Using Temperature to Improve the Limits of Detection in ?on-line? SPE-CE Systems

MARCOS TASCÓN; LEONARDO G. GAGLIARDI; FERNANDO J. BENAVENTE MORENO

Florianópolis

Congreso; COLACRO XIV - Congreso Latinoamericano de Cromatografia y Técnicas Relacionadas; 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 improve the poor limits of detection (LOD) of CE. Concentration methods based on solid phase extraction on-line have been carried out with excellent results [1,2]. However, the use of temperature to further improve SPE-CE systems has not been investigated. This approach can be explored easily with commercial instruments. Since the microcartridge SPE is placed near the inlet end of the separation capillary but within the cassette is possible to scan the temperatures of the loading and elution using just the internal temperature control of the cassette [1.2]. However, the use of localized thermostatting systems provide better results and allow to study a range of temperatures much wider than the standard instrument. The aim of this work was to investigate the influence of temperature on the SPE-CE using microcartridges packed with commercial C18 stationary phases and opioid peptides as model compounds. Opioid peptides are a group of neuropeptides of biomedical interest, which are usually present in biological fluids at extremely low concentrations, typically subnanomolar. First, we evaluated the thermal stability of these analytes to 95 ° C. Secondly, we studied the effect of changing temperature from 25 to 60° C, on the sample loading, on elution and on the separation, using the standard thermostatting system of the commercial instrument. Subsequently, we designed a micro-water bath to control the microcartridge temperature at any value between 0 and 100° C. We found several incompatibilities of the materials and assemblies of microcartridges with the high temperatures. After many trials and as a result of the introduction of several changes we achieved a robust system which was used with excellent results. In order to normalize the amounts introduced hydrodynamically at the different temperatures into the SPE-CE column some corrections were made taking into account the change in viscosity with temperature. The increase of temperature causes an unexpected variety of effects in the different analytes. In some of them considerable variations of retention with temperature are observed. In most of the cases to increase loading temperatures improve significantly the LOD. This demonstrates the potential of the temperature to further improve sensitivity in SPE-EC where the analytes are thermally stable.