DETECTION OF DMS USING HAND-HELD IMS - B & S Analytik GmbH

DETECTION OF DMS USING HAND-HELD IMSJohannes Flachowsky, Michaela Brodacki, Joachim StachABSTRACTThe paper describes an analyticalmethod for on-site detection of DMS (DiMethyl Sulfate) using ion mobilityspectrometry (IMS). The ion mobility spectraof DMS recorded in the negative mode show asingle peak with a reduced ion mobilityconstant k 0 = 1.96 cm 2 /Vs. Using this signal,it is possible to measure DMS in the range of 5to 100 ppb/m 3 . The detection limit determinedunder laboratory conditions is 3ppb.Interference of matrix compounds likecoolants have been detected but can bemanaged using simple sample preparationprocedures.INTRODUCTIONDMS is an important component forsynthesis of chemical compounds. It isproduced in large quantities. Due to the hightoxicity [1], the production of DMS ischaracterized by high security precautions.The tolerable values for the concentration ofDMS are 0.1 mg/m 3 (20 ppb v ) in air and 0.2mg/m 3 (40 ppb v ) in the working placeatmosphere.The prescribed detection method forDMS according to the German: BGI 505-7 aretime consuming. The method is based onadsorption of DMS on TENAX followed byelution of the adsorbed DMS with methylacetate. The obtained solution is analyzedusing gas chromatography (GC) or GC/MS.The achieved absolute detection limits are inthe range of 3 ng DMS. The analysis time isabout 15 minutes.During the production process of DMSshort term variations of the DMSconcentration might occur which can exceedFigure 1: Series of ion mobility spectra of DMS (c= 19,6ppb) recorded in the negativeion modeReceived for review April 5, 2002, Accepted July 12, 2002

40 - DETECTION OF DMS USING HAND-HELD IMSFigure 2: Trend of the DMS peak with k 0 = 1.96 cm 2 /Vs demonstrating fast response andrecovery times of DMS detectionthe above given concentration limits. Thesevariations cannot be detected with theprescribed method due to required analysistime. Especially for this application on-lineanalysis methods like IMS [2,3] are requiredfor detection of DMS. In addition hand-heldIMS does also support the safe handling ofDMS in facilities, storage tanks etc.RESULTSDMS forms a single peak in thenegative mode with a reduced ion mobility ofk0 = 1.96 cm 2 /Vs. The detection is possiblewith short response and recovery times. Atypical series of ion mobility spectra is shownin Fig. 1. The trend for the DMS peak with k0= 1.96 cm 2 /Vs is displayed in Fig. 2. On-linedetection is possible with a very highsensitivity. The calibration curve is displayedin Fig. 3. The measured detection limit is 3ppb. The linear range of the calibration curveis between 3 and 40 ppb which fit therequired detection range for monitoring ofproduction facilities.The use of hand-held for detection ofDMS in production facilities is simple andsafe. A very low number of interferingsubstances has been reported so far.However, in one particular case very highconcentrations of DMS were detected inunexpected parts of a production facilitywhere the risk for DMS contamination iscomparatively low. The signals showed a verylong response and recovery time contrary totypical DMS detection. A more detailedinspection showed that the strong DMSsignals were caused by ethylene glycol. Acompound used as coolant. The detectedconcentration was about 2000 times higherthan DMS concentration. Considering theproperties of ethylene glycol, especially thehigh solubility in water, this interference canbe prevented using special filter which can beinstalled in front of the gas inlet of the IMS.References[1] Merk Chemie Datenbank 2002, http://www.chemdat.de[2] Eiceman, G.A.; Karpaz, Z.; Ion MobilitySpectrometry, CRC Press, Boca Raton, 1994.[3] Stach, J.; Analytiker Taschenbuch, Vol. 16,1997, 119.Copyright © 2003 by International Society for Ion Mobility Spectrometry