Anal. Chem. 1995,67, 724-728
Affinity Membrane lntroduction Mass Spectrometry Chen Xu, J. S. Patrick, and R. G. Cooks* Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
A new technique, a t y membrane introduction mass spectrometry, is described. In this method, a chemically modified membrane is used to selectively adsorb analytes bearing a particular functional group and concentrate them from solution. Release of the bound analyte results in its transfer across the membrane and allows it to be monitored mass spectrometrically,using, in the present case, a benchtop ion trap instrument. Alkylamine-modified cellulose membranes are used to bind substituted benzaldehydes through imine formation at high pH. Release of the bound aldehyde is achieved by acid hydrolysis of the surface-boundimine. Benzaldehyde is detected with excellent speciscityat 10 ppm in a complex mixture using this method. Using the enrichment capability of the membrane, a full mass spectrum of benzaldehyde can be measured at a concentration of 10 ppb. The behavior of a variety of other aldehydes is also discussed to illustrate the capabilities of the method. Membrane introduction mass spectrometry (MIMS) has seen use in a variety of areas including analysis of biological systems,2J trace environmental and monitoring of reaction kineti c ~ The . ~ strength of MIMS resides in, among other traits, its ability to allow the transfer of volatile and semivolatile compounds from aqueous solution or other matrices to the gas phase with good efficiency. The transfer involves the adsorption of the analyte onto the membrane followed by diffusion across the membrane and into the vacuum, thus providing some degree of enrichment, depending on the membrane chosen. MIMS offers several other desirable qualities including the ability to quantitate some organic compounds at trace concentrations (
