= m
= eV
= Hz


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UV Light
Beer's Law
Diode Array
Deuterium Discharge Lamp
Low Pressure Zinc Discharge Lamp
High Pressure Mercury Discharge Lamp
Low Pressure Cadmium Lamp
Tungsten Halogen Lamp
Lens and Window Material in Spectrometers
Fluorescence Reagents
Diffraction Grating
Fourier Transform IR Spectrometer
Halide Disks
Mull Samples
Film Samples for IR Spectroscopy
Light Pipes
Attenuated Total Reflectance Spectroscopy
Multiple Internal Reflectance
External Reflectance
Specular Reflectance
Diffuse Reflectance
Photoacoustic Spectroscopy
Beam Splitter
Raman Scattering
Rayleigh Scattering
Raman Spectroscopy
Atomic Spectroscopy
Atomic Emission Spectroscopy
Atomic Absorption Spectroscopy
The Inductively Coupled Plasma Torch
The Helium Plasma Torch
Emission Spectrometer
Atomic Absorption Spectrometry
Flame Atomic Absorption Spectrometer
Flame AA
Hollow Cathode Lamp
Electrothermal Atomization
Graphite Furnace
L’vov Platform
Electron Paramagnetic Resonance
Zeeman Effect
Continuous Wave
Electron Paramagnetic Resonance
Pulsed EPR
Electron Spin Echo
Multple Resonance Spectroscopy
Magnetic Resonance Spectroscopy
Nucleus Spin Decoupling in NMR
Superconducting Magnets
NMR Microcells
Electron Impact Ionisation
Chemical Ionization
Inductively Coupled Plasma Ionization
Secondary Ion Mass Spectrometry
Fast Atom Bombardment
Plasma Desorption Mass Spectrometry
Laser Desorption Mass Spectrometry
Matrix Assisted Desorption mass Spectrometry
Field Desorption Ionization
Thermospray Ionization
Electrospray Ionization
Atmospheric Pressure Ionization
Particle Beam Interface
Permeable Membrane Interface
Sector Mass Spectrometer
Quadrupole Mass Spectrometer
Ion Trap Mass Spectrometer
Time of Flight Mass Spectrometer
Optical RotationCircular Dichroism
Circularly Polarized Light
Verdet Constant
Faraday Effect

Permeable Membrane Interface

The membrane interface is only suitable for relatively volatile materials. However, as some environmental samples are contained in aqueous matrixes (e.g. the aromatic hydrocarbons in water, or certain pesticides in soil extracts etc.) the present stage of the interface development will be briefly considered for possible future use for sample solution ionization sources. One of the reports on the design and use of membrane inlet systems was that of Maden and Hayward, [43], who investigated a wide range of different materials for permeability and selectivity. The materials examined were silicone , two types of latex, polyethylene , polyurethane (polyether), polyurethane (polyester), a copolymer of acrylonitrile and butadiene and polyvinyl chloride. The design of the interface in which they tested the membranes is shown in figure 66. The membrane was positioned between two stainless steel blocks, and the entire interface was heated by a four-element heater.

The temperature controlled by means of a platinum resistance thermometer. The heaters were carefully located to ensure that the whole block was kept at an even temperature. The sample column eluent or flow injection sample, entered by a narrow channel 0.01 in. diameter, and then passed over the membrane and out through a larger channel, 0.02 in. diameter. The larger exit conduit helped reduce the pressure on the membrane, and prevented mechanical breakdown. The solutes diffused through the membrane under a concentration gradient that was naturally set up. On the other side of the membrane, the solute evaporated into the high vacuum of the mass spectrometer. The vapor then passed down a heated tube into the ion source.

Figure 66. The Membrane Interface for the Mass Spectrometer

The results indicated that as one might expect, some membranes were more efficient in the transfer of certain types of materials that others. If the membrane was made of a polymer that was naturally dispersive in nature (e.g. silicone membranes) then it would transfer dispersive type compounds such as hydrocarbons efficiently. In contrast, the silicone membrane would probably not be so effective for polar compounds such as methanol . Polar membranes such as the polyurethane or polyester would be likely transport polar materials such as alcohols more efficiently than hydrocarbons. It would appear that the membrane interface needs some more development work to be carried out before it might be considered as a competitor for the electrospray or API sampling systems. Nevertheless, it is an alternative approach, and one, which deserves further consideration.



About the Author
RAYMOND PETER WILLIAM SCOTT was born on June 20 1924 in Erith, Kent, UK. He studied at the University of London, obtaining his B.Sc. degree in 1946 and his D.Sc. degree in 1960. After spending more than a decade at Benzole Producers, Ltd. Where he became head of the Physical Chemistry Laboratory, he moved to Unilever Research Laboratories as Manager of their Physical Chemistry department. In 1969 he became Director of Physical Chemistry at Hoffmann-La Roche, Nutley, NJ, U.S.A. and subsequently accepted the position of Director of the Applied Research Department at the Perkin-Elmer Corporation, Norwalk, CT, U.S.A.
In 1986 he became an independent consultant and was appointed Visiting Professor at Georgetown
University, Washington, DC, U.S.A. and at Berkbeck College of the University of London; in 1986 he retired but continues to write technical books dealing with various aspects of physical chemistry and physical chemical techniques. Dr. Scott has authored or co-authored over 200 peer reviewed scientific papers and authored, co-authored or edited over thirty books on various aspects of physical and analytical chemistry. Dr. Scott was a founding member of the British chromatography Society and received the American Chemical society Award in chromatography (1977), the M. S. Tswett chromatography Medal (1978), the Tswett chromatography Medal U.S.S.R., (1979), the A. J. P. Martin chromatography Award (1982) and the Royal Society of Chemistry Award in Analysis and Instrumentation (1988).
Dr. Scott’s activities in gas chromatography started at the inception of the technique, inventing the Heat of Combustion Detector (the precursor of the Flame Ionization Detector), pioneered work on high sensitivity detectors, high efficiency columns and presented fundamental treatments of the relationship between the theory and practice of the technique. He established the viability of the moving bed continuous preparative gas chromatography, examined both theoretically and experimentally those factors that controlled dispersion in packed beds and helped establish the gas chromatograph as a process monitoring instrument. Dr. Scott took and active part in the renaissance of liquid chromatography, was involved in the development of high performance liquid chromatography and invented the wire transport detector. He invented the liquid chromatography mass spectrometry transport interface, introduced micro-bore liquid chromatography columns and used them to provide columns of 750,000 theoretical plates and liquid chromatography separations in less than a second. Dr. Scott has always been a “hands-on” scientist with a remarkable record of accomplishments in chromatography ranging from hardware design to the development of fundamental theory. He has never shied away from questioning “conventional wisdom” and his original approach to problems has often produced significant breakthroughs.

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