Chromatography Forum

Hi All

I am busy analysing for Benzalkonium chloride (BAC) in eye drops. The HPLC method specifies that the samples should not be filtered. However, after a few sample injections the HPLC system goes over pressure resulting in my run being “aborted”. I have tried using a guard column but this also blocks after a while. I then decided to reverse the column and backflush the column to remove particles on the head of the column. This appears to be “short term fix” because when I inject more samples, the column goes over pressure again. I was thinking of evaluating a few filter types to see if this would extend my column life and prevent my system from going over pressure. Does anyone know of a suitable filter for BAC? I was thinking of using PTFE or PVDF as starting point.

Any suggestions would be greatly appreciated.

Regards
Mike

Hi Mike,

Beware of advice which has no cost...I found a Thermo Dionex App Note that suggests Millex HV, 0.22 micron hydrophilic PVDF.

http://www.dionex.com/en-us/webdocs/820 ... 2313_E.pdf

There are lots of published methods...only abstracts, unfortunately.

Please see what you think and thank you.

Morning Matt

Thanks for the advice. I'll try this out today.

Regards
Mike

But you can use a centrifuge instead of filters. Most filter will absorb your BAC. Could be that the recommended filter from Matt will work. Give a trial.
Good luck.

You have to filter the insoluble particle in eye drops? wow
Could you maybe tell which one is it, so I will never buy those drops.

I have done a lot of eye drops analysis, and I have never had to filtered the sample solution. I suggest not to use GMF. Celulose acetate propably will be fine.

Hi All

Thanks for the comments thus far. At the moment I'm not sure if the unfiltered sample is causing the increase in back pressure. It may also be that when the sample is injected some excipient is causing the increase in back pressure. The sample is injected "as is". I may have to dilute the sample or reduce the inj volume to extend the column life.

Regards
Mike

Dear Kreall,

When I started at Dr. Mann Pharma in Berlin many years ago we used a photometric method to determine BAC. After Bausch & Lomb has taken over the company and we had a FDA inspection we got a few new HPLC systems and developed HPLC methods also for BAC. So far I remember that was not a simple issue and sample prep was tricky.
When it comes to stability testing it might be necessary to filter the samples. Especially when the samples were stored at elevated temperatures.

Dear Gerhard,
I understand that back in the days the analysis of BAC was challenging. But as far I know in all analyses I have done in eye drops, also using one of the Bausch & Lomb method, there was't any preparation of the sample solution. Inject directly or maybe dillute. I rather centrifuge the sample as You said than filtered it.

For benzalkonium chloride assay by HPLC in a consumer product, we dilute samples with ethanol-water, and filter through a glass membrane filter (Whatman #AV125UGMF) then inject. We do discard the first 1/2 ml or so from the filter before collecting in an autosampler vial, but that's relatively common procedure for us.

Morning All

Thanks for the suggestions. I have many more options since before I sent this post .

Thanks again.

Mike