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Single or double injections?
Posted: Wed Aug 17, 2011 12:26 pm
by max_planck
Does anyone know, if there is a regulatory rule on single or double injections using HPLC within the pharmaceutical industry? So far I always worked in GMP/FDA labs that used single injections until I started in my current company where double and single injections of standards and samples are the rule. I am asking because I would like to change this to single injections in order to save time and solvent. Is there a rational for single or double injections?
Thanks for your help!
Re: Single or double injections?
Posted: Wed Aug 17, 2011 2:10 pm
by DR
<-- in pharma
We establish system suitability with 5 or 6 standard injections and a blank, then we start on samples (single injections) and periodically have another standard injection after each group of samples.
For validation of a method, we usually go for triplicate injections of triplicate preparations.
All you get from duplicate injections is a bunch of additional questioning as to how/why you treat the pairs of results. In my opinion, no good can come from it.
Re: Single or double injections?
Posted: Wed Aug 17, 2011 3:07 pm
by juddc
I'm not in a GxP environment, but I do something similar to what DR does. Once system suitability is established, there are no replicate injections of samples.
I will do replicate sample preparations, but that varies with the degree to which the assay is developed. The earlier the assay is in its development, the greater the number of replicates. Yesterday I was working on a new assay with an SPE step in the preparation and everything was done in triplicate. (Amusingly, the sample to sample variation was less than the system suitability %RSD for that one...).
For assays that are validated, I'll typically do one replicate preparation for every 5 samples.
Re: Single or double injections?
Posted: Wed Aug 17, 2011 3:53 pm
by lynzjm
I used to work as a validation and stability study director in a formulation analysis department and whether we used singlicate or duplicate injections depended on the results of the trial method assessment and the validation. If we had a solution generally the repeatiblity (assessed with 6xstd injections %RSD) was good enough to only need singlicate injections, however if the drug formulation was a suspension and had a poor %RSD we would use duplicate injections to try to minimise any erroneous results. Again it was entirely dependant on the development process for each individual formulation. If you are doing standard analysis with the same method etc and have good repeatibility I wouldnt see an issue with cutting down on your standard/sample duplicates. A good way to check system repeatibility and drift as well is to compare the 1st and last std injected.
Generally our runs for finalised methods consisted of;
std1
std1
std1
std1
std1
std1
std2
std2
sample
sample
sample
sample
std2
sample
sample
sample
sample
std2
etc:
with %RSD on the 1st 6 std1's and std comparison checks on the last two std1's and the 1s two std2's. If there was system drift issues we'd compare all the stds throughout the run.
Lynz 
Re: Single or double injections?
Posted: Wed Aug 17, 2011 6:25 pm
by max_planck
The samples we use are suspensions such as eye drops, containing preservatives etc, therefore it makes sense to apply duplicate injections. But I will get rid of the triplicate injections.
Thanks a lot for all your help!