6
PRINCIPLE OF OPERATION
Determination of sulphur dioxide in wine samples is made by titration of the sulphur dioxide present
in wine with iodate. In this procedure an excess of iodine is added to the wine sample and it is
titrated with iodate.
The iodate reacts with iodide and the sulphuric acid present in the wine and produces iodine:
IO
3
- + 5I- + 6H
+
= 3I
2
+ 3H
2
O
The iodine produced in the reaction above reacts then with the sulphur dioxide:
H
2
SO
3
+ I
2
+ H
2
O = H
2
SO
4
+ 2HI
For precise results it is very important to know the exact sample volume, titrant volume and
concentration.
The peristaltic pump has a good repeatability but the dosing volume depends on many factors as the
diameter of the tube or the tube stretching. To compensate for all this errors, the pump need to be
calibrated. The calibration of the pump is also needed in order to have high precision of the titrations.
The calibration procedure is in fact the analysis of a known solution. By doing this, the instrument
makes a differential analysis between the standard and the wine sample. The pump volumetric debit
and the real concentration of the titrant is compensated. Only the sample volume has to be precisely
known.
15
PUMP CALIBRATION PROCEDURE
Warning:
The calibration of the pump must be performed each time the pump tube, the reagent
bottle or the pH electrode is changed. It is recommended to perform the pump calibration before each
set of measurements.
• To prepare the sample for calibration, follow the
measurement procedure for Free or Total SO
2
measurements by using
HI 84100-55
Standard
instead of wine sample.
• After sample preparation, press the CAL PUMP button.
Std will blink on the screen.
• Press START STOP in order to start the system
calibration.
• At the end of the calibration procedure done appears
for a few seconds and then the meter automatically
returns to measurement mode.
PUMP TUBE REPLACEMENT
To remove the tube of the peristaltic pump follow next steps:
• Detach the old tube system from the reagent bottle.
• Grasp one fixing ring of the peristaltic pump tube.
• Pull the tube until it’s taken out from its location.
• Remove the other side of the tube.
To mount the new peristaltic pump tube follow next steps:
• Position one peristaltic pump fixing ring on its location.
• Stretch the tube over the peristaltic pump cylinders.
• Fix the second pump fixing ring on its location.
• Attach the tube to the reagent bottle.
Note:
Purge the peristaltic pump until drops of reagent appears on the dosing tip by pressing the
PURGE button.