Google is your friend. The compound is Na2SeSO3. My guess would be that it's fairly easy to oxidize to selenate and sulfate. I found this reference near the top of the search page ('selenosulfate'): http://pubs.acs.org/doi/abs/10.1021/es202529w
Identification and Determination of Selenosulfate and Selenocyanate in Flue Gas Desulfurization Waters
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From: Louis Wagner <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, March 23, 2017 3:26 PM
Subject: Selenosulfate analysis (Selenium Speciation)
I'm wondering if anyone has any experience with Selenium speciation (By HPLC-ICPMS or similar) in particular separating and quantifying Selenosulfate (SeSO4)? I'm looking for some advice on getting the chromatography to work.
I am using a Sodium Selenosulfate solution purchased from Sigma Aldrich (778354-25ML). This happens to be a mixture of Sodium Selenosulfate, Sodium sulfate and water. When I inject this on the system I get a Selenium peak that has a nearly identical retention time to Se4 yet no corresponding Sulfur peak at this retention time. There is a sulfur peak in the chromatogram but no corresponding selenium peak at that retention time. You see my problem? It looks like I'm seeing peaks for sulfate and Se4 but but nothing that might indicate selenosulfate which should have both a selenium peak and sulfur peak at the same retention times. It's as if Selenosulfate itself is not stable in my chromatographic conditions.
This is on a Agilent 7700 coupled to an Agilent bioinert LC. Column is anion exchange.
National Technical Specialist-Inorganics, Environmental