NVWT_June_2012_JS.19.. - Napa Valley Wine Technical Group

Report
The Winery of Napa Valley
Michael Mondavi Family Estate
Jeanette Schandelmier
Topics to Cover
1. Which instruments were purchased for the
winery lab with a 1500 ton bond (250,000
gallons).
2. Focus on FSO2 using the Metrohm Titrino.
3. Touch on how much it costs to set up and how
much reagent expense is, as well as how long
the analysis takes.
4. Describe accuracy and precision, reliability and
durability of the Metrohm Titrino.
Mandatory Tools in a Winery Lab
 Autotitrator for F/TSO2 and TA/pH.
 Spectrophotometer for enzymatic analysis of Residual Sugar, Malic Acid,
Acetic Acid, NOPA and Ammonia
 pH meter (separate from autotitrator) for preparing buffers, acid trials, etc.
 Alcohol Analyzer (NIR)
 Turbidimeter (Hach)
 Oxygen meters (portable and benchtop)
 Pipettes for dispensing accurate volumes, stir plates, vortex
 Centrifuge, analytical balance, fume hood, water bath and stability oven and
refrigerator
 Microscope
 Ultrapure water for buffer preparation
 Vacuum pump for degassing wine samples
 Music source
FSO2 DETERMINATION BY
METROHM TITRINO
 We run at least 4500 FSO2 per year.
 We run pre- and post- FSO2 on each lot at monthly
topping, making sure we hit the target.
 Metrohm Titrino can also perform Total SO2 and TA
/pH (separate cartridge). The tests can not be run
concurrently.
 Manual dispensing of sample and reagents, no
turntable, though they are available.
 My prime directive is accurate results with a quick
turnaround time.
Metrohm Titrino
Both cartridges
FSO2 DETERMINATION BY
METROHM TITRINO
 How:
 The measurement utilizes titration of an acidified
sample containing iodine to an iodometric endpoint. A double Platinum sheet electrode that is
polarized by applying a current is used for
determining the endpoint. As long as the SO2 is in
excess, the voltage remains high and constant. As
soon as iodine is present in excess, the electrodes
depolarize and voltage drops toward 0 mV. (aka
magic)
Advantages of the Double Pt
Sheet Electrode
More appropriate for low level
measurements
–SO2(2 to 100 ppm)
50 times more surface area than double Pt pin
electrode allowing quicker response time.
Larger potential change at endpoint
–Improves accuracy and reproducibility
No reference or filling solution
Greater sensitivity than Redox

