Application of 10.6.MU.m CO2 Laser to the Electrospray and Ion Spray LC/MS Interface.

Abstract

A sudy on the application of infrared (IR) CO2 laser (10.6 μm) to the LC/MS interface was made. When the IR laser was irradiated on the tip of the quartz capillary tube with the sample flow rate of a few tens μl/min, intense alkaline ions (Na+ and K+) and O2-ion were observed. However, the ion signals originating from thermally labile samples could not be detected due to the thermal degradation. The tetraalkylammonium ions could be detected when the stainless steel capillary was used. Irradiation of IR laser near the tip of the Taylor cone of the electrospray promoted the efficient vaporization of charged liquid droplets resulted in the drastic increase of the sample ion signal. When SF6-containing N2 was used for the ion spray as a nebulizer gas, a drastic increase of the amino acid ion signals was observed. This is due to the enhanced evaporation of the charged liquid droplets caused by the efficient absorption of 10.6 μm IR laser by SF6 gas. When IR laser was irradiated on the electrosprayed charged liquid droplets for 10-5 M tubocurarine chloride (M) solution in isopropanol/aqueous NH3 (29%) solution, the intensity of the singly charged ion (M-HCl-Cl)+ increased but that of doubly charged ion (M-2Cl)2+ decreased. This may be due to the enhanced surface evaporation of the charged liquid droplets caused by the efficient absorption of IR laser by ammonia solution. The surface evaporation results in the increase of ions with larger surface activities but the ions with smaller surface activities are rather insensitive to the surface evaporation because they are mainly solvated not near the surface but inside the liquid droplets.