环境水中有机污染物检测方案

Detection of Low Levels ofOrganic SpeciesAPPLICATION NOTEHiden Analytical Ltd.， 420 Europa Boulevard， Warrington WA5 7UN， United KingdomTel： +44 (0) 1925 445225 Fax： +44 (0) 1925 416518Email： info@hiden.co.uk Web： HidenAnalytical.com北京办事处电话：：010-68728590/1，51661720；网址： www.Hiden.cn in Seawater Detection of Low Levels ofOrganic Species in Seawater In this particular experiment， the sensitivity ofa Hiden Quadrupole Mass Spectrometer (QMS) to dimethylsulphide wasmeasured. Dimethylsulphide (DMS)- chemical formula CH，SCH，- is a naturally produced trace substance， evolved fromcertain marine microorganisms， suchas apslankton.Detection of fluctuations in the DMS concentration inseawater therefore gives important information about theabundance of these life forms. DMS is a simple chemical. It is volatile and dissolveseasily in aqueous solution. A summary of the mainpeaks of the cracking pattern from the NIST database isseen in Table 1. Mass/amu Intensity /% Ionic Species 62 99.9 CH，SCH， 47 95.4 CHS 45 40.8 CHS 46 36.1 CHS 61 33.3 CH，SCH2 35 32.2 SH 27 20.7 CHCH Table 1： Summary ofcracking pattern for DMS. Research carried out by Philippe D. Tortell of the Dept.of Botany at the University of British Columbia，Canada， has shown that very low levels of detection canbe achieved using a quadrupole mass spectrometer. Toconduct these experiments， a Hiden HPR-40 QMSsystem was used. The system is specifically designed forthe detection1 of volatile species (such asDMS)dissolved in aqueous sample media.Other analysisapplication areas include soil analysis， fermentationcultures and water quality monitoring. The HPR-40 semi-permeable membrane inlet allowsdissolved species to be analysed， whilst preventing thebulk liquid to enter the QMS vacuum chamber. The membrane inlet permeability to volatile organicspecies， compared to non-volatile inorganic species，enhances the systems detection capability for volatileorganic species including DMS. In the University of Columbia experiment， successivedilution was used to reduce the concentration of DMS in thesample. The strongest peak at mass 62 amu was used tomeasure the concentration of DMS. Figure 1： Plot of 62 amu Partial Pressure versus ppbconcentration of DMS in seawater. As can be seen in Figure 1， the linear relationship gives ahigh degree of confidence regarding the detection levels.Further experiments could extend this detection level downto lower partial pressures. The detection limit of thespectrometer is 2 x 10-14Torr. Figure 2 the data points in the parts per billion (ppb) range，illustrate remarkable linearity. Figure 2： Plot of62 amu Partial Pressure versus lowerppb concentration ofDMS in seawater.