Hello everybody!
I´m having a problem with my high speed columns :everyone I´ve tried, produced band broadening and tailing peaks after a few runs.
Now I´m with a microbore one of 5cm x 2.1mm, of 3.5um, C18.I got a flow of 0.4mL/min, maximum; and never had preasure problems .(Never more than 150bar)
The question is if 0.4mL/min is too much flow.Could it have comprimed the silica packing and generated a void volume?

Thank you very much.

0.4 mL/min through a 2.1 mm id column is equivalent to 1.9 ml/min through a "standard" 4.6 mm id column (proportional to the square of the column diameter). Given a length of 5 cm, this flow rate should not damage a 3.5-micron packing.

If you see band broadening and tailing all the time, then I would suspect extra-column volume: injection volume, connecting tubing length/diameter, fittings, and detector cell volume.

I'm assuming that you are taking the usual precautions:
- injection volume down around 1 or 2 microliters
- 0.005" id connecting tubing
- low volume (1-2 microliters) flow cell.

If your efficiency looks OK for a "few" runs (what is "a few" in this case? 3? 10? . . .) and then drops off, I would start off by double-checking my fittings to make sure something hasn't come loose. Then I'd look at my sample chemistry to see if I'm not precipitating something.

Hello Tom,
Thanks for answering so fast...

My English is a little bit limitated, so perhaps I´m going to look too much direct.

I´m filtering water, AcN, and KH2PO4 dsn, and sample, trough 2um; also I´m using an adittional microfilter pre-column of 2 um.
The equipment is being shared with other colleague, who is also working in hs-hplc and she doesn´t have any problems, so I think that fittins, flow cell or tubing connections are not the problem...

I´m ingecting 0.5uL.
I wash every day the column at the end of working, to be sure that nothing is retained .

Really, it has happend to me with another conventional column too(I didn´t supered 2mL/min).
So I´m thinking about the possibility of a bad packing system...

bad packing system? Do you pack the columns yourself?

No, of course, not.
But it´s been a year with a lot of problems with the columns from the same company.
I cant find other explanation....Do you?

How do you wash your columns, what kind of samples do you inject?

Is you wash strong enough?

I wash the column everyday .I start with water and 5%AcN for almost half an hour; after, I go to 100% AcN and I´m there for 10 to 15 minutes and at the end, I equilibrate the column in 65 %.
It´s a C18.
But today, I discobered that if I put 100%AcN after the washing, something eluted...
Do you know other way of washing better?
Thanks...

I inject basic antibacterials...

Have you tried a wash with THF already, this sometimes may help

In one of the 'HPLC Troubleshooting' columns in the magazine there was an instance of a chemist using PEEK tubing that 'slipped' under high pressure, generating a void volume after a few injections.

I have hundreds of runs on a column that runs over 200 bar, but I have metal tubing on the inlet side--no possibility of slippage.

There are many possible reasons, but this one is easy to eliminate.

If junk from your injections is a suspected problem, how about using a guard column?

Every conection is of steal; The only thing I use of peek are fingertight of high preasure...
I´m trying with a precolumn..
Thank to everybody..
Regards.