Chromatography Forum

hello guys
we are working in a phamacuetical company where we do analys ophthalmic suspensions & drops ragularly,
here have a preservative Benzalkonium Cl almost in all ophthalmics, we use CN cloumns for the analysis of benzalkonium cl,with MP water(pH-2.2):ACN:IPA
my Question is that, is there any other mothod is available for the analysis of BZCl,which is more reliable than the above method????
thanks

Hi

As i recall this one pops up now and then. I suggest trying using the search function, maybe restricting it to LC and you should find a number of threads on the topic.

you can also chech pharmacopieas like USP/EP/BP/JP etc if there are different procedures around.

we are working in a phamacuetical company where we do analys ophthalmic suspensions & drops ragularly,
here have a preservative Benzalkonium Cl almost in all ophthalmics, we use CN cloumns for the analysis of benzalkonium cl

Your problem is that you've been using the USP assay procedure, or one derived from it. And it's junk.

All I can say (for proprietary/trade secret reasons) is that we use a C18 column for benzalkonium chloride and separate the individual C12, C14, C16, and C18 peaks. That's why the company pays me big bucks. I cannot divulge more information.

I used to assay this on a regular basis quite a few years ago. From memory a Synergi Polar RP gave better peak shape and resolution than a CN. Its a long while ago but I think it was an acetonitrile/ Sodium acetate mobile phase (pH 4.5 ish). it could generally control from C8 and upwards in terms of homologs. The only problem from memory is sensitiviity I,m guessing in an opthalmic you'd be using BAK at about 0.02%w/v I found at 283nm you really needed a large injection volume ~250µL at least for it to work.

I have analysed these substances and I have two suggestions:

- Use EtOH in sample to get consistent peak areas (otherwise you will see drift of peak areas due to the surface activity).

- Use either a mixed-mode (anion exchange + reversed phase) column like Primesep D, or a positive ion-pair (like TEA). This will give ion-exclusion of the peaks, which improve the peak shapes a lot. I have tailing factors of 1.0 in my system for all homologues.