On-chip integration of neutral ionophore-based ion pair extraction reaction

Integration of a neutral ionophore-based ion pair extraction reaction onto a glass microchip was performed. Since the Liquid microspace provides a sho rt molecular diffusion distance and a large specific interfacial area of th e liquid-liquid interface, novel attractive analytical features arise such as extremely fast ion sensing and ultrasmall reagent solution volume. In co ntrast to the slow response time of a standard ion optode, in which the res ponse time is basically governed by slow diffusion of ionic species in the viscous polymer membrane, that of the on-chip ion-sensing system is clearly faster due to the short molecular diffusion distance and low viscosity of organic solution. In this case, the organic solution containing a neutral i onophore and a lipophilic pH indicator dye and the aqueous solution contain ing sample ion were independently introduced into microchannel to form an o rganic-aqueous interface. Then determination of the ion was performed by th ermal lens microscopy at the downstream of the organic phase under continuo us-now conditions. The response time and minimum required reagent solution volume of the on-chip ion-sensing system are about 8 s and 125 nL, respecti vely, indicating the advantages of using the liquid microspace. Other advan tages of the on-chip ion pair extraction system arising from using the liqu id microspace and microfluidic system are also discussed in detail.