Miniature and fully portable gradient capillary liquid chromatograph

A robust, portable and miniature battery powered gradient capillary liquid chromatograph (total weight ~2.7 kg, without battery ~2.0 kg), with integrated microfluidic injection, column heating and high sensitivity low-UV absorbance detection is presented. The portable capillary chromatograph, was applied with a packed reversed-phase capillary column (100 mm x 300 μm I.D., 5 μm ODS), housed within an integrated capillary column heater controlled by a proportional-integral-derivative (PID) chip module. The system delivered retention time and peak area relative standard deviation in isocratic mode of <0.7% (n = 10) and <3.3% (n = 10), respectively, and <0.1% (n = 10) and <2.3% (n = 10) respectively, for gradient elution mode. Detection was based upon a 255 nm light-emitting diode (LED) using one of two commercial capillary flow-cell options, namely a high sensitivity 12 nL Agilent capillary z-cell (HSDC) and a 45 nL Thermo Fisher Scientific UZ-View™ flow cell (UZFC). The HSDC, housed within a 3D printed detector arrangement, gave an effective pathlength of 1.01 mm (84% of nominal pathlength) and stray light of only 0.2%. Limits of detection for four test small molecule pharmaceuticals ranged from 65 to 101 μg L⁻¹ based upon a 316 nL injection volume, with separation efficiencies of between 18,000 and 29,700 N m⁻¹, with sub-4 min run times. The portable capillary LC system was successfully coupled to a small footprint portable mass spectrometer (Microsaic 4500 MiD) to demonstrate compatibility and ‘point-of-need’ miniaturised LC-MS capability.