Lab practical 3 - Ammonia-nitrogen analysis

Question 1

How much of earths water is freshwater?

Answer 1

<0.01%

Question 2

How much of earths land surface is covered by freshwater?

Answer 2

0.8%

Question 3

Where does Ammonia-nitrogen pose the greatest threat?

Answer 3

surface water

Question 4

What can Nitrogenous compounds affect freshwater?

Answer 4

Make it unsuitable for drinking and harm in stream biota

Question 5

What is Ammonia (NH3)?

Answer 5

Unionised form, gas that readily dissolves in water, toxic to aquatic biota in very
small concentrations

Question 6

What is ammonium (NH4+)?

Answer 6

Ionised form, usually as a salt that readily dissolves in water and much less toxic
than ammonia

Question 7

What will Ammonia and Ammonium be like in aqueous solution?

Answer 7

exist in equilibrium

Question 8

How does pH affect the direction of ammonia and ammonium in aqueous solution?

Answer 8

low pH equation to to right = more ammonium (vice versa)

Question 9

What does TAN stand for? (ammonia-nitrogen practical)

Answer 9

Total ammonia nitrogen

Question 10

What is the aim of the ammonia nitrogen practical?

Answer 10

determine TAN concentration in 4 samples from the River Dud

Question 11

What are the four locations along the River Dud? (A B C D)

Answer 11

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

Question 12

Who produced the protocol for determining ammonia in water samples?

Answer 12

Keeney and Nelson 1982

Question 13

How is our method for determining ammonia different from Keeney and Nelson’s?

Answer 13

sodium salicylate for phenol

Question 14

what Equipment is needed for the Ammonia-nitrogen analysis?

Answer 14

• 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

Question 15

What reagents are needed for the ammonia nitrogen practical?

Answer 15

Sodium salicylate-sodium nitroprusside
Buffered hypochlorite
Ethylenediaminetetraacetic acid
Standard ammonium
Working standard

Question 16

How do you prepare a working standard for the ammonium nitrogen practical?

Answer 16

dilute 4mL of the concentrated solution to 200 mL in a volumetric flask with DIW

Question 17

What does DIW stand for?

Answer 17

di-ionised water

Question 18

What volumes of working standard need to be pipetted to prepare the standards?(mL) (ammonia-nitrogen practical)

Answer 18

0
1
2
3
5
10

Question 19

What dilutions need to occur to the working standard volumes to produces the standards? (ammonium-nitrogen)

Answer 19

25 mL to each flask

Question 20

What will the concentrations of standards be in the ammonium nitrogen dilutions? (ug of NH4+-N)

Answer 20

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

Question 21

What must you ensure to do with the beakers you have put the working standard dilutions in?

Answer 21

label the beakers 1-6 so the dilutions can be differentiated

Question 22

After the working stock dilution what is the next step of the ammonia nitrogen procedure? (EDTA)

Answer 22

Add 1ml EDTA to 25 ml volumetric flasks for the dilutions and water samples and swirl to mix

Question 23

After adding 1 ml EDTA to the dilutions and water samples what is added next? (ammonium nitrogen practical)

Answer 23

4 mL of salicylate-nitroprusside and then bring volume to 20ml with DIW

Question 24

How much of each water sample should you put into the volumetric flasks? (ammonium nitrogen)

Answer 24

3ml of each added to flasks labelled A-D

Question 25

Once the volume in the volumetric has been brought to 20ml what is added? (ammonia nitrogen practical)

Answer 25

2ml buffered hypochlorite and then immediately add DIW to take volume to 25ml

Question 26

What must be added first to the volumetric flask to ensure proper colour change? (ammonia nitrogen practical)

Answer 26

salicylate-sodium nitroprusside reagent must be added before the buffered hypochlorite reagent

Question 27

When the solutions of dilutions and water samples have been fully mixed in their individual flasks what do you do? (bath)(ammonia nitrogen practical)

Answer 27

transfer some of each solution into microcentrifuge, put in 37*c water bath for 30 mins

Question 28

Why are the microcentrifuges with the dilutions and water samples put in a dry bath? (ammonia nitrogen practical)

Answer 28

for colour development

Question 29

What do you do with the solutions after you take them out of the dry bath? (ammonia nitrogen practical)

Answer 29

Allow to cool
Put through spectrophotometer at 667nm (against DIW blank)

Question 30

What did Nelson 1983 say about the colour stability of samples in the ammonia nitrogen practical?

Answer 30

stable for 4 hours

Question 31

How long would it take for colour development of samples at room temp (23*c)? (ammonia nitrogen practical)

Answer 31

2 hours

Question 32

How do you get the NH4+ concentrations in the samples? (ammonia nitrogen practical)

Answer 32

obtain equation by linear regression of standard concentration and corresponding absorbance