By Anonymous on Thursday, June 24, 2004 - 08:27 pm:

Hello, everybody!

I need to analyze low level Cetylpyridinium chloride (0.1%) in a syrup kind sample by HPLC.

The sample also contains Tannic acid (7%), Benzocaine (20%), Benzyl alcohol (4%), Alcohol (24%) and some flavor, dye, oil etc.

The mobile phase is Acetonitrile: water (900:100) plus 5 mL ion pair reagent IPC B6. Phenomenex Primesphere 10u 4.6mm x 250mm column. Wavelength 259nm. Diluent: Acetonitrile.

This condition does not work. Firstly, CPC elutes too early at RT.2.3 min.. Secondly, there is a huge peak very close to CPC peak, and resolution is poor. Thirdly, there is a small peak underneath of CPC peak.

I do not like to use IPC B6. It needs long long time to equilibrium column before run and rinse column after run.

pKa value:
Benzocaine: 8.5
Tannic acid: N/A (pH 3.5)
CPC: N/A (pH 5-5.4)

Can anybody tell me what the problem of my HPLC condition is? Can you give me any suggestion? Thank you in advance!

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By Constantin Sychov on Friday, June 25, 2004 - 04:39 am:

No wonder - it is very-very old method, and really ancient phase.

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By MG on Monday, June 28, 2004 - 11:36 am:

I don't see a flow rate, but if you are running at 1 mL/min, your peak is unretained on that column, or nearly so. What happens if you reduce the acetonitrile content? You should get improved retention and resolution.

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By Anonymous on Wednesday, June 30, 2004 - 08:16 pm:

MG, thanks for your great input. I was running at 1 mL/min. You are right, reducing flow rate and Acetonitrile content maybe the first things to try.