Hach-Lange LZV936 - DR 6000 Brewery Analysis software - Handbuch (Seite 44)

English 44
Reagents
Prepare all solutions with iron-free dist. H
2
O.
• Buffer solution, pH 4.3: dissolve
75 g ammonium acetate and 150 g concentrated acetic acid in
approx. 800 mL dist. H
2
O, check pH and top up to 1 L.
• Ferrozine reagent: dissolve
0.257 g ferrozine or ferrospectral in 50 mL buffer (solution can be
stored for 2 weeks)
• Ascorbic acid, 2.5 % (prepare fresh daily)
• Hydrochloric acid, concentrated
• Iron(III) standard solution for determination of the calibration curve:
dissolve 863.4 mg ammonium iron(III) sulfate [NH
4
Fe(SO
4
)
2
x 12
H
2
O] in the 1 L volumetric flask in dist. H
2
O and after addition of
0.1 mL concentrated hydraulic acid top up with dist. H
2
O to the
mark. After dilution of 50 mL of this solution with dist. H
2
O to 1 L,
the resulting standard solution contains 5 mg/mL Fe 3+ .
Sample preparation
1. Remove the carbon dioxide in the beer and allow the foam to
subside completely.
2. Pipette 40 mL beer, 2 mL ferrozine reagent, and 1 mL ascorbic
acid solution into a 50 mL volumetric flask.
3. Fill to the mark with dist. H
2
O.
4. Prepare the blank value without addition of ferrozine reagent. Use a
separate blank for each individual beer.
5. Measure the extinction of the solution in a 40 mm rectangular
cuvette at 560 nm against a corresponding blank value.
Results specifications
In mg/L with three significant places
Accuracy
r = 0.0080
Target value
< 0.200 mg/L
Literature
MEBAK brew-technical analysis methods, 4th edition 2002
Volume II, P. 149 et seq
Procedure for iron
1. Prepare the blank values and samples according to the work
procedure.
2. Select STORED PROGRAMS > SELECT BY NUMBER.
3. Enter the number 2017 for the program "Iron". 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.