The off-line and on-line analysis of liquid process streams by mass spectrometry

• Main Author: Dunn, Warwick Brian
• Other Authors: Green, John ; Townshend, Alan
• Published: University of Hull 1996
• Subjects: 660; Chemical engineering
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361495

The work presented in this thesis describes the development and validation in the laboratory of four techniques employed for the off-line and on-line analysis of liquid chemical process streams by mass spectrometry, without previous chromatographic separation of sample components. The four techniques were total vaporisation analysis, headspace analysis, membrane introduction mass spectrometry and atmospheric pressure ionisation-mass spectrometry. The technique of total vaporisation analysis completely vaporises liquid samples in a gas chromatograph heated injection inlet and analyses the vapour created with a mass spectrometer. Headspace analysis and membrane introduction mass spectrometry provide partial and selective transfer of compounds from the liquid sample phase to the gas phase and the subsequent analysis of the gas phase with a mass spectrometer. Headspace analysis has no third phase separating the liquid and gas phases whereas membrane introduction mass spectrometry places a membrane between the two phases. All three techniques were validated using an electron-impact quadrupole mass spectrometer and two model streams; acetone (analyte) in water and methyl iodide (analyte) in acetic acid. As an alternative strategy atmospheric pressure ionisation-mass spectrometers ionise samples in ion sources operating at atmospheric pressure. The techniques of electrospray ionisation and atmospheric pressure chemical ionisation were investigated for the analysis of formic, acetic and propionic acids present in water and other carboxylic acids. The techniques of total vaporisation analysis, headspace analysis and membrane introduction mass spectrometry provided low p.g m1' or g 11 limits of detection for acetone and methyl iodide with relative standard deviation values for replicate analyses of 100 pg ml' standards of less than 10 % in most cases. Off-line and on-line total vaporisation analysis and off-line headspace analysis provided accurate determination of acetone in similar process samples, whereas the matrix affected the accuracy of the determination when the techniques of on-line headspace analysis and membrane introduction mass spectrometry were employed. Electrospray ionisation could also detect formic, acetic and propionic acids in aqueous or carboxylic acid matrices at concentrations of and possibly less than 100 tg nil1 . Atmospheric pressure chemical ionisation could only detect carboxylic acids present in aqueous matrices at concentrations of 100 tg ml' or greater.