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Characteristics of time-of-flight mass spectrometers
Abstracts The relative importance of ion source and quadrupolc filters in determining long term stability will be discussed. By comparing the long term stability of the normal mode of operation with the ac onI> mode of operation it can be shown that it is often the source which is the critical component. This work was supported by and carried out in co-operation with the UKAEA Laboratories Culham and the National Physical Laboratories at Teddington.
Referenctu:
1’7
polyatomic molecules. Indirect identification through the use ot known isotopic abundances. understanding of chemical structure and stability and ion source induced molecular fragmentation patterns is possible. however. Examples of indirect identification arc given. The quadrupole type analyser has supplanted nearly all other partial pressure analyscrs during the past IS yr, primarily due to its inherent high sensitivity and easily accomplished resolutionscnsitikity trade-off. Because of the case with which the ‘resolution’ cm be adjusted, instruments can be and often arc misadjusted. Through the USC of ‘standard’ fragmentation patterns and an appropriate calibrated leak it is possible to readily detect any misadjustmcnt of the quadrupole’s sensitivity or resolution. Examples of these techniques are given.
(IUXJJ. Vacuum measurement calibration system at PPPL*
Characteristics of time-of-flight
W R Blanchard and D Doersam, Plusmu
mass, spectrometers
Prirwton
The basic operating principles of typical time-of-flight mass spectrometers are outlined. Instruments of this type can be used as residual gas analysers over a wide range of pressures. Desirable features include the absence of magnetic fields. relatively simple construction, non-critical alignment, and a large ion current for a given background gas pressure. Other useful characteristics include: an inherently very rapid mass sweep rate (usually a feu tens of microseconds per mass spectrum) and a very wide mass range (usually extending to at least 500 amu). A number of specialized time-of-flight residual gas analysers are discussed. The smallest have ion flight paths of approximately 4 cm and can operate at pressures above IO-’ torr. Others have ion flight paths of up to 130 cm and can detect partial pressures well below lo- I2 torr. Factors affecting stability and mass discrimination are summarized.
Fragmentation and isotopic abundance as a means for identifying vacuum gaseous species and for monitoring partial pressure analyser operation 1. C Beavis, Photovoltaic Sundiu
Nutionai
87185.
L’SA
Concentrcctor
Luhoratories,
Research
Alhuyueryue,
New
PO Boz
PhJ,sic.s
451. Princeton.
NJ
Luhomtor,v. 08544.
USA
A vacuum measurement system has been fabricated for the calibration of residual gas analysers, ion gauges and capacitance manometers in use at the Princeton University Plasma Physics Laboratory (PPPL). The system is also used to check the stability of secondary (or transfer) vacuum measurement standards (I torr capacitance manometers) against our primary vacuum standard. a spinning rotor gauge. The calibration setup consists of a turbomolecular-pumped ultra-high vacuum system with the standard ion gauge. capacitance manometer, spinning rotor gauge and test gauge manifold located on separate isolation valves. Any one ofeight gases from ;I gas manifold can be introduced into the calibration system through a piezoelectrically-controlled leak valve. Quick changeovers from one gas to another are accomplished by the use of a separate pumpout system and vacuum regulators on the gas manifold. Both the calibration system and gas manifold are controlled and monitored with an IBM PC-based data acquisition system. Using this system calibrations of different ion gauges and capacitance manometers over the pressure range IO- ’ 10 ’ torr. have become routine and a data base is being acquired. In a recent calibration four ion gauge controllers were calibrated for three separate gases in less than 4 hr.
Dicision. Mrrko
The purpose of this presentation is to demonstrate that molecular fragment ions and isotopes are useful markers not only for identifying gaseous species in a vacuum system but also to assure that the partial pressure analyser is performing as expected. Partial pressure analysis is ordinarily performed with a mass analyser system which is attached directly and semi-permanently to the vacuum system to be measured. Such mass analysers are characteristically of higher sensitivity and lower resolution when compared to the traditional stand-alone mass spectrometer. Because of the relatively low resolution. typically I 2 amu ‘. it is impossible to directly and unequivocally identify most 630
C:nioersity.
Calibration of a gas-analytical R Dobrozemsky, 4-2444
Srihersdo~f,
MS by defined gas bursts
Ostrrrc,ic~l~isc~/Irs Forsc,hung\I~,/Itrnrtl
Srihcrsdo~~f.
