We investigate the effect of chip tip-to-counter electrode spacing (gap), channel-size aspect ratio, onset voltage on electrospray ionization (ESI) performance of embossed polymer microfluidic chips. Planar polymer substrates were hot embossed using an electroformed tool and a laser machined tool. The embossed microchips were tested for successful ESI demonstration with minimum sample consumption and high throughput. Factors influencing the stability of electrospray were analyzed by a series of experiments. Theoretically and experimentally, it was observed that the distance of the microchannel tip to the counter electrode directly relates to the onset voltage applied. Furthermore, the overall pattern observed is the decrease in Taylor cone size with a decrease in channel dimensions. The total ion current was analyzed as a function of time and onset voltage at various gaps. Five electrospray modes, namely, drop mode, pulse mode, Taylor-cone jet mode, multijet mode, and oscillating jet mode recorded at the open channel tips were identified and the electrospray cycle investigated. These results are in good accordance with theory, and comparisons are drawn with the findings of other researchers.
The aim of this project was to develop high performance polymer microfluidic chips with reduced complexity for
Electrospray Ionization Mass Spectrometry (ESI-MS) analysis. This paper presents the fabrication and testing of
developed hot embossed open channel polymer microfluidic chips for ESI-MS. Hot embossing was done using a laser
machined steel tool and an electroformed nickel tool on polystyrene (PS) and polycarbonate (PC) substrates. Stable
electrosprays were generated at microchannel exits of replicated microchips without cover using a high voltage
difference between a positive stainless steel electrode in the reservoir and a negative aluminum plate. Electrospray
parameters such as; nozzle tip distance from counter electrode, ESI onset potential and duration were investigated. For
open channel systems, the results show that the electric field for stable ES directly relates to the distance between the
channel tip and counter electrode, onset potential applied and to the flow velocity of the test solution in the
microchannel. Fluid is delivered as a result of electroosmosis due to an applied electric field and capillary action,
thereby eliminating the need for external pressure devices. From experimental results, for an open-channel of 100μm
width, 100μm depth, length 12.5mm attached to an open reservoir of diameter 2 mm, the optimum distance between the
channel exit tip and counter electrode is 1.2 mm for initiation of electrospray at voltage of ~2000 volts. The laser
machined steel tool was found to be more durable than the nickel tool for PS/PC microstructure fabrication.
In this paper, we report on the design, fabrication, and testing of a polymer micro fluidic chip for Electrospray Ionization Mass Spectrometry (ESI-MS). A disposable plastic chip is designed to be fabricated using the hot-embossing process on polystyrene (PS) and polycarbonate (PC) substrates. The chip has an open reservoir, which is connected to an open channel that runs to the tip of the chip. A high voltage circuit is required to form the electrospray at the tip using methanol/water solution with an electrode wire in the reservoir. We have tried to minimize sources of impurities entering the microchannel, and hence, the MS, by careful selection of the fabrication process and electrode and use of open channel. The hot-embossing process is modeled using ANSYS to design the tool and predict the channel and reservoir shape and deformation. The simulation results provide an insight into the hot embossing process. Several samples are fabricated and tested, and the electrospray experimental results are reported. Laser machining and electroforming processes were investigated for fabricating the hot-embossing tool, and the results are reported.
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