Incompatible Substances

[syx]

Dear all,
How do we prepare sample solution for determining a substance that could be degraded in the present of other substances in product, in the solution? For example, vit B12 in a USP dietary supplement product that also contains vit C, Cu, and Fe...
Thanks in advance.

Regards,
Siswanto

[tom jupille]

Assuming that you are not interested in quantitating those other substances, you prepare a diluant that contains additives which will react/complex with them faster/more than will your analyte.

As an example, many years ago, I ran assays for sulfite in foods. Sulfite is rapidly oxidized to sulfate, so the extraction buffer contained ascorbic acid. so, if you want to keep ascorbate and metals out of the way, maybe a reducing agent plus something like EDTA would work

[krickos]

Hi

Yes, as Tom said introducing an antioxidant may be a way around it. Some pharmaceutical injection solutions for instance contain excipiants API and adrenaline, adrenaline is also sensitive for oxidation with for traces of example Fe/Cu so products may contain low amounts of metabisulphite. So if your samples/standards are prone to oxidation/degrradation it is not a bad idea to add an antioxidant.

The tricky part is to find a suiteble one that wont interfere with analysis and try out a suiteble concentration (will likely take some time to monitor short term stability).

Sometimes simple temperature might be enough ie use cold (2-8°C) disolution solvents and temperature controlled vial compartment.

[HW Mueller]

If B12 is easily oxidized why would ascorbic acid increase this tendency? I would add more ascorbic acid which could obliterate the catalytic action of the metal ions. Or just forget about the ascorbic and remove the metal ions as mentioned above.

[syx]

does anyone have experience with metamizole (methampyrone) and vit Bs? this substance is hydrolyzed rapidly in the present of water, so we need to use non-aqueous solvent. in the solution that contains vit B1 it will be degraded too (the sample is tablet that contains metamizole and vitamin B complex). what should we add to the solvent to avoid this reaction?