Chromatography Forum

Hello,

Can some body explain. what causes changes in area from injection to injection.

I looked for air bubble in the injector. ( looks good)

pressure is good. Looked for leaks and check valves fine.

I use methanol as diluent. Does it cause any vapor pressure issues in the closed vials.

Previously i read that it is a good practice to saturate the column with the drug ( by injecting more injection volume than method). --- can some body explain how this is helpful.

thanks

subha

What instrument/injector/autosampler are you using? Suggestions usually are better if they are instrument specific.

When was the instrument last calibrated or had preventative maintenance performed? If there is a seal in your syringe, that needs to be replaced at least once a year. Other suggestions will be instrument specific.

Is there a rinse programmed? rinse strength and organic component make a great deal of difference in the analysis, depending on the compounds.

Wanda

Only fill autosampler vials half-way up.

Subha,

Believe it or not, changes in area can be divided into at least 3 different events:

1. Increasing areas.
2. Decreasing areas
3. Unpredictable variation

Each of these 3 events would have its own reason. So I think you need to log some more specific information in order to get a specific answer/suggestion.

Best Regards

Unless you are only injecting a small amount (less than 10ul) it is not agood idea to use methanol as the solvent.

The solvent should have the eluting power equal to the mobile phase, or less, to avoid peak broadening

Hi,

When there is a variation in area from the same sample injected 2x or more, I usually readily check my autoinjector,perhaps there is some clog in the needle seat.Rinse and purge the autoinjector so as to remove some clogging material there. Inject same sample 3x or more to see if you got a consistent area.What HPLC brand are you using?