Experimental Upgrades of Membrane Introduction Mass Spectrometry for Water and Air Analysis

Abstract

Some improvements to the membrane introduction mass spectrometry (MIMS) technique, resulting in low-ppt detection limits for volatile organohalogen compounds (CX) in water (namely, chloroform, bromoform, bromodichloromethane, chlorodibromomethane, tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and carbon tetrachloride) and low-microgram per cubic meter detection limits for benzene, toluene, ethylbenzene, and xylenes (BTEX) in gaseous samples, are shown. A static MIMS configuration was compared to a dynamic one, the former requiring longer time to obtain the analytical response. A cryotrapping preconcentration step is introduced and linearity of response, mixture effects, and detection limits are presented. The instrumental setup consists of a hollow fiber silicone membrane, a water or air container, a cryofocusing trap based on Tenax adsorbent, a Peltier cell, and a Varian ion trap benchtop mass spectrometer is described. This instrumental setup, which we named membrane extraction trap focusing mass spectrometry, allowed the detection of CX in water at a concentration as low as 8 ppt and of benzene in air at 0.1 μg/m3. The whole assembly shows great potential for on-site routine monitoring of drinking water resources and urban and indoor air under current EU and Italian regulations.