pressure upper limits

[serap g]

dear friends,

I have a great problem with pressure, after 10 injections of fexofenadine standard, pressure increased 180 bar to 280 bar. and although I cleaned the column with ACN/Water the pressure wasn't decreased.
I cannot able to understand this problem, please help me...

I'm working with fexofenadine HCL.
my column is ; inertsil ODS3 3um 3x100mm
my HPLC conditions are;
flow rate 0,6 ml/min
pressure 180bar
column termostate 50C
injection volume 70 ul
mobile phase
%80 (%1 triethylamine solution pH:4,4adjusted with ortophosphoric acid)
%20 Acetonitrile

[Mattias]

The column is probably gone, so invest in a new or change the inlet frit.

Have you tried to premix the mobile phase? Are you using an Agilent system (pump G1311A or similar)?

[Bryan Evans]

Are you filtering your samples / mobile phase?

1% TEA?

[serap g]

first of all thank you for your attention

I thought so, that column was gone but,that column was new, those were the first injections

I wonder that why you asked my system, is there a problem because I am using Agillent 1100 series and my pump is G1311A, otherwise have you got a problem with Agillent pumps?

[serap g]

dear Bryan

yes I'm filtering my samples with 0,2 um PTFE filter, and my mobile phase with 0,45 um filter.

%1 TEA: prepared with water (v/v)

[Bryan Evans]

The TEA is typically used as a competing base to help with peak shape. Its usually necessary for older types of silica based columns - probably not necessary for the newer type of column you are using. It can also reduce column lifetime.

The H3PO4 / TEA is a poor buffer system. You may want to try 0.1% acetic acid and see how that works.

If you are seeing an increase in pressure - try running mobile phase through the system without the column - and see where your baseline pressure is. You may have a clogged in line frit .

[HW Mueller]

What is the matrix of your standard?

[Dan]

1) You don't mention the composition of your sample solvent. If the sample solvent is 80% aqueous like your mobile phase then you must be having a hard time to filter your samples using that 0.2 um PTFE filter. It is possible that you have to force the sample through that filter. That can cause the filter to fail and let particulates through. Those particulates are clogging your column head.

PTFE is not the choice for an aqueous (or mostly aqueous) solvent. Try nylon or PVDC instead. Also, you may not need 0.2 um; using 0.45 um should be suffient.

2) You don't mention how you cleaned your column. If the frit at the head of the column is clogged, you may be able to clean it by flushing it backwards. Turn the column around (DON'T connect it to the detector) and flush backwards. Sometimes this works; sometimes it doesn't.

3) I second Bryan's comments about the TEA. Using TEA has caused me nothing but problems in the past. With today's columns, you don't need it. Yes, it is not suitable for making a buffer.

Regards,
Dan

[Mark Tracy]

Agilent pumps have a filter built into the purge valve on the pump head. Try changing that.

[serap g]

thanks all of you

my matrix is mobile phase so the sample solvent is 80% aqueous,and I'll use nylon filter may be PTFE was caused clogging, but I should use 0,2 um otherwise sample is muddy.

I was checked my system's pressure, all the parts; also frit was changed.

today,I'll try 0,1 % acetic acid solution, probably TEA was caused the pressure increasing.



Regards,

[HW Mueller]

If your analyte matrix is pure mobile phase where does the mud come from? Is it precipitated analyte? You are filtering out most of your analyte? Part of the rest precipitates on your column frit?