Dear chromatographers,
I am doing analysis on HPLC system. Daily I am injecting 60 samples with run time of about 15 mins. My mobile phase contains buffer methanol mixture.If for next few days I have to analyse the same samples which option should I prefer?

1) Condition the column with water followed by organic solvent followed by water and then again start with mobile phase
or
2) Condition the column with water and then again start with mobile phase
or
3)Keep the column in mobile phase itself in lower flow rate after completion of injections.

Thanks.

Personally, in my lab I'd try using suggestion #3, it's the easiest, likely most robust way. If you flush with just water, make sure you know what you're doing, some phases may de-wet or "collapse", requiring additional equilibration.

I would agree with anon above. If you do not have to change the conditions within the column, you are better off. Leave it at a low flow rate, say .1-.2 ml/min and then equilibration for the next run will be short.

I would use a modified version of #1. It is usually a good idea to flush strongly retained impurities from the column.

I would rinse the buffer salt from the column with 20 column volumes of 20% methanol in water. Then clean the column with 10-40 column volumes of methanol. Lower the organic concentration with 10 column volumes of the 20% methanol then back to mobile phase. If you have a quaternary system you can just put the 20% methanol on an unsued channel and automate the whole thing. Of course you could use mobile phase with water substituted for the buffer as the rinse solution.

Try it once, if nothing or very little elutes from the column then you are probably safe with #3 as long as nothing (like water quality) changes.

We have been using a system similar to #3 (without premixed mp) for over a year with no problems. Anonomous 3.... If there were strongly retained impurities then the original method would not be very good.

Hi John B, why do you say that? I'm not talking about sample related impurities. I'm talking about very low levels of organic impurities that make it into the mobile phase from the water, reagents, glassware detergents, etc. These can accumulate on the column and then affect the separation.

If you are not having a problem then I guess there is no need to go looking for one, but an ounce of prevention ...

Hi, I'm tryin' to challenge our high rate of failures in our Lab.
One of the issues come out is about how analysts wash the instruments between different analysis/mobile phases.
can anyone tell me
- what should be the best practice (considering they're always on a hurry)
- which are the main things to avoid in mixing different products on the same hplc?

Thanks in advance

If possible dedicate columns for specific analysis. This avoids the above issues. I realize this can be expensive.

Preferentially, you do not want to run normal-phase methods and reversed-phase methods on the same instrument, since you have wash the instrument forever to get rid of water. Amoung reversed-phase methods, wash the instrument free of salts after each set of analyses. Otherwise, I do not see any problems with the instrument.