.Austritr
The aim of our work is to calibrate a mtcroprocessor-controlled quadrupole. mainly used to determine small gas amounts (from TSD. outgassing, gas-content measurements of metal:. minerals. etc). The analysis should give: (I ) the absolute amount of gas
Referenctu:
1’7
polyatomic molecules. Indirect identification through the use ot known isotopic abundances. understanding of chemical structure and stability and ion source induced molecular fragmentation patterns is possible. however. Examples of indirect identification arc given. The quadrupole type analyser has supplanted nearly all other partial pressure analyscrs during the past IS yr, primarily due to its inherent high sensitivity and easily accomplished resolutionscnsitikity trade-off. Because of the case with which the ‘resolution’ cm be adjusted, instruments can be and often arc misadjusted. Through the USC of ‘standard’ fragmentation patterns and an appropriate calibrated leak it is possible to readily detect any misadjustmcnt of the quadrupole’s sensitivity or resolution. Examples of these techniques are given.
(IUXJJ. Vacuum measurement calibration system at PPPL*
Characteristics of time-of-flight
W R Blanchard and D Doersam, Plusmu
mass, spectrometers
Prirwton
The basic operating principles of typical time-of-flight mass spectrometers are outlined. Instruments of this type can be used as residual gas analysers over a wide range of pressures. Desirable features include the absence of magnetic fields. relatively simple construction, non-critical alignment, and a large ion current for a given background gas pressure. Other useful characteristics include: an inherently very rapid mass sweep rate (usually a feu tens of microseconds per mass spectrum) and a very wide mass range (usually extending to at least 500 amu). A number of specialized time-of-flight residual gas analysers are discussed. The smallest have ion flight paths of approximately 4 cm and can operate at pressures above IO-’ torr. Others have ion flight paths of up to 130 cm and can detect partial pressures well below lo- I2 torr. Factors affecting stability and mass discrimination are summarized.
Fragmentation and isotopic abundance as a means for identifying vacuum gaseous species and for monitoring partial pressure analyser operation 1. C Beavis, Photovoltaic Sundiu
Nutionai
87185.
L’SA
Concentrcctor
Luhoratories,
Research
Alhuyueryue,
New
PO Boz
PhJ,sic.s
451. Princeton.
NJ
Luhomtor,v. 08544.
USA
A vacuum measurement system has been fabricated for the calibration of residual gas analysers, ion gauges and capacitance manometers in use at the Princeton University Plasma Physics Laboratory (PPPL). The system is also used to check the stability of secondary (or transfer) vacuum measurement standards (I torr capacitance manometers) against our primary vacuum standard. a spinning rotor gauge. The calibration setup consists of a turbomolecular-pumped ultra-high vacuum system with the standard ion gauge. capacitance manometer, spinning rotor gauge and test gauge manifold located on separate isolation valves. Any one ofeight gases from ;I gas manifold can be introduced into the calibration system through a piezoelectrically-controlled leak valve. Quick changeovers from one gas to another are accomplished by the use of a separate pumpout system and vacuum regulators on the gas manifold. Both the calibration system and gas manifold are controlled and monitored with an IBM PC-based data acquisition system. Using this system calibrations of different ion gauges and capacitance manometers over the pressure range IO- ’ 10 ’ torr. have become routine and a data base is being acquired. In a recent calibration four ion gauge controllers were calibrated for three separate gases in less than 4 hr.
Dicision. Mrrko
The purpose of this presentation is to demonstrate that molecular fragment ions and isotopes are useful markers not only for identifying gaseous species in a vacuum system but also to assure that the partial pressure analyser is performing as expected. Partial pressure analysis is ordinarily performed with a mass analyser system which is attached directly and semi-permanently to the vacuum system to be measured. Such mass analysers are characteristically of higher sensitivity and lower resolution when compared to the traditional stand-alone mass spectrometer. Because of the relatively low resolution. typically I 2 amu ‘. it is impossible to directly and unequivocally identify most 630
C:nioersity.
Calibration of a gas-analytical R Dobrozemsky, 4-2444
Srihersdo~f,
MS by defined gas bursts
Ostrrrc,ic~l~isc~/Irs Forsc,hung\I~,/Itrnrtl
Srihcrsdo~~f.
.Austritr
The aim of our work is to calibrate a mtcroprocessor-controlled quadrupole. mainly used to determine small gas amounts (from TSD. outgassing, gas-content measurements of metal:. minerals. etc). The analysis should give: (I ) the absolute amount of gas