Laser desorption-membrane introduction mass spectrometry

In this paper we describe the first use of laser desorption in conjunction with membrane introduction mass spectrometry (MIMS). In this technique, a low-powered carbon dioxide laser is used to irradiate the low-pressure (vacuum) side of a silicone membrane during a typical MIMS analysis of an aqueous solution. The absorption of laser energy results in direct membrane heating and rapid desorption of permeate molecules. This improves both the sensitivity and response times of MIMS when analyzing compounds having high molecular weight and low volatility. Two simple interfaces are described for performing laser desorption inside and outside the vacuum manifold of a GCQ ion trap mass spectrometer. Together with flow injection (FI) sample introduction, we demonstrate direct on-line monitoring of aqueous solutions of high boiling point (200-530 °C) polynuclear aromatic hydrocarbons such as naphthalene, anthracene, pyrene, benzo[b]fluoranthene, and indeno[123-cd]pyrene.