AFIA - Laboratory Methods Manual - Australian Fodder Industry ...

Working solutions:
1. NaOH - 40% (Alkali):
(a) Decant 1 ± 0.01 L water in plastic container
(b) Gradually add 4 ± 0.01 L of 50% sodium hydroxide while stirring. This solution gets hot.
Container may be placed in cold water to help cool.
(c) Transfer into Kjeltec Alkali reservoir.
or,
(a) prepare 40% solution by adding 400 ± 1g NaOH pellets or flake, CAREFULLY into
900mL of water, and making up to a litre.
2. 1% Bromocresol green solution:
(a) Add 0.25 ± 0.005g Bromocresol Green in 250 mL methanol, and stir till dissolved.
3. 1% Methyl red solution:
(a) Add 0.25 ± 0.005g Methyl Red in 250 mL methanol, and stir till dissolved
4. Receiver Solution:
(a) Dissolve 50.0 ±0.1g of boric acid and made up to 5 L with water.
(b) Add 50 ± 1 mL 1% Bromocresol green solution and add 35 ± 1 mL 1% Methyl red
solution. Mix thoroughly.
(c) Gradually add NaOH until the solution is between a red and green colour (grey/green)
and add to container beneath Kjeltec Analyser.
5. HCl Standard acid solution - 0.1M HCl:
(a) Add 20.0 ± 0.1 mL of 32% (10M HCl) to approx 1200 mL of water and make to 2 L
volume with water.
(b) Depending on the sample size and ammonia N content, standard acid solutions with
concentrations ranging from 0.02 to 0.1 M may be used for titration of the receiver flask
solution.
(c) The standard acid solution can be prepared from ampoules of various concentrations or
by diluting concentrated hydrochloric acid (36%, 12 M ) with water.
6. Mixed Indicator solution:
Procedure:
(a) Use equal volumes of solutions 1% Bromocresol green and 1% Methyl red solutions.
Silage extract
1. Weigh 50 g of chopped silage (for chopping procedure see Silage pH Method 1.12R) into an
open neck glass bottle with a screw cap.
2. Cover with 250-450 ml 0.3M sulphuric acid and replace the cap. Stir gently. The higher volume
will be required for drier silages.
3. Record the volume of acid used as it will be required when calculating the result. Do not add
excessive acid as this will dilute the concentration of ammonia-N in the filtrate.
AFIA Laboratory Methods Manual – v7 September 2011 Page 28 of 103