Lab practical 3 - Ammonia-nitrogen analysis Flashcards
How much of earths water is freshwater?
<0.01%
How much of earths land surface is covered by freshwater?
0.8%
Where does Ammonia-nitrogen pose the greatest threat?
surface water
What can Nitrogenous compounds affect freshwater?
Make it unsuitable for drinking and harm in stream biota
What is Ammonia (NH3)?
Unionised form, gas that readily dissolves in water, toxic to aquatic biota in very
small concentrations
What is ammonium (NH4+)?
Ionised form, usually as a salt that readily dissolves in water and much less toxic
than ammonia
What will Ammonia and Ammonium be like in aqueous solution?
exist in equilibrium
How does pH affect the direction of ammonia and ammonium in aqueous solution?
low pH equation to to right = more ammonium (vice versa)
What does TAN stand for? (ammonia-nitrogen practical)
Total ammonia nitrogen
What is the aim of the ammonia nitrogen practical?
determine TAN concentration in 4 samples from the River Dud
What are the four locations along the River Dud? (A B C D)
A- upper river below oak forest
B- upper river below town (different channel to A)
C- below confluence A and B below waste water treatment
D- lower river below golf course
Who produced the protocol for determining ammonia in water samples?
Keeney and Nelson 1982
How is our method for determining ammonia different from Keeney and Nelson’s?
sodium salicylate for phenol
what Equipment is needed for the Ammonia-nitrogen analysis?
- Spectrophotometer
- Water samples (labelled A-D)
- Water bath or dry bath
- 25 mL volumetric flasks (x6 for working standards and x4 for samples).
- Beakers
- Cuvettes
- DIW
- 60ml of Sodium salicylate-sodium nitroprusside reagent
- 20ml of EDTA solution
- 40ml of buffered hypochlorite reagent
- 50ml of working standard that contains 2 ug of NH4+-N mL-1
- 1 mL pipette (and pipette tips)
- 25ml measuring cylinder
- Labels and pens
- Micro-tubes for placing in the water bath
What reagents are needed for the ammonia nitrogen practical?
Sodium salicylate-sodium nitroprusside
Buffered hypochlorite
Ethylenediaminetetraacetic acid
Standard ammonium
Working standard
How do you prepare a working standard for the ammonium nitrogen practical?
dilute 4mL of the concentrated solution to 200 mL in a volumetric flask with DIW
What does DIW stand for?
di-ionised water
What volumes of working standard need to be pipetted to prepare the standards?(mL) (ammonia-nitrogen practical)
0
1
2
3
5
10
What dilutions need to occur to the working standard volumes to produces the standards? (ammonium-nitrogen)
25 mL to each flask
What will the concentrations of standards be in the ammonium nitrogen dilutions? (ug of NH4+-N)
0mL= 0 ug of NH4+-N
1ml= 2 ug of NH4+-N
2ml= 4 ug of NH4+-N
3ml= 6 ug of NH4+-N
5ml= 10 ug of NH4+-N
10ml= 20 ug of NH4+-N
What must you ensure to do with the beakers you have put the working standard dilutions in?
label the beakers 1-6 so the dilutions can be differentiated
After the working stock dilution what is the next step of the ammonia nitrogen procedure? (EDTA)
Add 1ml EDTA to 25 ml volumetric flasks for the dilutions and water samples and swirl to mix
After adding 1 ml EDTA to the dilutions and water samples what is added next? (ammonium nitrogen practical)
4 mL of salicylate-nitroprusside and then bring volume to 20ml with DIW
How much of each water sample should you put into the volumetric flasks? (ammonium nitrogen)
3ml of each added to flasks labelled A-D
Once the volume in the volumetric has been brought to 20ml what is added? (ammonia nitrogen practical)
2ml buffered hypochlorite and then immediately add DIW to take volume to 25ml
What must be added first to the volumetric flask to ensure proper colour change? (ammonia nitrogen practical)
salicylate-sodium nitroprusside reagent must be added before the buffered hypochlorite reagent
When the solutions of dilutions and water samples have been fully mixed in their individual flasks what do you do? (bath)(ammonia nitrogen practical)
transfer some of each solution into microcentrifuge, put in 37*c water bath for 30 mins
Why are the microcentrifuges with the dilutions and water samples put in a dry bath? (ammonia nitrogen practical)
for colour development
What do you do with the solutions after you take them out of the dry bath? (ammonia nitrogen practical)
Allow to cool
Put through spectrophotometer at 667nm (against DIW blank)
What did Nelson 1983 say about the colour stability of samples in the ammonia nitrogen practical?
stable for 4 hours
How long would it take for colour development of samples at room temp (23*c)? (ammonia nitrogen practical)
2 hours
How do you get the NH4+ concentrations in the samples? (ammonia nitrogen practical)
obtain equation by linear regression of standard concentration and corresponding absorbance
