Transient isotachophoresis in on-line solid phase extraction capillary electrophoresis time-of-flight-mass spectrometry for peptide analysis in human plasma

In this study, we evaluated the combination of transient isotachophoresis with on-line solid-phase extraction capillary electrophoresis time-of-flight mass spectrometry (SPE-tITP-CE-TOF-MS) to improve sensitivity of peptide analysis, using several opioid peptides as model compounds. First, standard solutions were analyzed in order to establish the tITP-CE methodology using UV and TOF-MS detection. The volume and composition of the leading and terminating electrolytes (i.e. LE and TE) for an efficient tITP were investigated to obtain optimum detection sensitivity and electrophoretic separation. In the best cases, LODs in tITP-CE-TOF-MS were tenfold better than those obtained in CE-TOF-MS (i.e. 5 versus 50 ng/mL). Afterwards, the tITP-CE-TOF-MS methodology was adapted to perform SPE-tITP-CE-TOF-MS. Repeatability, linearity and LODs were investigated and compared to the values obtained by SPE-CE-TOF-MS. Furthermore, human plasma samples fortified with the opioid peptides were analyzed in order to show the potential of SPE-tITP-CE-TOF-MS for peptide analysis in biological fluids. The LODs attained in standard solutions and plasma samples for some of the studied peptides (i.e. 0.01 and 0.1 ng/mL, respectively) were tenfold better than those obtained in SPE-CE-TOF-MS, proving the enhanced sensitivity that could be achieved when both on-line preconcentration approaches were combined together.