Analysis of glycopeptide biomarkers by on-line TiO2 solid-phase extraction capillary electrophoresis-mass spectrometry

In this study is described an on-line titanium dioxide solid-phase extraction capillary electrophoresis-mass spectrometry (TiO2-SPE-CE-MS) method for the analysis of the glycopeptide glycoforms obtained from the tryptic digests of recombinant human erythropoietin (rhEPO). The O-126-glycopeptide of rhEPO was used to optimize the methodology given its importance in quality control of biopharmaceuticals and doping analysis. Several aspects that affect the selective retention and elution, peak efficiency and electrophoretic separation of the O-126 glycoforms were investigated to maximize detection sensitivity while minimizing non-specific retention of peptides. Under the optimized conditions, the microcartridge lifetime was around 10 analyses and repeatability was acceptable (%RSD values of 9-11% and 6-11% for migration times and peak areas, respectively). The method was linear between 0.5 and 50 mg L-1 and 10-50 mg L-1 for O-126 glycoforms containing NeuAc and NeuGc, respectively, and limits of detection (LODs) were up to 100 times lower than by CE-MS. Although optimized for O-glycopeptides, the method proved also successful for preconcentration of N-83-glycopeptides, without compromising the separation between glycopeptide glycoforms with different number of sialic acids. Tryptic digests of other glycoproteins (i.e. human apolipoprotein CIII (APO-C3) and bovine alpha-1-acid glycoprotein (bAGP)) were also analyzed, demonstrating the applicability to glycopeptides with different glycan composition and nature.