The analysis of organic and inorganic samples by fast flow glow discharge mass spectrometry

• Main Author: Newman, K.
• Published: Swansea University 2006
• Subjects: 543
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638317

This thesis reports the development and characterisation of the fast flow argon flow discharge source, coupled to quadrupole mass spectrometry, as a novel detector for gas chromatography. Also described are fundamental studies of the chemical and electrical properties of the flowing plasma, which further support the excited state model proposed in previous publications from this laboratory. The fast flow glow discharge source has been used for the GC-MS analysis of simple mixtures of halocarbons and organotin compounds. Detection limits in the low and sub-picogram range were obtained and the technique is shown to be a robust, simple and low cost alternative to existing plasma sources for elemental speciation. The voltage applied to the ion sampling cone has been used to easily control the degree of fragmentation of organic samples. When a small (< 10 V) <i>positive </i>bias was applied, molecular mass spectra were obtained with detection limits < 1 pg. When a <i>negative </i>bias was applied, the sample fragmented and dispersed the charge, which lowered the sensitivity. A progression to more fragmented ions was observed as the voltage was increased. This was similar to the type of information obtained from tandem mass spectrometry but only a single quadrupole was used in this work. The effect of the ion exit voltage on the organic ion intensities has been shown to be consistent with a secondary discharge of argon Rydberg (highly excited) states close to the sampling cone. When a negative bias is applied, the sample is fragmented in collisions with electrons accelerated in the field. When a positive bias is applied, positive ions are repelled but neutral molecular Rydberg species can pass through the exit aperture to the mass spectrometer, where they are then ionised. Therefore, the molecular mass spectra obtained may be considered as a form of Rydberg state mass spectrometry.