This question is very valuable because while working in a QC environment you don't have certain privileges unlike R & D labs. Everything there is a one shot process and if anything doesn't come along or doesn't go as expected whether its system suitability or RT shifts observed in your standards, there is immediate need to raise incidents or deviations. And adding on, if the buffer system has salts its even more challenging to bring about the required criteria like system suitability to pass at first attempt. So I need some expert guidance and ideas regarding this.
Everything depends on how Your analytical methods and procedures in Your QC lab are written. It is well-known fact that sometimes first injection of samples/standard does not chromatography as it should. This applies especially in gradient methods, where the retention of a peak is related to the time of gradient stabilization of the previous injection.
Additionally, if the System Suitability Test (SST) have requirement of retention time +/- of peak such methods should be changed in order to QC not having such problem as you describe. The SST for assay mostly should consider good peak shape (asymmetry and/or theoretical plates) and if it's necessary resolution from any impurities.
In my opinion, such problems should be considered when the method is developed and validated. It is a normal thing that columns deteriorate, buffer composition will have some ionic strength deviance, different HPLC systems having different dwell volume, a little different solvent mixer. Analytical methods should consider all of those possible changes in order to ease QC.
RT shift occurs for many reasons:
1. presence of bubble in channels
2. presence of volatile substances in mobile phase
3. when components in mobile phase are not mixed well
4. presence of bubble in sample/standard vial
5. insufficient washing solvent (like IPA)
6. using 100% methanol/acetonitril in any channel (very volatile)
You have to be very careful about all these things before running HPLC machines. When you use any salt ensure that it has been uniformly mixed, sonicated and you have to mix it mechanically during sonication. Ensure that there is no bubble in the channel. purge each channel after introducing a new liquid. saturate the column with care. you will have to use buffer (of salt) and acetonitril/methanol in gradient sometimes. seal the organic containing jar's openings with aerotape.
Best of luck!
Thanks Adam Zmyslowski and thanks F.s. Shanta for the guidance and insights.
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