THE NIBTRON ION SOURCE.
A major breakthrough in quadrupole mass spectrometry has been achieved by ASI with the introduction of the NIBTRON ion source. This Ion Source is available as an option, on the ASI quadrupole gas analysis systems and provides the following advantages and unique features:-
1) Elimination of 99.9% or more of the interfering background peaks.
2) Provides greatly improved accuracy and performance.
3) Allows much simpler, lower pumping speeds, and hence much lower cost vacuum systems.
4) Eliminates the need for bake-out ovens.
5) Allows much smaller gas samples to be measured.
6) Reduces memory effects from previous gas samples
7) Eliminates catalytic reactions from the hot filament being measured.
8) CO and CO2 from tungsten filament eliminated.
9) Sample gas measurement not affected by variations in pumping speed, or gas discrimination.
Portable Mass Spectrometer systems
Both the AX200 and AX600 mass spectrometers are small low power (16W/20W) mass spectrometers. When fitted with the NIBtron Ion Source they are ideal for portable battery powered gas analysis systems using small ion pumps. The gas load on the pump is 10 times lower than a conventional ion source to produce the same signal current. The sample gas can be can be further reduced because of the absence of background peaks. Therefore the total gas load on the pump can be reduced by a factor of 100 or more. This light gas load on Ion pumps greatly reduce problems of argon instability, the possibility of stalling the ion pump and reduces the power requirements of the pumping system.
CONVENTIONAL ION SOURCES. Ionise both the sample gas and the residual gases present in the vacuum system. These residual background peaks often make gas analysis very difficult. To reduce these background peaks to acceptable levels it is essential to frequently bake the vacuum system to high temperature. Even after bake out, residual peaks are still present, limiting the accuracy to which gas analysis can be achieved. These residual peaks will subsequently increase in amplitude when sample gas is introduced into the vacuum chamber due to desoption from the chamber walls, making it difficult to determine the percentage of sample peak that may be present in a changing background.
NIBTRON. The new NIBTRON quadrupole analyser has an extremely low sensitivity to residual gas ions, whilst at the same time has a high sensitivity to sample gas ions introduced via the inlet probe. This improvement in ionisation ratio is in excess of 2000, producing clean sample gas spectra even under poor vacuum/high background conditions.
This is illustrated below. The following two scans were made using a two small ASI RGA mass spectrometers. One fitted with a standard electron impact source and the second with a NIBTRON source. They were operated together on the same vacuum system under identical vacuum conditions and cover the mass range from approx. 32-50amu. The test were deliberately carried out on a oil contaminated vacuum chamber to produce a very high background of residual gases . The system pressure was at 3 x 10-6 mBar. A leak valve was then opened, admitting an air sample, increasing the pressure by 1 x 10-6mBar.
NOTE 1:- Because of its very low sensitivity to residual background gases, the NIBTRON is totally unsuitable for fitting to existing vacuum systems for Residual Gas Analysis Applications. It will only analyse gases introduced via the NIBTRON gas inlet probe.
NOTE 2:- The NIBTRON ION SOURCE is unique to Anglo Scientific Instruments and should not be confused with a technique used by other manufactures whereby a background spectra is sampled and stored. Gas is introduced and then the stored background is subtracted from the sample + background spectra. This technique has limited use because the background spectra is frequently changing with time and the introduction of the sample gas will cause further changes in the background gases due to adsorbtion and /or desorbtion of gases from the chamber walls caused by pressure changes within the vacuum chamber. Because the background is now different to the stored background The result can give rise to large errors particularly on smaller peaks. Some peaks may be present that do not exist and others that should be present are not shown. The result of some peaks indicate a negative result..
The NIBTRON ion source is a vastly superior technique completely free of these errors