Chromatography Forum

Greetings:

I need a method for estimating inositol in a nutraceutical formulation. The problem is, I do not have an RI detector or an ECD. I have to use a UV or PDA only.

Any ideas, people? Can I derivatise inositol using benzoyl chloride, or can I use an ion-pair reagent? Any ideas are welcome. Running out of time!

Thanks in advance.

SK Srinivas
analysciences@gmail.com

There's no chromophore in inositol, so ELSD would be my first choice for detectors. Unfortunately without derivatisation PDA/UV will not work

If you do not want to use Amino columns, you can try HILIC columns, or the Amide columns (BEH/XBridge) from Waters.

You could use indirect UV-detection. Not sure if it will be sensitive enough -you'll have to try.
Maybe this article gives some ideas: http://www.ncbi.nlm.nih.gov/pubmed/11355833

Thanks for your help, rwang and Thomas! I'll try the ion-pair method and keep you posted.

SK Srinivas

I don't think you can pair an ion to sugar. You could go to very high pH and do ion exchange. Or better, use a Biorad 87H or equivalent (Hydrogen form ion exclusion). Myo inositol is 'retained' a nice amount. Throw in your indirect UV detection and you may have a method.

As mardexis indicated, you can't do ion-pair unless you have an ion. I'm not sure that inositol ionizes, even at high pH. All the references to ion exchange that I've looked at deal with phosphorylated inositol.

The "ion exclusion" columns actually work more by partition chromatography for sugar alcohols. Because the inositol will elute in addition to the mobile phase components (as opposed to "instead of"), indirect UV probably will not work (indirect UV involves replacement of a UV absorbing species with by a UV transparent species).

Derivatization with DNBCl is probably your best bet, but by the time you get the derivatization reaction to run, get a unique product, get rid of the excess reagent, and figure out the separation conditions, it may be more cost-effective to buy an appropriate detector.

Tom is probably one of the worlds top experts on ion exclusion chromatography but if you try this separation I would suggest you try the indirect anyway. I did find a reference using the Biorad 87H:

Non-suppressed conductivity and indirect UV detection of carboxylic acids in environmental samples by ion-exclusion chromatography using 2,6-pyridinedicarboxylic acidic eluent
Journal of Chromatography A
Volume 859, Issue 2, 29 October 1999, Pages 173-181

Buying an RI detector though seems like the right thing to do. You could probably get a used one super cheap!

the myo-inositol comes out at 9.42 minutes with 0.005 M sulfuric; 50C; 0.6 mL/min; 300x7.8mm biorad column