A polymeric microfluidic chip made of Zeonor 1020 was fabricated using conventional embossing techniques to perform capillary electrophoresis for selected ion monitoring and selected reaction monitoring mass spectrometric detection of small molecules. A silicon master was microfabricated using photolithographic and dry etching processes. The microfluidic channel was embossed in the plastic from a silicon master. The embossed chip was thermally bonded with a Zeonor 1020 cover to form an enclosed channel. This channel (60-microm width, 20-microm depth, 2.0- and 3.5-cm length) provided capillary electrophoresis (CE) separation of polar small molecules without surface treatment of the polymer. A microsprayer coupled via a microliquid junction provided direct electrospray mass spectrometric detection of CE-separated components. An electric field of 0.5-2 kV/cm applied between the microsprayer and a separation buffer reservoir produced a separation of carnitine, acylcarnitine, and butylcarnitine with separation efficiencies ranging from 1,650 to 18,000 plates. Injection quantities of 0.2 nmol of these compounds produced a separation of the targeted polar small molecules without surface treatment of the polymer-abundant ion current signals and baseline separation of these compounds in less than 10 s. These results suggest the feasibility of polymeric chip-based devices for ion spray CE/MS applications.
Sodium-ion capacitors (NICs) are considered an important candidate for large-scale energy storage in virtue of their superior energy–power properties, as well as availability of rich Na+ reserves. To fabricate high-performance NIC electrode material, a hydrothermal method was proposed to synthesize sulfur-doped reduced graphene oxide (SG), which exhibited unique layered structures and showed excellent electrochemical properties with 116 F/g capacitance at 1 A/g as the cathode of NICs from 1.6 V to 4.2 V. At the power–energy density over 5000 W/kg, the SG demonstrated over 100 Wh/kg energy density after 3500 cycles, which indicated its efficient durability and superior power–energy properties. The addition of a sulfur source in the hydrothermal process led to the higher specific surface area and more abundant micropores of SG when compared with those of reduced graphene oxide (rGO), thus SG exhibited much better electrochemical properties than those shown by rGO. Partially substituting surface oxygen-containing groups of rGO with sulfur-containing groups also facilitated the enhanced sodium-ion storage ability of SG by introducing sufficient pseudocapacitance.
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