Attention:

Certain features of Sigma-Aldrich.com will be down for maintenance the evening of Friday August 18th starting at 8:00 pm CDT until Saturday August 19th at 12:01 pm CDT.   Please note that you still have telephone and email access to our local offices. We apologize for any inconvenience.

Analytical Method: Ammonia (free)

Materials and reagents:
Cat.No. 100706 Spectroquant® Spectrophotometer Pharo 100
Cat.No. 100707  Spectroquant® UV/VIS Spectrophotometer Pharo 300
Cat.No. 114946 Rectangular cells 10 mm and/or
Cat.No. 114947 Rectangular cells 20 mm and/or
Cat.No. 114944 Rectangular cells 50 mm and/or
Cat.No. 173502 Semi-microcells 50 mm
Cat.No. 114752 Spectroquant® Ammonium Test
Cat.No. 114752 Spectroquant® Ammonium Test
pH-meter
Thermometer

Method:
Measurement of free ammonia under consideration of the pH and temperature of the sample after spectrophotometric determination of the ammonium content.
Evaluation acc. to Steffens (see the literature 1)).

Measuring range:
0.00 - 3.65 mg/l NH3    0.00 – 3.00 mg/l NH3-N   in the 10-mm rectangular cell
(method No. 2520)
0.00 - 1.83 mg/l NH3    0.00 – 1.50 mg/l NH3-N   in the 20-mm rectangular cell
(method No. 2521)
0.00 - 0.73 mg/l NH3    0.00 – 0.60 mg/l NH3-N   in the 50-mm rectangular cell
(method No. 2522)

Working instructions:
Sample preparation:
Measure the original pH and make a note of the result.
Measure the original temperature of the sample and make a note of the result (0 – 60 °C).
Adjust the pH of the sample to be analyzed to 4 – 13.
If the pH is <4 add sodium hydroxide solution dropwise, if the pH is >13 add diluted sulfuric acid dropwise until a pH value between 4 and 13 is achieved.
Heat the sample to be analyzed to a temperature of 20 – 30 °C.
 
Zeroing the photometer:
When these methods are used, the photometer must be zeroed each new working day. To do this call up the respective stored method 2520, 2521 or 2522 and fill the corresponding cell with distilled water or water for online analysis.
Subsequently press the BLANK ZERO key of the photometer and select “Zero photometer”. Insert the cell into the compartment to start the zeroing procedure.

Analysis:
The sample volume and the volume of the reagents must be doubled when making the measurements using the 50-mm rectangular cell. Alternatively you can use the 50-mm semi-microcell, Cat.No. 173502.

• Pipette 5.0 ml of sample into a test tube.
• Add 0.60 ml of reagent NH4-1 from the Cat.No. 114752 Spectroquant® Ammonium Test and mix.
• Add one level blue microspoon of reagent NH4-2 from the Cat.No. 114752 Spectroquant® Ammonium Test and shake vigorously until the reagent is completely dissolved.
• Leave to stand for 5 minutes.
• Add 4 drops of reagent NH4-3 from the Cat.No. 114752 Spectroquant® Ammonium Test and mix.
• Leave to stand for a further 5 minutes, then transfer the measurement sample into the corresponding cell
(10-mm, 20-mm, or 50-mm cell).

• Select method 2520 (10-mm cell), 2521 (20-mm cell), or 2522 (50-mm cell) on the photometer.
• The message “pH – please press START/ENTER to key in value” appears.
• Press START/ENTER, key in the noted pH, and acknowledge by pressing START/ENTER.
• The message “Next step: Temp – continue by pressing START/ENTER” appears.
• To key in the temperature press START/ENTER, key in the noted temperature of the sample, and acknowledge by pressing START/ENTER.
• The message “Next step: NH3 – continue by pressing START/ENTER” appears.

• Start the measurement by pressing START/ENTER.
NB: In the case that the photometer has not been zeroed, the message “Zero necessary” appears. Start the zeroing procedure by pressing the BLANK ZERO key of the photometer. Fill the corresponding cell with distilled water or water for on-line analysis. Insert the cell into the compartment to start the zeroing procedure.
• Insert the cell containing the measurement sample into the cell compartment.
• Insert the cell into the compartment to start the measurement. The measurement result in mg/l NH3 subsequently appears in the display of the photometer.
• The message “Next step: NH3-N – continue by pressing START/ENTER” appears.
• Press the START/ENTER key to start the conversion the measurement results. The measurement result in
mg/l NH3-N appears in the display.
• To start a new analysis press the START/ENTER key.

Note:
The measurement solution should be yellow-green to green in color.
Very high concentrations of ammonium in the sample produce a turquoise coloration of the measurement solution and lead to false-low results. In such cases a plausibility check of the measurement results should be run by diluting the sample (1:10, 1:100) with distilled water or water for analysis.

Literature:
1. Steffens, W.: 1981: Moderne Fischwirtschaft – Grundlagen und Praxis;
Verlag J. Neumann-Neudamm, Melsungen, Germany

 

Materials

     
Related Links

Categories