Hach-Lange LZV936 - DR 6000 Brewery Analysis software - Handbuch (Seite 43)

English 43
7. Main value
• Add 0.5 mL 1,2-phenylenediamine solution, mix and place in
the dark for 30 min.
• Add 2 mL 4N hydrochloric acid.
8. Measure the extinction of the main value against the blank value
within 20 min at 335 nm in a 20 mm rectangular cuvette.
Results specifications
In mg/kg with two decimals
Accuracy
s = ± 0.01
Target value
For light full beer <0.15 mg/kg
Comments
The distillation appliance does not need to be cleaned or purged
between individual tests and can be immediately refilled between tests.
After testing is complete, the adherent residues should be removed with
dilute sodium hydroxide or another suitable cleaning agent.
Acetohydroxy acids present in bottled beer are oxidized in the presence
of oxygen to diketones. The beer sample can, for analysis of the total
diketone content before the actual analysis, be maintained for 1.5 h at
70 °C (158 °F).
Literature
MEBAK brew-technical analysis methods, 4th edition 2002
Volume II, P. 134 et seq
Procedure for vicinal diketones
1. Prepare the blank value and the samples according to the work
procedure.
2. Select STORED PROGRAMS > SELECT BY NUMBER.
3. Enter the number 2014 for the program "Vicinal diketones". Confirm
with OK.
4. Press START to start the program.
5. Enter the blank value (see sample preparation) and press ZERO.
6. Insert the analysis cuvette with the prepared main value and press
READ.
The result is shown on the display.
Note: To analyze further samples, repeat the procedure from step
5.
Iron
Iron can dissolve into beer through raw materials, filter additives, and
clarifiers. It can also be absorbed from appliances, lines, containers,
and beer foam stabilizing agents. Iron negatively effects the colloidal
stability, the taste and the gushing tendency of the beer.
Principle
Bivalent iron forms a violet colored complex with a very high molar
extinction coefficient with the di-sodium salt of 5,6-diphenyl-3-(2-pyridyl)-
1,2,4-triazine-4,4-disulfonic acids (ferrozine). Trivalent iron must be
reduced to bivalent ion iron before measurement. The color intensity is
measured spectrometrically.
Measurement range
0–1 mg/L
Accessories
• Weighing balances, reading precision 0.1 mg
• Pipettes, 0.1 mL, 2 mL, 5 mL
• Spectrophotometer, 560 nm
• 40 mm rectangular cuvette OS