Chromatography Forum

Hi there, we were running a residual solvent validation (intermediate precision) and the gc stopped, we got it going again, but it was two days later. The samples and standards originally prepared were run. We have no sample or standard stability data. Will this be an issue. We prepare the samples in the gc vial directly, and therefore I am at a loss how to determine stability.

I would appreciate any help on this matter.

Thanks

Scio

did you not run any samples or standards before it stopped?

Are there any differences in the stds before and after the stoppage?

Or were you samples and stds all run after the stoppage? If they were I would not consider the run worthy to be included in your validation.

I would not throw out the data however if after your validation it shows the data collected was accurate. It gives you some proof to ruggedness in the future if a run stops in mid-analysis.

best wishes,

Rod

I think GC vials are too small to precisely prepare standards

I think GC vials are too small to precisely prepare standards

That depends how you do it, and on the volume of the vial of course - a residual solvent method could easily be using 20 ml headspace vials.

On the validity of the delayed analyses: you do not know that the standards and samples are stable, therefore you do not know what their concentrations were when you ran them, therefore they cannot be used to validate the method, except, as Rod says for ruggedness (which someone might thank you for one day if their GC stops in the middle of a batch ).

Peter

I think GC vials are too small to precisely prepare standards

That depends how you do it, and on the volume of the vial of course - a residual solvent method could easily be using 20 ml headspace vials.

On the validity of the delayed analyses: you do not know that the standards and samples are stable, therefore you do not know what their concentrations were when you ran them, therefore they cannot be used to validate the method, except, as Rod says for ruggedness (which someone might thank you for one day if their GC stops in the middle of a batch ).

Peter

I always thought GC vials are normally 2ml which fit into all the ALS
HS vials are different and I don't think we should prepare STDs in them, but proper glasswares.

thohry

As Peter has said, it depends upon HOW you prepare them.

But without going into classroom mode here without any props, let me only say that you can weigh liquids much more accurately than you can measure their volumes. Volumetic flasks have a 1% accuracy as do most pipettes.

A good analytical balance improves on that 1% error by a huge amount, no?

Peter is correct in his statements. and by the way:

Headspace vials can be of 20-22 mL, 10-12 mL, 5-7mL, or approx. 1.8mL volume.

best wishes,

Rodney George
consultant