Hach-Lange DR 5000 brewerie analysis, supplementary software LZV570 - Manual (Page 33)

33
Working procedures
• Iodine solution, 0.02N (prepare freshly each day from the stock
solution)
• Phosphate buffer solution, 0.1M, pH 3.5: adjust the pH of a
0.1M KH
2
PO
4
solution to 3.5 with 0.1M phosphoric acid
Sample preparation
1. Pipette 10.0 ml centrifuged wort, or carbon-dioxide-free beer,
into a centrifuge tube.
2. Add 40.0 ml ethanol and shake mechanically for 10 min.
3. Centrifuge for 5 min at 2500 rpm.
4. Carefully decant as much of the clear phase as possible.
5. Dissolve residue in 20.0 ml phosphate buffer solution by
shaking mechanically for 10 min.
6. Centrifuge the solution for 5 min at 2500 rpm.
7. Pipette 2 ml of the supernatant liquid and 8 ml phosphate
buffer solution into a 40 mm rectangular cuvette and measure
at 578 nm against phosphate buffer solution.
8. Add 0.5 ml 0.02N iodine solution, mix the contents immediately
with the plastic spatula, then measure after 30 sec.
9. Iodine blank solution
a. Pipette 10 ml phosphate buffer solution and 0.5 ml 0.02N
iodine solution into a 40 mm rectangular cuvette and mix.
b. Measure absorbance at 578 nm against phosphate buffer
solution.
Results
The results are expressed as absorbance to 2 decimal places.
Accuracy
Vcr = ± 3%
Standard values
< 0.3 (wort)
Literature
MEBAK Brautechnische Analysenmethoden
4th Edition 2002 Volume II, pp 34ff