Working Report 2006-41 Method Development of Gas Analysis with Mass Spectrometer Timo Kröger Nina Paaso October 2006 POSIVA OY FI-27160 OLKILUOTO, FINLAND Tel +358-2-8372 31 Fax +358-2-8372 3709 Working Report 2006-41 Method Development of Gas Analysis with Mass Spectrometer Timo Kröger Nina Paaso Teollisuuden Voima Oy October 2006 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva. Kröger, T. & Paaso, N. 2006. Method development of gas analysis with Mass Spectrometer. Working Report 2006-41. Posiva Oy, Eurajoki. 94 p. ABSTRACT Dissolved gas content in deep saline groundwater is an important factor, which has to be known and taken into account when planning the deep repository for the spent nuclear fuel. Posiva has investigated dissolved gases in deep groundwaters since the 1990's. In 2002 Posiva started a project that focused on developing the mass spectrometric method for measuring the dissolved gas content in deep saline groundwater. The main idea of the project was to analyse the dissolved gas content of both the gas phase and the water phase by a mass spectrometer. The development of the method started in 2003 (in the autumn). One of the aims was to create a parallel method for gas analysis with the gas chromatographic method. The starting point of this project was to test if gases could be analysed directly from water using a membrane inlet in the mass spectrometer. The main objective was to develop mass spectrometric methods for gas analysis with direct and membrane inlets. An analysis method for dissolved gases was developed for direct gas inlet mass spectrometry. The accuracy of the analysis method is tested with parallel real PAVE samples analysed in the laboratory of Insinööritoimisto Paavo Ristola Oy. The results were good. The development of the membrane inlet mass spectrometric method still continues. Two different membrane materials (silicone and teflon) were tested. Some basic tests (linearity, repeatability and detection limits for different gases) will be done by this method. Keywords: Dissolved gases, groundwater sampling, MS, PAVE Kröger, T. & Paaso, N. 2006. Liuenneiden kaasujen massaspektrometrisen määritysmene- telmän kehitystyö. Työraportti 2006-41. Posiva Oy, Eurajoki. 94 s. TIIVISTELMÄ Pohjavesiin liuenneiden kaasujen koostumus tulee tietää ja ottaa huomioon, kun suunnitel- laan käytetyn polttoaineen loppusijoitustilaa. Posiva on tutkinut pohjavesiin liuenneiden kaasujen koostumusta jo vuodesta 1990 lähtien. Vuonna 2002 Posiva käynnisti kehitystyön, jonka päätarkoituksena on kehittää veteen liuenneiden kaasujen massaspektrometrinen määritysmenetelmä. Tavoitteena on analysoida veteen liuenneiden kaasujen koostumus sekä vesi- että kaasufaasista massaspektrometrillä. Tarkoituksena oli kehittää rinnakkainen analysointimenetelmä kaasujen kaasukromatografiselle analyysimenetelmälle. Yhtenä ta- voitteena oli testata voidaanko liuenneet kaasut analysoida suoraan membraani massaspekt- rometrillä. Työn tavoitteena oli kehittää kaasujen massaspektrometrinen analyysimenetelmä suo- rasyöttö- ja membraanitekniikoilla. Liuenneiden kaasujen analysointimenetelmä suorasyöt- tötekniikalla on kehitetty. Tämä kaasumaisten näytteiden analyysimenetelmä on testattu ja todettu luotettavaksi rinnakkaisnäytteillä. Rinnakkaisnäytteet analysoitiin Insinööritoimisto Paavo Ristola Oy:ssä. Nämä tulokset olivat hyviä. Vesinäytteiden menetelmäkehitystyö membraanisisäänviennillä jatkuu edelleen. Kaksi membraania (silikoni ja teflon) on tes- tattu. Membraanisisäänvientimenetelmän toteamisrajat, lineaarisuus ja toistettavuus tullaan testaamaan. Avainsanat: Liuenneet kaasut, pohjavesinäytteenotto, MS, PAVE 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ 1 BACKGROUND AND OBJECTIVES OF WORK.........................................5 2 INTRODUCTION TO MASS SPECTROMETRY.........................................7 2.1 Basic terminology.................................................................................7 2.2 Mass spectrometer...............................................................................8 2.3 Electron impact ionization (EI) .............................................................9 2.4 Quadrupole mass filter .......................................................................12 2.5 Detection of small ion currents...........................................................13 2.6 Vacuum.................................................................................................. .........................................................................................................14 2.7 Background gas .................................................................................14 3 MEMBRANE INLET MASS SPECTROMETRY (MIMS)............................17 3.1 General concepts...............................................................................17 3.2 Membranes ........................................................................................18 3.3 Membrane inlet design.......................................................................19 4 THE SAMPLER AND THE OPERATIONAL PRINCIPLE..........................21 5 SAMPLING................................................................................................23 5.1 The sampling procedure ....................................................................23 5.2 Evolution of the sampler.....................................................................24 6 MS-INSTRUMENT TESTING AND METHOD DEVELOPMENT...............25 6.1 Gas components................................................................................25 6.2 Instrument parameters.......................................................................26 6.3 Calibration constants used in gas analyses .......................................27 7 DIRECT GAS INLET TESTS.....................................................................29 7.1 Effects of sample pressure.................................................................29 7.2 Detection limits...................................................................................29 7.3 Effects of mass spectrometric pressure .............................................30 7.4 Effect of sample humidity ...................................................................32 7.5 Determination of calibration constants ...............................................33 7.6 Repeatability of gas analysis..............................................................34 7.7 Linearity of the signals .......................................................................35 8 DIRECT GAS ANALYSIS RESULTS OF GROUNDWATER SAMPLES...41 8.1 Sample OL-KR22/390-392 m.............................................................41 8.2 Sample OL-KR2/876-1050 m.............................................................41 8.3 Sample OL-KR6/422-425 m...............................................................44 8.4 Sample OL-KR6/135-137 m...............................................................46 8.5 Sample OL-KR6/125-130 m...............................................................47 2 8.6 Sample OL-KR6/98-100 m.................................................................48 8.7 Summary of PAVE sample analyses..................................................49 9 MEMBRANE INLET TESTS......................................................................51 9.1 Measurement parameters in membrane measurements....................51 9.2 Effect of temperature on the properties of a silicone membrane........52 9.3 Linearity of signals measured with membrane inlet and gas samples53 9.4 Gas components analysed directly from water with a membrane inlet ................................................................................................ 56 9.4.1 Calibration constants with a silicon membrane ........................... 56 9.4.2 Production of water samples with a known gas composition ...... 59 9.4.3 Linearity of signal intensities versus gas concentrations analysed directly from water....................................................................... 60 9.4.4 Repeatability of membrane measurements ................................ 68 10 SUMMARY................................................................................................71 10.1 The advantages and weaknesses of direct gas inlet mass spectrometry ....................................................................................71 10.2 Advantages and weaknesses of membrane inlet mass spectrometry72 10.3 Comparison of membrane and direct gas inlet methods....................73 REFERENCES.................................................................................................75 APPENDICES ..................................................................................................77 3 Used symbols and abbreviations CI = Chemical Ionization EI = Electron Impact Ionization FI= Field Ionization MCD = Multiple Concentration detection, same as MID with concentration calculation MID= Multiple Ion Detection. Measures only intensity of selected peaks (mass or m/z ratios) MIMS = Membrane Inlet Mass Spectrometry MS= Mass Spectrometry SIM = Selected Ion-Monitoring (mass or m/z ratios) mbar = Unit of pressure A = Unit of current, Ampere RSD = Relative Standard Deviation (standard deviation / average) IPROY= Insinööritoimisto Paavo Ristola Oy 4 5 1 BACKGROUND AND OBJECTIVES OF WORK Dissolved gas content in deep