I'm doing a targeted metabolite analysis using LCMS. I did a LCMS assay once using a set of serum samples processed for LCMS. However I wanted to repeat the LCMS run, using the same set of samples to optimize the protocol used for LCMS. The re-run was done using the initial processed samples which were stored in -80'C for about 2 months. The precision of the data of the repeated analysis was low and I didn't detect peaks for some of the metabolites which were detected in the initial run. Could you please let me know whether processed samples once used for LCMS couldn't be used again and if so, what is the reason for that?
Yes.
You can re-run the the previous samples again on LC-MS system.
Although, you mentioned that, samples were stored in suitable conditions, but it is not sure the metabolite/s you want to check in your sample are still in same concentration or form. It may be or may not be detectable depending upon various conditions after 2 months of storage.
But, you are free to go for again reuse those samples for run again in LC-MS system.
Before running, Check the samples properly, if there is any precipitation or any particulate matter, that may cause problem to system e.g. blockage in lines, overpressure etc.
Samples must be clear and filtered proper with syringe filter.
Check the protocol first by running a standard solution of targeted metabolite of interest.
If standard peak response and resolution is good enough but you are unable to find or detect the metabolite in samples, there may be chances of problem in sample degradation OR processing.
Periodic analysis of the sample can establish the stability of your sample. Most likely, your sample may have degraded.
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