american society of enology and viticulture milrod presentation
TRANSCRIPT
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
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.
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
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
SO2 Titration Curve
SO2 = 28.04 ppm
Comparison of Free SO2E.T.S. vs A/O vs Bivoltametry
06CS58
PQ1 OTVN
06CS59
PQ2 OTVN
06CS56
VQ1 OTVN
06CS57
VQ2 OTVN
06CS58
PQ1 NTVN
06CS59
PQ2 NVTN
05CS20
Y NTVN
05CS27
Y NTVN
05CS24
BV
05CS85
HVY
06CS LE
ES
05CS12
A OTVN
05CS13
OTVN
05CS37
Y OTVN
05CS38
Y OTVN
05CS39
Y OTVN
06CS14
Y NTVN
05CSLE
ESCL
05CS75
A
05CS75
B
05CS90
ZR2
05CS90
ZR2
05CS78
B
05CS90
ZR20
5
10
15
20
25
30
35FSO2 Comparison
A/OETSPIMean
Blend ID by Grouped Comparison
Leve
l of F
ree
SO2
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
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
Vial vs Beaker in Automation• SO2 is volatile• Titration using a
traditional beaker is inappropriate in automation
vs
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
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
Widest range available
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
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
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