Since the inner diameter of the funnel-shape vessel gradually reduced from 3 mm to 0.4 mm, the end of the sampling capillary of the pneumatic nebulizer of the FAA spectrometer could be simply introduced into the lower part of the vessel. The liquid content of the plastic sampling vessel was instantly sucked out by the PTFE capillary of the nebulizer when it was immersed into the vessel. The length of the capillary was reduced to 10 cm to minimize the dispersion of the liquid sample on the surface of the capillary between the microchip and the nebulizer (Fig. 1e).