.010 - 3.00 mg/l NH₄-N; 0.013 – 3.86 mg/l NH₄⁺ (1.14752)
• Spectroquant^® Ammonium Test Method: photometric 2.0 - 150 mg/l NH₄-N; 2.6 - 193 mg/l NH₄⁺ (1.00683)

*not compatible with Move 100

Instruments

One of the following instruments is necessary for this analysis:

• Spectroquant^® VIS Spectrophotometer Prove 100 (173016)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 (173017)
• Spectroquant^® UV/VIS Spectrophotometer Prove 600 (173018)
• 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)
• Sulfuric acid 95 -97% (1.00731) for analysis
• Sodium hydroxide solution 32% (1.05590) for analysis
• Hydrogen peroxide (Perhydrol^®) 30% (1.07209) for analysis
• Water for analysis (1.16754)

Sample Preparation

• Evaporate 100 ml of sample and 5 ml of sulfuric acid 95 - 97 % in a 600 ml glass beaker to about 10 ml.
• Mix this mixture cautiously with 5 ml Perhydrol^® 30% and heat.
• After some time when heavy reaction (gas formation, foaming) has faded, heat until SO₃-formation starts.
• If the solution turns brown or dark, let it cool down and add again 5 ml Perhydrol^® 30%.
• Once more heat until beginning SO₃-formation.
• If the solution stays colorless or light yellow, let it cool down, and dilute with about 50 ml distilled water and neutralize the solution with about 14 - 15 ml sodium hydroxide solution 32% to pH 4 - 6 using a pH - meter.
• After cooling transfer the solution into a 100-ml volumetric flask and fill up to volume with distilled water and mix.
• Ammonium will be fixed as ammonium sulfate in the solution and after the oxidation of the digestion can be measured with the above-mentioned test kits.

Analysis

Determine with the above-mentioned test kits.

Calculation

Ammonium content in mg/l NH₄-N = analysis value in mg/l NH₄-N