Free Sulfur by Metrohm Titrino
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Why: FSO2 is the amount of sulfur dioxide in wine that is functional as a preservative. It is important to make sure
the correct amount of FSO2 is present to ensure protection of the wine.
How: We use the Metrohm Titrino to analyze for FSO2. It utilizes titration of an acidified sample with iodine to an
iodometric end-point. The endpoint is measured with a platinum electrode.
Important Procedural Steps: Once you add the KI and the H2SO4, quickly place the beaker on the stir plate and
push start. Make sure you have a stir bar in the beaker and that it is not stirring too fast. Keep the platinum
electrode off to the side of the beaker so it does not get hit by the stir bar. Do not bend it and make sure the two
plates are not touching.
Safety: Safety glasses should be worn. The acid can burn you so use caution and if you get any on yourself, flush
with water immediately.
Procedure:
If the instrument is not already programmed for SO2, put module with Platinum electrode on titrator. Push “user
method”, “enter” and scroll using the arrow keys to SO2. Push “Enter”.
Using a 20 ml volumetric pipette, put 20 ml of sample into a 50 ml beaker along with a small stir bean.
Add 7 ml of 20% KI to the sample using the repipette.
Add 5 ml of 25%H2SO4 to the sample using the repipette and immediately place the beaker on the Titrino stir
plate.
Using extreme care, lower the electrode, temperature probe and dispensing tip down into the beaker by squeezing
the lever on the burette stand. Make sure the platinum electrode is near the side, away from the stir bean, so it
does not get hit.
Push “Start” to begin titrating with 0.0156 N Iodide-Iodate solution. Make sure the stir bean is mixing the solution.
If it does not stir, push the “stir” button on the main panel.
After the titration is complete, write down result, rinse probe, dispensing tip and temperature probe and leave in
air.
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Reagents:
1. Use premade and purchased Iodide-Iodate solution and 25% H2SO4.
2. 20%KI: Weigh out 100 grams of KI using the analytical balance and put into a 500 ml graduated cylinder. QS to
500 ml using ultra pure water. Mix well.
0
6S 6SB
B
0
0
6S 0 1 3A
A
B
0
6C 0 1 N
S5 A O SA
0
8
6C PQ TV
N
S
5 1
0
6C 9PQ O T
VN
S
2
0 56V O
6C
Q T
S5 1 VN
O
7
0
6C V Q TV
N
2
S
0 58P O T
6C Q
V
N
S5 1
9P N T
0
Q
V
5C 2
N
S2 N V
0
0
5C Y TN
S2 N T
7Y V
N
N
TV
0
5
N
0 CS2
5C
4B
S8
5 V
0
0 HV
5C 6C
Y
S1 S
LE
2
A
E
0
5C O S
T
S
V
0
N
5C 1 3
O
S3
T
V
7
0
5C Y O N
S3 T
VN
0
5C 8Y
S3 O T
0
6C 9Y VN
S1 O T
4 Y VN
N
0
5C TV
SL N
EE
S
0
5C C L
S7
5A
0
0 5 CS
5C 7
S 5B
0 90
5C ZR
S9 2
0
ZR
0
2
0 5 CS
5C
78
S9
B
0
ZR
2
0
Lev el o f FSO 2
Io do met ric v s. M ea n o f PI/ AO/ ETS
35
30
25
20
I/ I
M ea n
15
10
5
0
I/ I v s. M ea n
Accuracy:
+/- 2 ppm for FSO2 and +/- 5 ppm for TSO2
+/- 0.2 g/L TA and +/-0.02 pH
The mean of my control is based on accumulation of data (at least 30 initial
data points, plus data from the reference lab) and I use 2 standard
deviations from the mean as acceptable. I use quality control charts so I can
quickly see if I am outside 2 SD or have a trend or shift developing.
Precision or reproducibility:
+/- 1 ppm for FSO2 and +/- 4ppm for TSO2
+/- 0.2 g/L TA and +/-0.02 pH
REFERENCE LAB
MMFE
FSO2 (ppm)
32
31
TSO2 (ppm)
74
75
TA (g/L)
5.8
5.71
pH
3.54
3.55
Out of control can be outside 2 std dev, 7 consecutive points in an
upward or downward trend or 7 consecutive points above or
below the mean.
TA/pH
TA 6.0 g/L Tartaric Acid High/// pH Control Supersaturated KHT 3.57
TA
1
2
3
4
5
6
7
8
9 #
#
#
#
#
#
#
#
#
#
#
#
#
#
#
x
6.2
x
x
6.1
x
x
6.0 g/L
x
x
x
x
x
x
x
x
x
x
x
x
5.9
x
x
5.8
x
#
#
#
#
#
#
Time and Money
 Each sample takes 3 to 4.5 minutes including
pipetting and clean up (I use bottletop dispensers).
 In 2007 I paid $7,500.00 for the instrument with SO2
and TA/pH cartridges and Pt electrode. The
turntable would have doubled that price.
Replacement Pt electrodes run $310.00. pH probes
run $540.00.
 Reagents include 20% KI ($77/500 g = ~350 tests),
25% H2SO4 ($27/L= 200 tests) and 0.156 N IodideIodate ($22/L = ~200 tests) solution. So reagents run
47 cents per test to run a FSO2.
Since building the lab in
2007…
 There are over 65,000 results in WMDB.
 We have served 39 different clients.
 We’ve tracked ~750 lots from grape to bottle.
 We’ve gone through 3 Platinum electrodes and 5 pH
electrodes.
 Annual maintenance recommended on Titrino and
NIR.
Questions?
 [email protected][email protected]

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