Abstract
In this study, polydimethylsiloxane (PDMS)-coated capillary columns (TRB-5 and TRB-35), both unmodified and functionalized with single-wall carbon nanotubes (SWCNTs) or multiwall carbon nanotubes (MWCNTs), have been tested and compared for the extraction of amphetamine (AMP), methamphetamine (MET) and ephedrine (EPE) by in-tube solid-phase microextraction (IT-SPME). Prior to their extraction, the analytes were derivatized with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC). For separation and detection capillary chromatography with fluorimetric detection has been used. The presence of carbon nanotubes in the extractive coatings enhanced the extraction efficiencies and also significantly improved the chromatographic profiles, thus resulting in a reliable option for the analysis of these drugs. As an example of application, a new method is proposed for the analysis of the tested amphetamines in oral fluid using a TRB-35 capillary column functionalized with MWCNTs. The proposed conditions provided suitable selectivity and reproducibility (CV ≤ 6%, n = 3) at low µg/mL levels, and limits of detection of 0.5–0.8 µg/mL.
Highlights
Among the novel microextraction techniques developed in the last decades, in-tube solid-phase microextraction (IT-SPME) has emerged as one of the most attractive options, as demonstrated by the increasing number of publications that use it for the analysis of a variety of analytes and matrices [1].IT-SPME typically uses a polymeric-coated capillary column coupled to a liquid chromatograph.The target compounds can be extracted by repeated draw/injection cycles of the samples using a programmable sample injector until the analytes reach partition equilibrium between the coating of the capillary and the sample
When IT-SPME is combined on-line with capillary liquid chromatography, peak widths of the analytes are significantly higher than those typically achieved by conventional capillary chromatography, which is due to the inclusion of the extractive capillary in the chromatography system
When an IT-SPME device is added to the chromatographic system, a reduction in the mobile-phase flow rate would increase the time of residence of the analytes in the extractive capillary causing extra peak broadening [17]
Summary
Among the novel microextraction techniques developed in the last decades, in-tube solid-phase microextraction (IT-SPME) has emerged as one of the most attractive options, as demonstrated by the increasing number of publications that use it for the analysis of a variety of analytes and matrices [1]. The extractive capillary can be used as the loop of the injector valve (in-valve IT-SPME), and a volume of sample as large as necessary (up to several mL) is passed through the capillary until the amount of analytes extracted is sufficient to reach the required analytical responses The former option has been extensively used for the analysis of drugs and biomarkers in biological fluids, whereas the in-valve. Enhancing the extraction capability of the capillary coating may be the key factor to extend the applicability of in-valve IT-SPME to those analytical problems in which the volume of sample is limited. Different PDMS-based extractive capillaries both unmodified and modified with CNTs have been investigated As indicated above, these coatings have been previously applied to the extraction of organic pollutants from water samples [10,11].
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