Precise flow control with internal pneumatic micropump for highly sensitive solid-phase extraction liquid electrode plasma

Abstract Liquid electrode plasma (LEP) optical emission spectrometry (OES) is a novel elemental analysis method that utilizes discharged microplasma in a liquid sample as an excitation source to detect metal ions. LEP-OES has been commercialized as a handy device that uses disposable microfluidic chips. To improve the sensitivity, integration of a solid phase extraction (SPE) column into the LEP chip as preconcentrator was proposed with the use of an external syringe pump for fluid actuation. However, poor control of the external pump at low pumping volumes and high back-pressures caused poor analytical performance of the integrated system. In this study, a simply designed internal pneumatic injection pump was redeveloped and employed as a fluid actuator. The internal pump can be easily operated by an automated pneumatic pressure controller and is capable of injecting a reproducible amount of eluent for each measurement cycle of SPE–LEP. Additionally, the pump acted as a valve to stop the backflow caused by the high pressure created by plasma generation. More precise flow control by the internal pump helped improve the precision of the measurements. For data processing, exponentially modified Gaussian model was utilized to describe the elution peaks. The limit of detection for lead (0.4 ng/mL) was 50 times improved in comparison with conventional LEP. The proposed method and data processing model can be used to develop on-chip detection applications for methods that utilize pulsed microplasma sources.