[ChrisMasterjohn]

Hi everyone,

I have a question.  I have been having a problem with ascorbic acid standard curves when using plastic in the preparation process.  In serial dilutions of uric and ascorbic acids, uric acid always comes out perfect but ascorbic acid from the same dilution has certain points that are extremely elevated.  Measurements of ascorbate from control plasma come out consistent.  I seem to have solved the problem by preparing in glass and injecting from glass HPLC vials rather than preparing in plastic conical and microcentrifuge tubes while injecting from polypropylene vials.  However, we have always used plastic in the past with no problems.

I'm wondering if degradation products from our ascorbic acid standard could be reacting with our plastic.  Can anyone thing of a reasonable explanation?

Thanks,
Chris

[marquis]

Best guess would be an antioxidant. There are a number of antioxidants often present in polypropylene.  Generally, it is assumed that they won't extract out.  This is not always the case.  One common antioxidant I ran across is BHT (butylated hydroxytoluene).  There are many others. 

There are many other ingredients in polypropylene.  These can be polymerization catalysts, inhibitors, lubricants, etc.  Any of these is also possible, although the antioxidant is more likely.

The problem will be getting the plastic manufacturer to tell you about the materials they use.  It's proprietary information that is rarely disclosed.