Improved hydrostatic pressure sample injection by tilting the microchip towards the disposable miniaturized CE device

Abstract

A simple method of hydrostatic pressure sample injection towards a disposable microchip CE device was developed. The liquid level in the sample reservoir was higher than that in the sample waste reservoir (SWR) by tilting microchip and hydrostatic pressure was generated, the sample was driven to pass through injection channel into SWR. After sample loading, the microchip was levelled for separation under applied high separation voltage. Effects of tilted angle, initial liquid height and injection duration on electrophoresis were investigated. With enough injection duration, the injection result was little affected by tilted angle and initial liquid heights in the reservoirs. Injection duration for obtaining a stable sample plug was mainly dependent on the tilted angle rather than the initial height of liquid. Experimental results were consistent with theoretical prediction. Fluorescence observation and electrochemical detection of dopamine and catechol were employed to verify the feasibility of tilted microchip hydrostatic pressure injection. Good reproducibility of this injection method was obtained. Because the instrumentation was simplified and no additional hardware was needed in this technology, the proposed method would be potentially useful in disposable devices.

Instrumentation design for hydrodynamic sample injection in microchip electrophoresis: A review

“…WE is the working electrode used in the electrochemical detection. Images (A and B) are reprinted from with permission.…”

Pump‐free and low‐cost negative pressure sampling device for rapid sample loading in MCE

“…Up to now, electrokinetically pinched injection [4][5], which allows injecting samples in minute quantities that is geometrically defined by the intersection of a cross-shaped [6][7] or a double-T shaped [8] fluidic channel, is the most commonly used method. Two of the main limitations of electrokinetic injection are its strong dependency on surface properties of channel walls and the bias effect towards different species [9]. To avoid biased injection, sample loading by pressure injection methods, which are insensitive to channel surface and sample properties, were developed [9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…Two of the main limitations of electrokinetic injection are its strong dependency on surface properties of channel walls and the bias effect towards different species [9]. To avoid biased injection, sample loading by pressure injection methods, which are insensitive to channel surface and sample properties, were developed [9][10][11][12][13][14][15][16][17][18][19][20][21]. Bai et al applied six-port valve and three syringe pumps to provide pressure for pinched nanoliter volume injection [10].…”

“…To avoid using pump and additional hardware, Gai et al proposed the sample injection using hydrostatic pressure in conjunction with electrokinetic force [19] and Luo et al developed this method to realize variable sample plug volume [20]. Wang et al improved hydrostatic pressure sample injection by tilting the microchip [9]. Yang et al used a water-filled U-tube manometer to generate a negative pressure to pull the sample from the sample reservoir (S) into SW [21].…”

“…However, the sampling time was relative long, typically 30-60 s, owing to the small driving force from the difference of the liquid height in different reservoirs. Besides, the operation was cumbersome [9,21].…”