Tannates

[Jay-Z]

I am currently working to develop an HPLC method to quantitate the active ingredients in a pharmaceutical product containing tannates...in particular phenylephrine tannate is proving most difficult.

This method has proved problematic because the tannic acids produce *many* interfering peaks that junk up the chromatagram, and since phenylephrine is fast eluting, these seems to be little wiggle room.

I've tried a million different conditions, differnent columns, mobile phases, with and without ion-pairing, etc.

Has anyone had success with this (or similar compounds)?

Would a Dionex OnGuard II P sample prep cartridges be useful? Or some other sample prep product?)

Any suggestions would be greatly appreciated!

jay-z

[SIELC_Tech]

Check these two links. One describes the retention of phenylephrine on a Primesep C column. The mobile phase (ACN-water-ammonium acetate) and depending on the pH of the mobile phase you can retain this basic compound from 6 minutes up to 30 minutes on the column. But 30 minutes might not be necessary because tannic acid will behave differently. Primesep C column retains compound by reverse phase and cation exchange mechanism (pH=3-7), so your acid would only be retained by hydrophobic mechanism and I don’t think that tannic acid will retain as strong as your target compound.

http://allsep.com/makeCmp.php?cmp=Cmp_166


Also check the following newsletter. You can see how to use the guard column to trap compounds you do not want to see or analyze. If you put Primesep B2 or Primesep D guard it will probably trap your tannic acid. These guards will not retain phenylephrine but rather help you to trap (or slow down) compounds which are acidic in nature. You have enough room between void and phenylephrine to “pass a trainâ€

[Jay-Z]

We are using a UV detector.

[Uwe Neue]

Sample preparation with a strong ion exchanger might be the best tool. There are two options, depending on your sample.

As the first choice, I would use an anion-exchanger such as an Oasis MAX cartridge at alkaline pH to retain the tannins, and wash all analytes out at high pH and methanol. If all your analytes are as polar as phenylephine or more polar, you may not need to go to 90% or so methanol, but elute with a solvent mix containing less organic.

If all your analytes are bases, you may be able to this with a standard cation exchange protocol on an Oasis MCX cartridge. load the sample onto the cartridge at acidic pH, then wash with acidified methanol, and then elute methanol and ammonia.

[Chris Pohl]

Jay-Z

OnGuard II P cartridges will definitely work for this application. If I remember correctly, the capture efficiency for phenolics on this material is a bit better when the pH is <7. The advantage of a polyvinylpyrrolidone based media such as this is that retention is not based on electrostatic interactions so it's compatible with a wider variety of solvent systems than required using anion exchange capture media. On the other hand, as Uwe mentioned above any anion exchange sample prep cartridge should be viable for removal of tannic acid but in this case best removal efficiency requires a pH sufficient to ionize at least one of the phenolic groups (>7).

[SIELC_Tech]

Jay-Z,

Provide me with your email and I will send you a method for the retention of phenylephrine-tannic acid combination. All tannic acids come close to void (0.5-1 minutes) and phenylephrine can be retained longer then 3 minutes even with double flow rate (Primesep 100 column, 3.2x50 mm, ACN/water/phosphoric acid, 1 ml/min). For phenylephrine this translates to over 30 minutes retention on 4.6x150 mm column at 1 ml/min. You can reduce retention time of your target compound by increasing ion strength of the mobile phase.
Contact us if you need more details.

regards,