Does a standard of a compound show diiferent chromatogram with different system
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Answer:
I think this question needs to be broken down a bit. Is it correct to say that what you really want to know is 'are the two samples different'? Or even does sample A have more of compound X than sample B? (Or maybe this second question asked for several compounds?) So, if it were me I'd start by looking at a single peak, which represents a compound which you think might have different concentrations between treatments, then quantify the variation in the amount of that compound using either peak area or height. So in order to know whether two treatments are different I'd need to know how much variation there is between replicates of the same treatment (different flasks, NOT samples from the same flask). This variation contains variation from at least (i) HPLC run (machine error, probably small) (ii) subsample from a single flask (your pippetting error, and heterogeneity in the flask, also probably small) and (iii) actual differences between replicate flasks. If you think the difference between the treatments is large compared to the difference between replicates, then two replicates of each treatment may be enough, so four flasks. Just be certain that you have true replication, and that the only difference between the the two sets of flasks is the 'treatment' in question. Controls are also good - you might want to run another four flasks without any biology in them - so you know whether it is an effect of the treatment alone, or the effects of the biology that you are seeing (this depends on what a 'treatment' is in your case). And, if the differences between treatments are not large, you'll need more than two replicates, which I'd recommend anyway, but this depends on your resources. If you do not replicate, you cannot know where the differences between your chromatograms come from.
Answer:
☑ By comparing each peak's retention time [tR] with that of injected reference standards in the same chromatographic system [same mobile and stationary phase], a chromatographer may be able to identify each compound. ... The same volume of sample was injected in both runs.