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Chemical Stability and Compatibility - Stability of iodide (I) in acid matrices

 
We recently received a request for an I (iodide) standard in 10% HCl. We understood I is not stable in acid, but is this the same for any I concentration in any acid concentration? Would it be possible to purchase your stock CGICI1-1 (1000 µg/mL iodide) but spike it at 10 µg/mL in a 10 % HCl multi element working stock and make a calibration sequence from that working stock? Will this give instability problems for the I?
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The issues with iodide instability are due to pH (or more precisely Eh), as below a pH of about 5 it’s possible to oxidize iodide to iodine, which is not only volatile, but non-polar so it’s notorious for sticking to plastic. To prevent this from happening the solution needs to remain reducing, which is not straightforward if exposed to air. Diluting iodide in 10% HCl might be suitable for immediate measurements, but we have not studied this in detail and can offer no information regarding the stability of such a preparation.

Posted: 08/31/18 00:03:40

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