Chromatography Forum

Hello every one,

We are facing very poor column life time, during HPLC method development of pH range 6-10. Even we are using hydride silica like Water x-bridge, X-terra.
We well known that natural silica is soluble in basic pH ranges, is it applicable to Hydride silica?. But, column manufacture are given 1-12 pH range. Please your experience how can i improve the column life time in the pH range of 6-10.

1) Which make HPLC column is giving long life time in particular pH range.
2) What are the precautions we have to take to maintain the column lif time long.
3) How many minimum injections can be expected with this particular pH range.

Please give any suggestion.

Regards
sreenivas

First of all: On what basis have you concluded that the pH is the “devil”? Please describe what happens and if the assumed damage is permanent or the chromatography “goes back to normal/acceptable when you lower the pH under 6.
Secondly: If the higher pH causes the trouble, then it does not make sense to ask how many injections you could expect the column to withstand. You assume that the mobile phase degrades your column material so you should ask yourself: how long can I have mobile phase of a given pH running through my column before I dies.
Lastly: Remember that the temperature is an important factor in this context - the higher the temperature the faster will the silica dissolve at a given pH.

Best Regards

Why are you using high pH in the first place? What is your reason for pH 10? If it is to keep basic compounds on-ionized and retentive on the column there are other ways to do this.

To expand a bit on Danko's post, if the column is deteriorating relatively quickly (say, within a day or so), you can determine whether the problem is the mobile phase or the sample by running a "punctuated" series of injections. There is a brief summary of the technique on our web site: http://www.lcresources.com/resources/TSWiz/hs390.htm

When doing method development do you use one given C18 column at different pH values, with different buffers and mobile phase compositions? That means stress to the column and will shorten life time.
If a high pH is needed, I would recommend to use a Polymer based C18 column. They are better than their immage. The columns you mentioned are working well and with high numbers of injections if they are only used for a given mobile phase and a given pH.
Matrix, purity of the samples/standards playing also an important role. I saw customers who killed their column with only one injection of a sample, and I saw others who did 10.000 injections on one column. Special tested columns for well defined applications are available on the market with guarantee from the manufacturers that x numbers of injections can be achieved. For standard HPLC columns it might be impossible to tell a customer the number of injections he can achieve with the column.

The only reason to use high pH is to have basic compounds non-ionized. The issue can be addressed with lower pH:
http://www.sielc.com/upload/file/pdf/SI ... e_2005.pdf