Temperature-mediated on-line solid-phase extraction capillary electrophoresis (SPE-CE) for analysis of opioid peptides

MARCOS TASCÓN; LEONARDO G. GAGLIARDI; FERNANDO J. BENAVENTE MORENO; JOSÉ BARBOSA; VICTORIA SANZ-NEBOT

Ginebra

Simposio; 27th International Symposium on MicroScale BioSeparations and Analyses (MSB2012); 2012

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm; direction: ltr; color: #000000; text-align: left; widows: 2; orphans: 2 } P.western { font-family: "Times New Roman", serif; font-size: 12pt; so-language: en-GB } P.cjk { font-family: "Times New Roman", serif; font-size: 12pt; so-language: zh-CN } P.ctl { font-family: "Times New Roman", serif; font-size: 12pt; so-language: ar-SA } --> There have been many attempts to overcome the poor concentration limit of detection (LOD) in CE without using off-line approaches. Developments aimed at improving ultraviolet, electrochemical, fluorescence, chemiluminiscent and mass spectrometry detection, have had limited success. Alternatively, several electrophoretic or chromatographic approaches for on-line preconcentration based on stacking or solid-phase extraction have been extensively investigated with excellent results [1,2]. However, only a few researchers have realized about the potential of manipulating temperature for such purposes, in combination or not with the previous strategies [3]. In SPE, temperature is an optimization parameter which has often been overlooked during method development, despite it is well-known the influence on solubility and chromatographic efficiency, selectivity and mobile phase viscosity [4]. To the best of our knowledge no authors have investigated temperature in combination with SPE-CE, despite this approach can be easily explored to a certain extent with commercial instruments. Loading or elution temperatures can be easily selected because the SPE microcartridge is usually placed near the inlet of the separation capillary inside the cassette with temperature control [1,2]. The aim of this work was to investigate the influence of temperature in SPE-CE using lab-made microcartridges with several commercial chromatographic sorbents and opioid peptides as model compounds. Opiod peptides are a group of neuropeptides of biomedical interest generally present in biological fluids at extremely low concentrations, typically subnanomolar concentrations. First, we evaluated peptide thermal stability until 95 ºC. Second, we investigated sample loading, elution and separation between 25 and 60 ºC, using the air thermostatization system provided with the commercial instrument. Later, we designed a lab-made set-up to assist specifically microcartridge thermostatization until 90 ºC using an external water bath. In order to make results comparable, it is worth mentioning that the volumes hydrodynamically introduced inside the SPE-CE column were corrected taking into account the change of viscosity with temperature. Under optimum conditions, analysis time was shortened at higher temperature because of the increase in BGE conductivity promoted by the decrease in viscosity. Furthermore, LODs were significantly improved for some of the studied peptides indicating the potential of temperature to further enhance sensitivity in SPE-CE when the analytes are thermally stable.