Photometric Determination of Ammonium in Compost Using the Indophenol Blue Method with Calcium Chloride Extraction

Abstract

This protocol describes the photometric determination of ammonium in compost using indophenol blue utilizing Spectroquant^® test kits and spectrophotometers. Ammonium ions are extracted from compost samples using a calcium chloride solution. The ions that were extracted are then mixed with hypochlorite ions to form monochloramine, which further reacts with a phenol compound to make a blue indophenol derivative which is then  measured photometrically.

Section Overview:

• Introduction
• Reagents, Instruments and Materials
• Experimental Procedure
• Analysis
• Calculation
• References

This application note details the photometric determination of ammonium in compost, using the indophenol blue method. Post the sample extraction and in a 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 phenol compound to form a blue indophenol derivative that is determined photometrically.

Reagents, Instruments and Materials

Ammonium Test Kits/Reagents

For the measurement, one of the following Spectroquant^® test kits is necessary:

• Spectroquant^® Ammonium Cell Test (1.14544)*
• Spectroquant^® Ammonium Cell Test (1.14558)
• Spectroquant^® Ammonium Cell Test (1.14559)
• Spectroquant^® Ammonium Test (1.14752)
• Spectroquant^® Ammonium Test (1.00683)

*not compatible with Move 100

Instrument(s) & Devices

For the measurement, one of the following Spectroquant^® photometers is necessary:

• Spectroquant^® VIS Spectrophotometer Prove 100 Plus (1.73026)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 Plus (1.73027)
• Spectroquant^® UV/VIS Spectrophotometer Prove 600 Plus (1.73028)
• Spectroquant^® Colorimeter Move 100 (1.73632)

Also, legacy systems

• Spectroquant^® Spectrophotometer Prove 100/300/600
• Spectroquant^® Photometer NOVA 30/60/60A

Software for Data transfer

• Optional Spectroquant^® Prove Connect to LIMS software package (Y.11086) to transfer your data into an existing LIMS system.

Instrument Accessories

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

Other Reagents and Accessories

• Calcium chloride dihydrate for analysis (1.02382)
• Water for analysis (1.16754)
• Charcoal activated for soil tests
• Folded filter

Experimental Procedure

Reagent Preparation

Dissolve 3.68 g of calcium chloride dihydrate for analysis with 1 L of water to prepare a 0.025 mol/L calcium chloride solution.

Sample Preparation

• In a glass bottle mix 50 g of a naturally moist sample, free from coarse stones, with 100 mL of the calcium chloride solution.
• Add 1 spatula-tip full of activated charcoal for soil tests and shake the closed bottle in a shaking machine for 1 hour (alternative: stir in a beaker).
• Let the suspension settle and filter through a folded filter.
• For the determination of the water content, dry a similar sample to constant weight in the drying kiln at 105 °C. Drying of the sample before the determination is not advisable because of the fast change in the nitrogen forms.
• The analysis should take place very quickly.
• Storing the sample in plastic bags at room temperature changes the analysis values after a short time already.

Analysis

Determine with one of the above-mentioned test kits.

Calculation

Ammonium content in mg/kg NH₄⁺ = analysis value in mg/L NH₄⁺ x 2

See more applications for photometry at Protocols and Application Notes