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Generation of picoliter droplets of liquid for electrospray ionization with piezoelectric inkjet
Authors:Chen Luo  Yuan Ma  Haifang Li  Fengming Chen  Katsumi Uchiyama  Jin‐Ming Lin
Institution:1. Beijing Key Laboratory of Microanalytical Methods and Instrumentation, Department of Chemistry, Tsinghua University, , Beijing, 100084 China;2. Department of Applied Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, , Tokyo, 192‐0397 Japan
Abstract:We report the association of inkjet and electrospray ionization MS to detect picoliter droplet, where the liquid volume and its position onto the tip can be precisely controlled to form ultrafine droplets for successive ionization of the analyte. Single rectangle pulse was applied to piezoelectric device on inkjet microchip for the ejection of each picoliter droplet, and it was controlled by a computer. The voltage and width of driving pulse for the inkjet were optimized to make reproducible ejection of the solvent with low viscosity. The volume of each droplet was about 600 pl, and a trigger of 10 droplets was selected as the best inlet mode taking relative standard derivation of the droplets into consideration. The target substrate used with high voltage to form ionization was graphite, after several attempts with some materials. High‐speed camera was used to capture the breaking‐up process of a droplet. The distance between the inkjet nozzle and the tip was set at 2 cm to avoid short circuit. The influences on the mass intensity of the diameter of the tip, the volume and the concentration of the sample were examined. The tip with a small diameter performed greater intensity, and the limit of detection decreased, whereas the small volume of liquid played high ionization efficiency. Linear regression in the range between 1 and 200 ppm for caffeine was conducted, where internal standard theobromine was used. Some real samples were also detected with the instrument. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords:picoliter droplet  inkjet  ionization  MS  piezoelectric device
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