mobile phase too sticky...

[1199326]

We have problem when analysis pefloxacin mesilate using EP method, the mobile phase states: 30 volumes of acetone, 70 volumes of 2.70 g/l cetyltrimethylammoniium bromide and 6.18 g/l boric acid pH 8.30 (exactly adjusted to pH 8.30 with 1 M sodium hydroxide), and 0.2 volumes of thiodiethylene glycol.

Due to the stickness of this mobile phase, we have problem pumping into the detector, blockage occurred quite often..

Could anyone please suggest me if there is any way we can solve this problem?
Thanks!

[zokitano]

How about, to avoid these kind of methods?
Have you looked for analogous method in USP?
Or another simpler validated method for the same purpose?

[1199326]

yeah... That's quite a good idea... however we are currently registrate our product in EU, therefore comply with EP is a must..

[Consumer Products Guy]

I'm assuming that you pre-filter the mobile phase before using (that's "a must"), and the stickiness you mention is high viscosity of the mobile phase? If so EP, like USP likely allows some flexibility of your conditions (without doing validation studies, see USP <621>) which can help lower your pressures. This could include reducing the column flow rate or increasing column temperature.

If the high pressure occurs after pumping for some time, then the reason is likely buffer precipitation clogging the inlet frit. If the pressur eincreases after injecting a bunch of samples, then filter those as well, and/or something in your sample is causing that.

We've had certain samples even when filtered, would build up in the column and start to increase pressure after a certain number of injections; our solution was to precipitate those and filter out before injecting.

[dorota]

For some mobile phases we use a heating bath, for example: http://www.ika.net/owa/ika/catalog.prod ... Subgroup=1

[1199326]

Thank you all so much for the helpful tips... I'll try out and let you know how it goes!!

[ognjanovic.stefan]

We are also having problems with this EP method. They started when we had to use a new column, first we couldn't achieve resolution, so we played with mobile phase composition (different T and pH) and finally got it. But now the repeatability is a bust (RSD(imp F) = 10-15 %). It's strange since it's a very old method, we tried several different new column LOT numbers, we use the same chemicals and the method just doesn't work. How did you solve your problem? Pressure rises each injection by 100 psi even when injecting mobile phase.