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Instrument Database:
comstock Incorporated - mini Tof II
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| Year of introduction |
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| Status |
available |
| Company |
comstock Incorporated
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| Categories |
Mass spectrometer: General
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The miniTOF® II mass spectrometer system provides fast answers to mass analysis questions at low cost. Complete with TOF, heated ion source, vacuum chamber and pumps, all necessary detection and control electronics, Windows-based software and power supplies for analysis of positive ion spectra, the miniTOF® II system is suitable for both laboratory and for OEM uses. NIST library search capability is available. Applications include fast GC-MS with storage of up to 100 averaged spectra per second, gas and headspace monitoring and analysis. Specifications include mass resolution of better than 1 Da for the mass range from 0 to over 600 Da, cycles rates to 20 kHz, and ppm level sensitivity. System dimensions are approximately 21”(D) x 13”(W) x 22” (H), excluding PC, CRT and rotary vane pump.
MECHANICAL
Comstock miniTOF® II is comprised of a vacuum vessel with a linear TOF spectrometer inside, a PC system meeting today’s standards, an external power supply box, and vacuum pumps. Vacuum seals are Viton O-rings. (Seals of other materials may be used. Contact factory.)
Location of Major Components The spectrometer itself is attached to the inside of the front panel of the vacuum vessel, and a small satellite power supply is on the other (air) side past electrical feedthroughs. The main power supply is in a metal box, often placed underneath the vacuum vessel. The Time-to-Digital Converter, control firmware, and digital as well as analog interfaces are on a single specially designed PC card and housed in the PC tower. A turbomolecular vacuum pump(70 l/s) is also attached to the vacuum vessel. A foreline pump (0.95 cubic meters/hour) is normally placed on the floor. A port on the vessel for a vacuum gauge is optional.
ELECTRONICS
Power Supplies
Generates all the voltages and currents necessary to operate the spectrometer. A number of these voltages are singly or doubly regulated for the precision operation of the system.
Time-to-Digital Converter
Resides on a PCI card housed in the PC. It converts the time elapsed between repeller time and detection at the end of the flight into a digital form, when the information is transferred from the clock to a FIFO memory. Multiple stops are allowed to each start. One count is recognized for each of the stops regardless of the amplitude of the signal from the detector so long as it exceeds the discriminator level. The time data stored in the FIFO memory is transferred to the PC memory on firmware command. The time resolution of the clock (bin width) is 10 nanosecond. Time count is 32 bit long. The event count capacity used in the PC is 64 bits.
PC Interface/Controls
Digital and analog I/O interface ports are available on the PC card, most of which are used for the systems purposes. The use of extra ports for additional functions are possible but requires special engineering and programming. Contact factory.
Safety Interlocks
In order to safeguard the spectrometer components inside the vacuum vessel, a special sensor in the turbomolecular pump signals the pressure inside the vessel. Voltages are disabled until a proper vacuum is reached.
SPECTROMETER
General
The spectrometer is a linear, orthogonal injection, electron impact ionization Time-of-Flight spectrometer. The entire instrument, from sample intake to ion detector and gas exhaust is carefully designed and carefully machined for optimum space and time focusing. Standard sample inlet is a non-fractionating capillary on Cajun connector mounted on the front panel of the vacuum vessel. (Other sample inlet arrangement is possible. Contact factory.) The flight path is about 40 cm from repeller to detector. The detector is a discreet dynode type for sensitivity and ruggedness.
Operation
Operating parameters are set on the PC screen and communicated to the power supplies via the interface board. Filament current and detector bias are monitored back on the PC screen so that the operator can be assured that there is no significant deviations. A device in the vacuum pump detects a low vacuum. System uses the signal to disable voltages.
Upkeep
The entire spectrometer is mounted on the vacuum side of the front panel to ensure easy access. Electron emitting filament is positioned by two screws that are easily accessible. It takes less than 30 minutes from the time the vacuum pumps are turned off until they are turned back on with a new filament inside.
PERFORMANCE*
Mass Resolution M/dM resolution of 600 is guaranteed. Typical resolution as it is tested at the factory is about 1,000. It is possible to tune the resolution up higher.
Mass Range
1 ~ 600 nominal.
Stability Peak shift
< 0.02% over 24 hours. Peak broadening not observed over 24 hours.
Minimum Detection Limit
< 5 ppm without pre-concentration. The limit is a function of measurement time (= number of sweeps).
Dynamic Range
The dynamic range is a function of measurement time and discriminator setting, among other parameters. Due to the nature of TDC counting, the dynamic range, defined as the maximum count that can be stored in the system divided by the least significant count, can be an extremely large number. The maximum event counts (the vertical scale on the spectrum display) is 2^64. One needs to estimate the number of counts in background noise accumulated during the time. The noise count is directly influenced by the discriminator setting.
Mass Calibration
Carried out on quadratic model based on three or more data points. Single set of coefficients over the mass range. Calibration coefficients could change significantly when detector voltage is changed. Operating software issues a warning in a pop up window when it sees an old mass calibration. Operator defines how old is old. When the software does not see calibration performed for that voltage, it refuses to convert the time scale (horizontal) to mass scale.
SOFTWARE
Labview® The programs provided with the system are written in LabView® language under Windows OS. They cover set up of operational parameters, data acquisition, data handling between TDC and PC and inside PC, display, and mass calibration. A hook to the search engine for NIST’s MS library as well as access to the library data itself are available. If an additional function is needed, contact factory.
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