Measuring Total SO2 with Vinmetrica SC-100

[ybl84f1]

After a couple of weeks of aging I measured the Free SO2 in my (kit) wine with the Vinmetrica SC-100 and I got a reading of 38 ppm which seemed like a reasonable value to me, especially since the kit came with it's own sulphite+sorbate package and it seems from my reading that 35-50ppm is a typical target level.

The directions for the SC-100 go on to say that you can also measure Total SO2 with just 2 changes - 1) using 8 mL of Acid Reagent (instead of 2 mL) and 2) using 1N sodium hydroxide, which is a different normality from the sodium hydroxide that is supplied with the SC-100 to measure Free SO2 which has a normality of 0.0156N. The Normality is a measure of concentration.

When I attempted to measure the Total SO2 using 1N sodium hydroxide (and 8 mL Acid Reagent) the red stop LED immediately lit up without any titration, indicating the Total SO2 was less than 2 ppm! This doesn't seem right. My understanding is that Total SO2 = Free SO2 + "bound-up" SO2 and therefore should be greater than or at least equal to at least my Free SO2.

Dos anyone use the Vinmetrica to measure Total SO2? Any thoughts?

 

[Rice_Guy]

I have not worried about total yet.
The lab bench version uses a peroxide to convert bound back into free SO2 therefore have guessed that either reagent A or B was peroxide, I did not assume Vinmetrica A stands for acid reagent and B was peroxide. As far as the meter/ red, it is measuring nanoamps, ,, a few times it seems to be instantly red which mixes out.

Vinmetrica tech support should have seen this, if you ask post back so we can all learn.

 

[mainshipfred]

I've always found Vinmetrica tech support to be very helpful and friendly.

 

[ybl84f1]

Just a quick update - I have not heard back from Vinmetrica either directly from their email support or via this forum. I've reached out to them again and will post any responses.