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SO2 testing with indicator solution.

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kuziwk

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I'm testing with the standard indicator solution, however instead of using 25% phosphoric acid I'm using 2% w/v sulfumic acid crystals in tap water. At any rate when I run my test for 15 minutes with the pump on, the sulphite levels are lower than expected. Once I titrate the indicator solution back to neutral from magenta, I run the test further with what's left of the wine sample and leave it for another 15 minutes and its still turning the indicator solution magenta. It seems that all the SO2 is not liberated in fifteen minutes. Can I just run the test longer, maybe for 1/2 hour? Or will this somehow make the test inaccurate.
 

RPh_guy

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The main reason that a longer test may lead to inaccuracy is because bound sulfite will release over time as it tries to reach equilibrium.

Whether this is the effect you're seeing or whether the pH isn't being dropped low enough with sulfamic acid sort of depends on what you mean by "lower than expected". There are a variety of reasons why sulfite could actually be lower than expected.

Also be aware the air should be running between 1.0-1.5L/min.
 
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