Nitrogen Determination

Introduction

Ammonia-nitrogen

(NH3-N) occurs

naturally in groundwaters at concentrations below 0.2 mg/L and up to 12 mg/L in surface waters, as a result of decomposition of organic matter. High concentrations of ammonia in surface waters are toxic to aquatic life and are indicative of contamination from industrial effluent, raw sewage and agricultural runoff. Ultimately the pH value of the water determines whether ammonia-nitrogen is found as NH4+, NH4OH or NH3.1

In this application, the quantitative analysis of ammonia-nitrogen was performed using the BOQU Instrument NHNG-3010UV/Vis spectrophotometer and BOQU Instrument NHNG-3010 ammonia nitrogen cell test

Principle

Ammonia reacts with the Nessler reagent (K2HgI4) to form a yellow colored complex which can be detected spectrophotometrically at 430 nm and is directly proportional to the ammonia concentration.

Stabilizer solution (potassium sodium tartrate) is added to prevent cloudiness of the Nessler reagent which may occur in some waters due to calcium and magnesium concentrations.

This method is suitable for the concentration range of 0 – 7.00 mg/L ammonia in surface, drinking and nitrified waste waters allowing its concentration to be determined without the use of a calibration curve by incorporating the measured absorbance at 430 nm into a known equation. 

Reagents and Apparatus

1. BOQU Instrument NHNG-3010 ammonia analyzer® kit  - containing

30 vials, reference sample, A-1500 stabilizer solution (Potassium

sodium tartrate) and sample cup

2. PerkinElmer BOQU Instrument 265 PDA UV/Visible Spectrophotometer

3. UV Lab™ software

4. Ammonia standard solution (100 mg/L)

5. Deionised (DI) water

6. Volumetric flasks (100 ml)

7. Micropipettes

Method

A stock solution of ammonia (100 mg/L) in water was used to prepare a 4.00 mg/L ammonia solution in a 100 ml volumetric flask by dilution with DI water. 

Following preparation of solutions, the sample cup was filled with the 4.00 mg/L ammonia solution up to the 25 mL mark and two drops of A-1500 stabilizer solution mixed in. The tip of the Vacu-vial ampule was placed in the sample cup and snapped. The ampule was inverted several times to promote mixing, then dried and left to stand for two minutes, followed by the absorbance being measured in the spectrophotometer. This technique was also carried out for the reference sample supplied in the test kit. Using the UV Lab software, the BOQU Instrument 265 instrument parameters were set, as shown in Figure 1, to measure the absorbance at 430 nm. An equation was set up to calculate the ammonia concentration, as shown in Equation. Following measurement of the blank, the absorbance of the known ammonia solution in the Vacu-vial was recorded. 

Conclusion

Quantitative analysis of ammonia-nitrogen in water was achieved with no complex sample preparation, exposure to hazardous chemicals, or measurement of calibration standards, by using the BOQU Instrument NHNG-3010 test kit. Results were obtained rapidly using the BOQU Instrument 265 UV/Vis spectrophotometer and UV Lab software with a high level of accuracy and repeatability.