Chromatography Forum

I am posting this issue as a headspace novice, and with some GC experience.

Recently a GC head space method has been developed and validated by a contract lab using a Perkin Elmer (HS 40) instrumentation. However, the headspace sampler(G1888) and GC here are made by Agilent.

I have just learned that Agilent headspace systems employ pressure loop system for sampling, whereas Perkin Elmer employ balanced pressure system. I have received the parameters that were ran with the Perkin Elmer -


Sampler Shaker On
Incubation Temperature 85 oC
Needle Temperature 110 oC
Transfer Line Temperature 110 oC
GC Cycle Time 47 min
Incubation Time 60 min
Pressurisation Time 1.5 min
HS Pressure (He) 16 psi
Injection Time 0.10 min
Withdrawal Time 0.5 min
Vial Venting Off

Is there a way of 'converting' these parameters so to run the method on the Agilent headspace sampler, or to show equivilency between the two.

Your question is reasonable and I wish there was a simple and straightforward answer.

When transferring a validated method to a different lab is it not reasonable to expect that regulatory officials would require a demonstration that the lab is capable of performing the method as validated before any results would be accepted.

Since your lab does not have the same equipment, nor any equipment that is of the same design, would a revalidation of the method also not be expected?

There are factors which can affect the performance of the method beyond the timing of certain events such as heating time of the HS vial.

For example: Injection time and loop size do not have a simple conversion formula as pressure and flow can change the effective sample size placed upon the analytical column.

Transfer lines and needles can be of different materials and thus temperatures suitable for one instrument may not be acceptable for another.

Hindsight is so clear but forgive me as I state the obvious, when you contract a lab to develop a method you must dictate the equipment that is going to be used in that method. Otherwise, it requires a full validation from scratch.

The first method does give you a good idea about heating times, sample size, and pressurization of the vial before sampling, but there are many other factors such as carryover from the Agilent valved sample system which come into play.

best wishes,

Rodney George
consultant

I am going to have to disagree with the last post. I was reading this with hopes of a comparision between the two systems till I read the response........
T
he first question is if the method was validated using the guidlines in the ICH, which it should be. This is the accepted methodology for method development and validation. This ensures the method is robust enough to withstand an analytical transfer of methods to like instruments.
If your contract lab performed it this way (ie the right way) all you need to do is do some research on the parameters of the autosampler, and verify the method. This is the same thing that is done with compendial methods, such as in the USP and EP. You should never have to re-validate a method on method transfer, if this is the case you need to switch contract labs immediately.

What you need to do is ask your contract lab about this. Is the ICH referenced in the report? Have they performed Robustness and altered all parameters? Did they have a second analyst attempt accuracy/recovery? You can get the ICH online and check it out.

I am not trying to get on a high horse here but this is very important, my lab has been hit hard by this on several occasions before. I work for a contract lab, we now perform every development and validation by ICH guidline for external customers and internal projects and after the switch we have little to no problems.

If you are having problems with validated methods let me know and I can email you my information.

It will help a great deal to understand the differences between the two injection systems. I believe Restek has some documents on different headspace techniques, with pictures and flow diagrams, and that may help a great deal.

Like you, I know some GC, but not much headspace, and I have looked at this situation before (and have seen it done badly by others). Spend a little time educating yourself, and it will get easier.

I can say that most of the temperatures should translate easily (oven, transfer line). The Needle temp should probably become the Loop temp. For the Agilent system you need a vial pressure, which is probably the HS pressure. Inject time should be about 1 minute. The Agilent documentation should have a discussion of "typical" parameters as well.

The other sticky issue is how your HS connects to the GC - through the septum, or in-line with the carrier. This will affect things like split flow, carrier flow, etc.

Read up a little bit and post some more questions and maybe we can help.

We do the transfer method from the API site to the tablet site manufacture. It is good no? The system suitability met was, me keep the regumalators happy, yes, no?