Chromatography Forum

Hi All,

Just wondering if working for GMP/GLP lab you need to keep a record of how many mm you take off the column length each time you have to cut it?

Thank you

Hello

Trimming and noting column length is impractical.
You can calibrate your GC column using unretained compund - you will find this procedure in GC manuals.
Note that even new column never has exact length - for example 30m new column can have 29.5m or 30.0m

Regards

Tomasz Kubowicz

Tomasz - how would you measure a column's length from the gas hold-up time ?, in actual practice on a current GC.

Peter

Just wondering if working for GMP/GLP lab you need to keep a record of how many mm you take off the column length each time you have to cut it?

My most recent supervisor was of the mindset that one should document EVERY tiny little detail possible under the sun.

Of course, cGMP gives very little guidance on stuff like this, won't even define what "standardize frequently" for Volumetric Solutions means, or if such standardizations should be done in multiple (and if so, how close must the individual results agree?).

Personally, I did not record that I changed changed a GC septum (which I did every day), or stuff like that. I'm not positive that I even recorded the serial number of the column either, but it might have been on our GC software. For HPLC or for GC validations, we did document the column serial numbers and went way overboard, like doing LOD and LOQ for ethanol assay for products that were over 60% ethanol.

Maybe I'll just rot in hell...

I have not documented this in previous GC labs. As mentioned in this thread, there is no official regulation or guidance that states you need to or should do so. This would be controlled at the lab level, so if your SOP states to do so, then you must do it. If someone is trying to add this to an SOP, they should come up with a good reason to do it. Hopefully something better than "I saw this done at another company" which they tend to then translate into "Because I saw it done at this other company, it must be GMP to do so".

Hello

Tomasz - how would you measure a column's length from the gas hold-up time ?, in actual practice on a current GC.

Peter

1.I'd measure holdup time of non retained peak
2.I'd run column pressure/flow calculator. Then I'd increase or decrease GC column length in a column pressure/flow calculator until the calculated holdup time matches the experimental holdup time.

Regards

Tomasz Kubowicz

OK, that should work. I was thinking that the process was circular - you have to know the length to calculate the flow from the pressure.

I wonder how accurate it would be in practice.

Peter

Hi

I can see where both Tomasz and Peter are coming from.

I agree that initially I found myself in some circular arguments but eventually from some back of the envelope calculations

the column volume is pi x r squared x L
For 30m x 0,32mm column this is 2.143 mls but here L is unknown

So the retention time of a non retained peak can be related to 1 column volume/min

Substitution will give the column length.

However, this would require some very precise flow measurement at the outlet and, as Peter says, how accurate would it be in practice allowing for temperature etc

Still, it was an interesting if pointless academic exercise

In answer to your original query I would not record mm cut off in installation etc

As an aside, since I used many columns on various GCs I used to keep a separate log of of each column, attach a number to it and note any major changes e.g. cutting off a few metres. I would also refer to that column number in any analysis reports.

I refused to keep a log of the injections made on that column

Regards

Ralph