- SO2 is an important compound present in both free and bound forms in wine that is often measured through titration. Metrohm offers automated wine analysis systems that can precisely and accurately measure levels of SO2, pH, acidity, and other parameters. Their Dosino technology and pre-standardized reagents help improve the productivity, accuracy, and safety of wine analysis. Metrohm has a long history of developing innovative electrode and titration technologies for ion analysis.

1. Wine Analysis:
SO2 Determinations
and more…
Arthur Milrod
Metrohm USA
415-286-3665
amilrod@metrohmusa.com
www.metrohmusa.com

2. Agenda
• The Chemistry of SO2 in Wine
• Advantages of the Double Platinum Sheet Electrode
• SO2 Titration Curve
• Unique Technology in Wine Automation
• The Importance of Automation
• Advantages of Metrohm Dosino® Technology
• Unique pH electrodes

3. A Bit of Metrohm History
• For 65 years and unique in the industry, ion
analysis is all we do.
• First combination electrode in 1950.
• First piston driven buret in 1956.
• First digital titrator in 1968.
• Still hand-makes electrodes.

4. The Chemistry of SO2 in Wine
• Sulfite or sulfurous acid (SO2) is present in wines and musts in free and
bound form.
– Bound SO2 represents the main fraction of the Total SO2.
– Sulfite is oxidized to sulfate (sulfuric acid) by iodine.
• A double Pt-sheet electrode that is polarized by applying a current (e.g. 1
μA) is used for determining the endpoint.
– Known as bivoltammetry (two electrodes polarized by applying a current, the
voltage is measured).
– As long as an SO2 excess is present, the resulting voltage remains relatively
high and approximately constant (about 300 mV).
– As soon as iodine is present in excess the electrodes become depolarized and
the voltage drops toward 0 mV (L-shaped titration curve).
• SO2 + H2O = H2SO3 (sulfurous acid)
• H2SO3 + I2 + H2O = H2SO4 (sulfuric acid) + 2 HI
• Iodide-Iodate (KI-KIO3) vs I2

5. Advantages of the Double Pt Sheet
Electrode
• More appropriate for low level
measurements
– SO2 (2 to 100 ppm)
– Residual Chlorine (ppb)
• 50 times more surface area than double Pt
pin electrode
• Quicker response time
• Larger potential change at endpoint
– Improves accuracy and reproducibility
• No reference or filling solution
• Greater sensitivity than Redox

6. SO2 Titration Curve
SO2 = 28.04 ppm

7. Comparison of Free SO2
E.T.S. vs A/O vs Bivoltametry
0
5
10
15
20
25
30
35
LevelofFreeSO2
Blend ID by Grouped Comparison
FSO2 Comparison
A/O
ETS
PI
Mean

8. Unique Technology in Wine Analysis
Automation
• SO2 is Volatile
– Traditional in-beaker titrations is not optimal
– Automated pipetting technique with external
vessel increases accuracy
• Degassing for TA in wine
– Needle to purge solutions of interfering gases
– Flexible purge times

9. Advantages of Metrohm Dosino® Technology
• Highly accurate dosing device
• Top-to-bottom piston design
– Keeps air bubbles at the top of the buret and away
from reagent lines so not to affect results
• The Smart Chip™ memorizes reagent information
such as:
– Concentration
– Standardization value
– History
• Checks for the correct titrant
– Including its working life and need for
standardization
• The electronic motor is mounted on the top
– No damage by a reagent leak

10. Vial vs Beaker in Automation
• SO2 is volatile
• Titration using a
traditional
beaker is
inappropriate in
automation
vs

11. The Importance of Automation…
• Productivity:
– Frees up users time to focus on other projects
• Accuracy and Precision:
– Automation will run samples in a consistent manner for better accuracy and
precision
• Safety/Exposure Limitations:
– Leaving an automated system unattended will keep user safe from constant
exposure to potentially harmful chemicals

12. Automated Analysis of Wine
• Completely automates the
determination of wine
• Analyses include:
– pH, Total Acidity, SO2, NH3,
K+, reagent standardization
– Customized systems
available for additional
analyses
• Pipetting
– Pipettes sample volumes
from 10mL to 25mL
• Built-in electrode input with
temperature compensation
– Saves bench space
– Improves accuracy

13. Widest range
available

14. Unique pH Electrodes
• Fixed ground sleeve diaphragm
– Ensures optimal and well
defined electrolyte outflow
– Eliminates back-diffusion of
sample into the reference
electrolyte
– Contamination of the reference
system is prevented
• Cylindrical pH glass membrane
– Increased surface area ensures
fast response for quick and
stable readings

15. Quality & Reliability
• Off the shelf systems
– Available in stock
• 10-Year availability of parts
• 3 Year parts and labor
instrument warranty
• Local, on site service and
support
Metrohm USA Warehouse

16. Our Pre-standardized Certified Reagents help:
• Save time, as the normality on the label can be
entered directly into the system.
• Reduce technician’s need of handling reagents, as
they can attach directly to the buret.
• Certified against N.I.S.T. primary standards using
Metrohm instrumentation, with the Certificate of
Analysis right on each bottle.
Reagents are an often overlooked
cause of inaccuracy in titrations