NaBenzoate new method?

[bgiles]

We are trying to separate Na Benzoate in a drug product unsuccesfully. We have tried variations of the ACME 50% buffer pH 3.0 and 50% ACN on C18 columns but there is considerable co-elution with the API. Is anyone familar with an alternative method for Na Benzoate?

[juddc]

You can do a few things:

First thought would be to raise or lower the amount of ACN in your mobile phase to see if you can obtain a reasonable separation.

If that's not successful, try using a different solvent such as MeOH to alter your column selectivity.

Third option would be to raise the mobile phase pH to about 5.5 (with ammonium acetate) and separate the benzoate as a salt using much less organic in your mobile phase. Benzoate will be retained on most RP columns using about 3-10% organic in the mobile phase. I've used this approach successfully to separate benzoic acid from sorbic acid in a number of matrices.

If no luck there, then on to different RP columns (C8, C18, Phenyl, Pheylhexyl, embedded polar phase vs std type column, etc...) trying all of the above until you get it right.

[Dan]

bgiles,

I second the notion of trying another column type. You could get the selectivity that you need.

I have seen separations of Na benzoate and parabens using both phenyl and CN columns with a mobile phase similar to yours, but with 60-70% buffer. The samples were liquid drug products, but should work for solid dosage forms also.

Regards,
Dan

[Uwe Neue]

Packings with an embedded polar group such as any of the packings from Waters with an RP designation (SymmetryShield RP18, XBridge RP18), will give a different selectivity for acids. However, on the short term, the fastest approach is to go to pH 4.75 with an acetate buffer, unless you need to work at low UV for reasons of sensitivity.

[SIELC_Tech]

You can also try two dimensional approach with mixed mode phases:
http://www.sielc.com/Technology_2D_Properties.html

Compounds are retained based on two mechanisms reverse phase and ion exchange. If your drug is basic you can use Primesep 100 column and retain it based on reverse phase and cation-exchange mechanism, if your drug is acidic you will retain it based on reverse phase and anion-exchange mechanisms. You can also play with pH to change ionization state of stationary phase and components in your analyte.

You can change retention order by changing buffer nature. See effect of TFA vs. formic acid on retention of benzoic acid:

http://www.sielc.com/compound_010.html

Contact me if you have questions.

Vlad

[james little]

Could try THF, gives a lot of different specificity compared to Acetonitrile and methanol.

Use a C18 column and 0.1% phosphoric acid in water, start at relatively high aqueous, maybe 75-85% organic or possibly higher?

[Consumer Products Guy]

As James Little stated, I'd start first by adding maybe 10% THF instead of some of the acetonitrile, start with that. If you stay as close to your original procedure, you may have less method verification to do. My second choice may be an intrinsically base-deactivated column. Keep the pH low with your buffer or some acetic acid to protonate to benzoic acid like you're doing. I've also done this by GC, but my bet is you'll be able to make it work with HPLC; understand you can't really disclose identity of your API.

[jtreacy]

Something like a Prevail organic acids column should work fairly well for benzoic acid. A mobile phase of something like 90% 0.1% formic acid 10% ACN should do it.

If you want to make it more difficult for yourself you could derivatise it and make the phenacyl ester which is easy enough to retain on C18 and has massive sensitivity

John

PS if you use THF in your mobile phase make sure you use the unstabilised stuff. Butylated hydroxytoluene will precipitate on mixing with the aqueous phase and 'knacker' everything in its path

[Cliff Mitchell]

I would try changing the pH to a higher value. Phosphate at pH 7 or acetate at pH 5 (like Uwe suggested). The benzoate will be retained much less when it is ionized.

Cliff

[DR]

I would try changing the pH to a higher value. Phosphate at pH 7 or acetate at pH 5 (like Uwe suggested). The benzoate will be retained much less when it is ionized.

Cliff

unless you're using a SCX column

[danko]

Hi guys

How do we know that the benzoate needs to elute earlier in order to be better separated from the API?
It could be the other way around. Sometimes there is not enough info………………………

[juddc]

It doesn't really matter which way it goes as long as it moves away from the API. Raising the pH from 3 to 5-ish will definitely reduce the retention of the benzoate on the column. What it does relative to the API is anyone's guess and I don't think anyone's made any concrete predictions there. This thread points up the power of using pH to manipulate a separation

[Bryan Evans]

You can try these conditions:

http://www.imtakt.com/TecInfo/TI033E.pdf
http://www.imtakt.com/TecInfo/TI034E.pdf

[ym3142]

To: juddc, Cliff Mitchell, Uwe and every else who intends to use pH 4.2+/- 1:

Did you experience the Benzoic acid behavior around pH 4.2?

is it in both forms of the acid and the benzonate?

is this the reason for benzoic acid to give tail peak, which was observed in our lab?
Thanks

[ym3142]

To: juddc, Cliff Mitchell, Uwe and every else who intends to use pH 4.2+/- 1:

Did you experience the Benzoic acid behavior around pH 4.2?

is it in both forms of the acid and the benzonate?

is this the reason for benzoic acid to give tail peak, which was observed in our lab?
Thanks