Number of Preparations & Injections for each sample

[Terry]

Dear all,

One of our history HPLC test method specify an injection sequnce like this:

Blank 1 or more injection until the baseline is stable
Standard 5 injections
Check Standard 2 injections
Sample 1 preparation 1 2 injections
Sample 1 preparation 2 2 injections
Sample 2 preparation 1 2 injections
Sample 2 preparation 2 2 injections
Bracketing Standard 1 injection

We are considering change the number of injection for each preparation from 2 to 1, it will save us a lot of time. Then the sequnce would be:

Blank 1 or more injection until the baseline is stable
Standard 5 injections
Check Standard 1 injection
Sample 1 preparation 1 1 injection
Sample 1 preparation 2 1 injection
Sample 2 preparation 1 1 injection
Sample 2 preparation 2 1 injection
Bracketing Standard 1 injection

My question is: which sequence do you prefer, while it still meets regulatory requirement?

Thanks,

Terry

[Klaus I.]

I presume that you are doing chromatography in a non-bioanalytical area.

As far as I know, double-injections were routinely performed for manuel injections only (just like the using of internal standards). A state-of-the-art hplc system includes an autosampler with an excellent accuracy. Therfore a single injection ist the usual procedure.

[t_morris]

Other than what was added by Klaus I., I would have two check std injetions to provide a better correlation of standards. Depending on you peak and baseline noise, an average of two can make the difference.