For the first time, a multi-lumen capillary (MLC) (126 parallel channels of 4.2 µm i.d) has been modified to produce a C18-functionalised silica porous layer open tubular (PLOT) capillary column for both on-capillary preconcentration and separation. The modified multi-lumen capillary used in this dual mode provided significant advantages over typical nano/capillary-LC–MS systems, in that it facilitated both higher sample loading capacity, the use of elevated flow rates, and simplified equipment requirements. Following modification, 100% of the channels displayed a homogenous porous silica layer, 257 ± 36 nm thick. The PLOT-MLC was first evaluated for on-capillary solid-phase extraction. Extraction of caffeine, ofloxacin, atrazine, and diuron was carried out offline using an 8-cm-long PLOT-MLC, with quantification achieved using HPLC coupled to a quadrupole-time of flight (QTOF) mass spectrometer. The results confirmed reversed-phase selectivity and average recoveries obtained were around 70%. Subsequently, a 65-cm-long PLOT-MLC was evaluated as a separator column using a capillary liquid chromatography (Cap-LC) system equipped with a nano-injector and coupled to the mass spectrometer. The short PLOT-MLC provided a baseline separation in isocratic mode [water:acetonitrile (each with 0.1% formic acid) = 70:30, v/v] of ofloxacin, atrazine, and diuron. Finally, direct coupling of the PLOT-MLC with the QTOF via a capillary electrosprayer facilitated the simultaneous use of the modified capillary as a solid-phase concentrator, separator column (carrying out concentration-focusing-separation on the PLOT-MLC) and electrospray emitter. This configuration greatly simplifies the traditional capillary-LC–MS equipment requirements, via the removal of all connectors and additional capillary between injector and MS inlet, and is demonstrated herein with large volume sample loading and step-gradient elution/separation with sensitive MS detection.
Liquid chromatography Mass spectrometry Multi-lumen capillary C18-funtionalised fused silica Porous layer open tubular columns
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The authors wish to acknowledge the Australian Research Council for funding (Grant IC140100022). We would also like to acknowledge the help of Christopher Broinowski, Dr. Sandrin T. Feig, and Dr. Karsten Goemann of the Central Science Laboratory, University of Tasmania, and Petr Smejkal from ACROSS, for the provision of technical support.
Compliance with Ethical Standards
Conflict of interest
The authors declare no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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1.Australian Centre for Research on Separation Science (ACROSS), and ARC Training Centre for Portable Analytical Separation Technologies (ASTech), School of Natural SciencesUniversity of TasmaniaHobartAustralia