More on IS response variations [Regulatives / Guidelines]

posted by ElMaestro  – Belgium?, 2019-11-12 16:25  – Posting: # 20793
Views: 1,031

Ahem,

» » » […] "perhaps it is the ion source blah"
» »
» » If a stable isotope labeled internal standard is used, that’s the only reasonable explanation for me.
»
» Well, it could also be a wrong dilution during the preparation of a new working solution, a variable recovery...

it could be a ton of things. Matrix effect, variation stemming from different sources of plasma ("But is passed the selectivity experiments blah blah"). Even solar flares can under the right circumstances be detected by LC-MS/MS.

Different stocks, different storages, different equipment, pipetting errors, robot programming, different this, different that. And you get some info by also looking at the slope of the cal. curve in those cases.
But still, let us discuss how to establish the presence of the phenomenon before addressing causes? Let us say the average IS of cals+QCs in one run is 8x the average IS of cals+QC's in another run and all passing the usual criteria.
Would you be concerned?
Yes? Why?
No? Why not?
Not enough info? Which questions would you ask? (I would e.g. consider matrix sources used for QC's+cals, pipetting, volumes, station, method settings, columns, possibly grid anomalies if I can get such info, but all that will usually leave a blank)

I could be wrong, but...
Best regards,
ElMaestro

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