Pump- and Valve-Free Flow Injection Capillary Liquid Electrode Discharge Optical Emission Spectrometry Coupled to a Droplet Array Platform.

A miniature (2.5 cm length × 2.0 cm width × 1.0 cm height), low power (<10 W), and capillary liquid electrode microplasma optical emission spectrometer was developed for rapid determination of metallic species in aqueous solutions. The sample solution can be automatically introduced into the source without a pump owing to the inherent capillary attraction and the force arising from the solution vaporization induced by microplasma. A droplet array was used as a sampling platform to realize flow injection without using any valve and pump, significantly increasing throughput to 90 samples h-1. Sample volume is controlled through the sampling time and reduced to the nanoliter level. With a sampling time of 10 s (equal to 600 nL), detection limits of 30 μg L-1 (18 pg) and 75 μg L-1 (45 pg) were obtained for Cd and Hg, respectively, comparable to those reported for liquid electrode microplasma optical emission spectrometry. However, sample consumption is reduced more than 100-fold, making the proposed technique more suitable for the analysis of elements such as Cd, Hg, Li, Na, and K when sample volumes may be limited. The utility of this system was demonstrated by the determination of Cd and Hg in blood, real water samples, and Certified Reference Materials (rice powder, GBW07601a, and lobster hepatopancreas, TORT-3).