Chromatography Forum

Dear Friends,

I would like to get your help in dealing with this problem. I am finding that propyl paraben gives only 70% recovery values in the analysis of some pharma products that contain a complicated matrix (API, excipients, Xanthan gum, etc). However, Methyl paraben gives recoveries very close to 100% in the same experiments and solutions, and same sample preparation.

I have some ideas about what is happening and how to overcome the problem. But I would like to know if any of you have specific experiences with these kinds of problems. perhaps I can solve the problems faster with your help.

Do you know of any references dealing with matrix problems like these?

Thanks.

Benjamin

What is your dissolution solvent? We've had 100% recovery on both, from various types of products, and no assay issues.

Dear Consumer products Guy,

The solvent currently employed is 20% Methanol/H20. Can you tell me something about your conditions?. Perhaps is all a matter of adjusting polarity. I would like to get results like yours.

Thanks,

Benjamin

Maybe it just sticks somewhere by hydrophobic interaction. How about increasing the methanol content?

For parabens and other phenolics, we use acid modifier in the aqueous portion of our mobile phase. This could be phosphoric acid, acetic acid, or an acidic buffer (maybe pH 3 or 4). We normally use acetonitrile as the organic portion of the mobile phase but have used methanol as well in the past. We dissolve our samples in methanol and filter. Propyl paraben can also kick out of products such as lotions (as a gritty solid) if formulation and/or processing is borderline; we've observed that numerous times.

Benjamin,

We have a number of test methods for parabens analysis for toothpaste and mouthwash products. The mobile phases use 30-50% methanol or acetonitrile and either water or a buffer. Columns are either C8 or C18.

I would agree with the comments of others that you should try more methanol in your extraction solvent. It seems that the propyl paraben needs a higher organic content for good recovery. This is especially true since you have Xanthan gum in your formulation. We have that in some of our products and it always tends to complicate things a bit and we need a higher percent organic whenever the gum is present.

Regards,
Dan

Dear Friends,

Thanks to you all for your comments. I will try your recommendations.

Benjamin