General rule of thumb—collect all fractions to help troubleshoot and method optimization
Occasionally, one may encounter a ghost peak post extraction regardless of the analytical or detection method.
Possible sources of the mystery peak:
a). Reagents
Reagents and additives may be contaminated. Check reagents.
b). Sample pretreatment
The extra peak can come from the sample pretreatment step. Compare chromatograms of extracted and non-extracted sample
c). Injection solvent
Analytes that are unretained due to high organic injection solvent will appear as extra peaks. Using initial mobile phase condition as injection solvent is recommended
d). Incorrect SPE method
Was the cartridge properly conditioned and equilibrated? Typically, the strongest solvent used in the method should be used to condition the cartridge
Go back to conditioning, loading and washing fractions, was the same peak observed?
e). SPE tube leaching
If reagents or the nature of the sample are too harsh for the SPE polypropylene tube, perhaps a glass tube or Teflon tube should be used instead
f). Degradation/ Side Reaction
Check reactivity and stability of all components in your sample. Degradation can happen if compounds are sensitive to factors such as heat, light, temperature, acids, bases, etc
Sample components may be reacting with each other or reagents/additives involved to take different forms
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