SC-100A manual
11
Version 3.1c
How can I check the accuracy of my reagents?
It’s rare that the SO
2
reagents go bad, but if you are concerned about it you can run the 'Ascor-
bic Acid Test' method located in the FAQ section of the website to check your SO
2
reagents.
https://vinmetrica.com/wp-content/uploads/2012/04/Ascorbate_stdization_procedure-500-mg.pdf
I added the calculated amount of sulfite to my wine but the numbers are still low!
This is a common occurrence with several explanations, any or all of which may be happening.
1.
Make sure you are using fresh sulfite powder. Potassium metabisulfite degrades over time and
that stuff you bought 2 years ago is probably bad now!
2.
Make sure that you stir your wine thoroughly when you add sulfite. If you pour a 10% solution
of KMBS into your wine, it sinks like a battleship!
3.
A significant portion of the sulfite you added may have ended up ‘bound’, particularly if your
free SO
2
was very low to begin with. This bound SO
2
does not show up when you measure free SO
2
,
and it is not protecting your wine. You will need to add more sulfite until your free SO
2
comes up to
the right level. Sometimes you must add two or even three times more sulfite than you first calculated.
I’m getting strange results in SO
2
mode; how do I know if my instrument is
working correctly?
For SO
2
measurements with the SC-100A, there are several quick tests you can do to make sure
the instrument is not faulty.
1. Be sure the battery is good per the manual’s instructions.
2. Connect the electrode and put it in about 20 mL of distilled water; add about 1 ml (half a bulb
squeeze) of each of the SO
2
Acid Solution and the SO
2
Reactant Solution and swirl in the usual
way, keeping constant motion. The instrument may or may not indicate STOP as above. If it does
not, add a drop of the SO
2
Titrant solution. This should make the STOP condition occur, with a cur-
rent of 100-300 nA. [If it doesn't you may have an electrode problem; read in the next section be-
low how to fix this.] Now add one drop of a concentrated sulfite solution (1-10% is fine) and verify
that the STOP signal ends and the PROCEED light illuminates. If this test passes, your system is
detecting the titration endpoint correctly.
3.
The platinum wires of your SO
2
electrode could be dirty (crust, debris, etc.) even though you may
not be able to see anything. First, soak the SO
2
electrode in your Acid Solution for about 10
minutes and rinse with DI water. Using the back edge of a pocket knife or something similar, very
gently scrape the two platinum wires, being sure not to bend or break them. Thoroughly rinse with
DI water and try your test again.
