A CRYOTRAP MEMBRANE INTRODUCTION MASS-SPECTROMETRY SYSTEM FOR ANALYSIS OF VOLATILE ORGANIC-COMPOUNDS IN WATER AT THE LOW PARTS-PER-TRILLIONLEVEL

Detection of volatile organic compounds (VOCs) in aqueous solution at low parts-per-trillion (ppt) levels is accomplished using a very simpl e and efficient on-line preconcentration cryotrap membrane introductio n mass spectrometry (CT-MIMS) system, The conventional MIMS probe is m odified so that the membrane interface is placed about 15 cm away from the ion source, A U-shaped trap tube is then inserted between the mem brane interface and the ion source, Cryotrapping is performed with liq uid nitrogen for 15 min, followed by fast heating at similar to 15 deg rees C s(-1), which thermally releases the condensed VOCs almost at on ce into the ion source region of a quadrupole mass spectrometer. By ap plying electron ionization and a selective ion monitoring scan mode, a very sharp and intense peak is obtained. The performance of the CT-MI MS system was compared with that of conventional MIMS, and after reach ing the best conditions for the trapping and heating cycles, an improv ement factor in signal intensity of about 100 was observed for a serie s of VOCs. The extraordinary sensitivity of CT-MIMS system allows VOCs to be detected at very low concentrations, detection limits being typ ically on the order of 10-20 ppt. The results also show excellent line arity and reproducibility fur the system.