EP method for azithromycin

[gerapas]

Does anybody run this method successfully? i an dealing with terrible problems. i run in agilent 1200,1260,1290 LC's with XTerra MS. Backpressure is about 90-100bar. After a while, 40-50min(it's 93min gradient!) or maybe in the 2nd or 3rd injection, i have enormous fluctuations, from 90 bar to 30, then to 80 and then to 5 or even 1 bar, done in seconds. if the backpressure doesn't reach 0 bar, the analysis will continue with instant changes from1-10 to 50-70 bar and after a while it may raise up to 80-90 bar. But this will happen again soon and the analysis will stop unavoidably. I have not managed to run more than 7-8 injections in a row. I've used at least 5 LC's and many columns. If someone doesn't know the method and wants to help, he may take a look at EP or ask me for the conditions.
Thanks.

[HPLCaddict]

Just a guess without knowing the method: pure acetonitrile as eluent B?

[dblux_]

Just a guess without knowing the method: pure acetonitrile as eluent B?

Faulty operation of check valves ?

I was convinced that Agilent pumps have active check valves which are not prone to stick.

I would suggest trying different brand of ACN after sonication of dirty valves.

[gerapas]

eluent B is ACN/MeOH 75/25. It's a 93min gradient with various steps and a low concentration phosphate buffer for eluent A. i have tried 5 LC's, 2 with active inlet and 3 with the common ball type. i wouldn't blame the instrumentation. HPLCaddict, i really would like to know your thinking behind your answer. Have you seen this before? dblux, we use 3 brands of ACN, well known. .no difference whatsoever. is there someone that really run this method? or recognise the symptoms i described and know what the problem may be ?

[dblux_]

eluent B is ACN/MeOH 75/25. It's a 93min gradient with various steps and a low concentration phosphate buffer for eluent A. i have tried 5 LC's, 2 with active inlet and 3 with the common ball type. i wouldn't blame the instrumentation. HPLCaddict, i really would like to know your thinking behind your answer. Have you seen this before? dblux, we use 3 brands of ACN, well known. .no difference whatsoever. is there someone that really run this method? or recognise the symptoms i described and know what the problem may be ?

It's well known problem with some brands of ACN that pumping 100% ACN is imposssible (eg. Dionex LPG 680 pump). However another brand of ACN is OK (Merck LichroSolv gradient type ACN is OK for me even if pumping 100% of ACN).

[gerapas]

Eluent B is ACN/MEOH 75/25, not pure ACN. do you believe that using a binary pump i would have better luck?