Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 22)

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Working procedures
2.6 Free amino nitrogen (ninhydrin method based on EBC method)
Principle
The test solution is heated with ninhydrin at pH 6.7 and the
resulting colour is measured at 570 nm. The method covers amino
acids, ammonia and also the terminal alpha-amino groups of
peptides and proteins. Proline is partially detected at the
wavelength used. The method is not specific for
alpha-amino-nitrogen, because gamma-amino butyric acid, which
occurs in worts, also reacts with ninhydrin to produce a colour.
Fields of application
Beer, worts
Measuring range
0–400 mg/l
Accessories
• Test tubes with ground-glass stoppers (16 x 150 mm)
• Variable pipette (1.0–5.0 ml) (BBP 065)
• Pipette tips for pipette (BBP 068)
• Water bath suitable for boiling water
• Water bath (20 °C)
• Spectrophotometer (570 nm)
• 10 mm rectangular cuvette (OS grade)
Reagents
• Colour reagent: Dissolve 10.0 g disodium hydrogen
phosphate (Na
2
HPO
4
x 12 H
2
O), 6.0 g potassium dihydrogen
phosphate (KH
2
PO
4
), 0.5 g ninhydrin and 0.3 g fructose in H
2
O
and make up to 100 ml. This solution remains stable for 2
weeks in a dark bottle. The pH must be 6.6–6.8.
• Dilution solution: Dissolve 2 g potassium iodate in 600 ml
H
2
O and add 400 ml 96% ethanol
• Stock solution: Dissolve 107.2 mg glycine in 100 ml H
2
O.
Keep this stock solution at 0 °C.
• Standard solution: Make up 1 ml stock solution to 100 ml with
H
2
O. This standard solution contains 2 mg/l amino-nitrogen.
Sample preparation
1. Dilute wort 100-fold, beer 50-fold (1–3 mg/l amino-nitrogen)
2. Analyse sample, standard solution and blank value solution
three times.
3. Pipette 2 ml of the diluted sample or the standard solution or
H
2
O into a test tube.
4. Add 1 ml colour reagent and mix.