On-line solid-phase extraction to enhance sensitivity in peptide biomarker analysis by microseparation techniques coupled to mass spectrometry: Capillary liquid chromatography versus capillary electrophoresis

In this study, on-line solid-phase extraction capillary liquid chromatography-mass spectrometry (SPE-CapLC-MS) and electrophoresis-mass (SPE-CE-MS) were compared for the analysis of opioid peptide biomarkers dynorphin A (1–7) (DynA), endomorphin 1 (End 1), methionine-enkephalin (Met). First, a (CapLC-MS) method was established, which allowed limits detection (LODs) 0.5 μg/mL Dyn Met, 0.1 End 1. Then, column switching setup operated by 2-position/6-port micro-valve with C18 enrichment assembled SPE-CapLC-MS. Under optimized conditions, LODs three peptides lowered up to 1000-fold CapLC-MS, until detecting ng/mL concentrations. Repeatability (<0.2 % <11 RSD retention times peak areas, respectively), linearity (0.5–100 ng/mL), durability (20 runs) appropriate, applied analyze human plasma samples. Finally, established SPE-CapLC-MS valve-free C18-SPE-CE-MS previously described our group these peptides, using same mass spectrometer. Both methods presented an evident difference regarding need valve operation high preconcentration factors quite similar (until SPE-CaLC-MS SPE-CE-MS, respectively). Some other distinctions related instrumental set-up, procedure performance also disclosed discussed in detail.