The Application Notebook
Resistive glass tubes and plates are designed to guide ions by generating a uniform electric field. PHOTONIS resistive glass products are composed of a proprietary lead silicate glass that has been specially processed to create a resistive layer at the surface. The resistivity can be varied over several orders of magnitude to suit the specific application.
Resistive glass is manufactured by using a hydrogen firing process to create an integral semi-conductive layer on the surface. This reduced lead silicate layer is typically several hundred angstroms thick. Resistive glass can be formed into plates, tubes, cylinders, sheets, washers, or other shapes. The products are resistant to scratches from light to moderate abrasions, and can easily be cleaned ultrasonically with water, acetone, methanol, or IPA without degrading the performance.
One application of resistive glass is capillary inlet tubes for atmospheric pressure ionization sources. Single capillary inlet tubes made from resistive glass significantly improve ion transfer efficiency when compared to conventional quartz inlet tubes. Voltage applied across nickel-chromium electrodes at each end of the inlet tube creates an electric field that preferentially attracts either positive or negative ions. Polarity switching can also be accomplished more quickly than with conventional inlet tubes.
The properties of resistive glass help prevent ions from colliding with the tube walls and with each other, reducing ion loss and resulting in a more efficient sample transfer by forcing more ions into the mass spectrometer.
PHOTONIS has also developed a multicapillary resistive glass inlet tube. A proprietary multibore extrusion process creates a circular array of six individual channels in the same footprint as a single capillary inlet tube (see Figure 1).
Figure 1: PHOTONIS’ multi-capillary resistive glass inlet tubes offer six individual channels in a standard footprint.
Multicapillary resistive glass inlet tubes provide increased sensitivity by further improving ion transmission when compared to single capillary inlet tubes.
Tubes made from resistive glass can also be used in other mass spectrometry applications, such as for drift tubes, collision cells, ion mirrors, voltage dividers, or reflectron lenses.
Another application of resistive glass is for use in ion mobility spectrometry drift tubes. Resistive glass drift tubes operate on the same principle as capillary inlet tubes, and demonstrate a similar improvement in ion transmission. The solid tube body also provides containment for counter-flow gas, eliminating the need for an additional enclosure.
An increase in ion transfer efficiency by a factor of 100 has been reported from using PHOTONIS single capillary inlet tubes.
An increase in ion transmission of up to 10 × using multicapillary tubes when compared to single capillary inlet tubes has been achieved by a leading mass spectrometer manufacturer, dramatically enhancing instrument sensitivity. Resistive glass multicapillary tubes therefore provide an increase in ion transfer efficiency of up to 1000 × when compared to conventional quartz tubes.
A demonstrated improvement in ion transmission is also realized with the use of single-piece construction resistive glass IMS drift tubes when compared to traditional multipiece lens and ring assemblies.
Resistive glass reflectron tubes provided equal or better performance in an orthogonal TOF system. This comparison showed superior resolution, indicating better energy focusing, while spectra between the two were nearly identical.
Overall, resistive glass tubes offer benefits to a variety of mass spectrometer applications, many of which can be realized by replacing an existing tube with one made from resistive glass.
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