by
Dan » Fri Jan 18, 2008 3:07 am
My comments below are from the perspective of working in a cGMP environment.
Any injections that take place before the system suitability test (SST) injections would not be valid and can only be used "for information only". So, the injections of diluent and limit solution in your sequence are not valid (unless the limit solution is part of your SST).
I have seen many sequences with injections that are for info only. Examples: a test injection of a standard, a diluent injection. People use these injections for checking to see that the instrument is working OK before the actual run starts.
If the method calls for a diluent injection, then run it after the SST injections. I think that a diluent injection is always a good idea even if the method doesn't call for it.
What are "standard 1" and "standard 2"? Is one the calibration standard and the other a check standard? Or are they both calibration standards? The answers to these questions will determine the proper injection sequence.
Are the "duplicate" stability samples duplicate preparations or duplicate injections? There was another discussion thread about duplicates that you may want to look at.
Here is an example of an injection sequence that I have used:
1. Test (standard) injection
2. Standard injection times 5, for SST (this is usually standard 1)
3. Check standard injection (this is usually standard 2 and it is for a standard check/recovery not for calibration)
4. Limit (or resolution) solution (if called for in the method)
5. Calibration standard (usually standard 1)
6. Sample 1 (one injection only)
6. Sample 2 (one injection only)
(going by the SOP, only 6 samples can be injected between bracketing standards)
7. Calibration standard (again, this is usually standard 1)
8. next sample and etc......
The two calibation standards are used for bracketing. However, you can use all of the calibration standards throughout the run for calibration pruposes (i.e. an overall standard calibration approach). Some methods have called for a separate resolution solution, This is usually when there is only one API in the drug product so the standard injection shows only one peak (although, I once saw a method that had a resolution requirement for the one peak in the standard; people couldn't understand why that doesn't work especially as the FDA accepted it! (But that was a while ago, it wouldnt' fly today)).
You can have more than one calibration standard in the sequence. It all depends on you method. The sequence above is for a simple method with only one calibration standard and one check standard.
How and when you inject your limit solution depends on what is stated in the method. Usually, I have seen a limit solution only injected once as I noted in the sequence above.
Regards,
Dan
