Chilled Diluent

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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I have a method which is currently being verified and there is one impurity peak that grows over time. An analyst ran an experiment, which they chilled the sample diluent in a fridge, pulled it out of the fridge, and diluted the sample to volume in a volumetric flask. They then chilled the autosampler to 5C. I have never used or heard of using chilled diluent and diluting a sample to volume without letting diluent warm to room temperature. The impurity peak was then found to be stable.

Has anyone ever heard of using or used chilled diluent for HPLC impurity testing? I don't want to dismiss the idea, but all my training to date has always told me to let the solution come to room temperature.

Thank you

Running "unstable" samples at low temperature is not uncommon (that's why they make autosamplers that will run at sub-ambient temp). I've never done it myself, but in this case the justification (that it slows degradation) makes sense.
-- Tom Jupille
LC Resources / Separation Science Associates
+ 1 (925) 297-5374
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