Tal Alon

Fast mass programming controller for a supersonic gas chromatography mass spectrometer

In a gas chromatograph mass spectrometer employing a quadrupole mass filter, molecules are ionized and transferred to a mass analyzer, where their mass to charge ratios (m/z) are measured. After the ionization step, the ions pass through a series of ion lenses that focus and guide them into the mass analyzer. The voltages on these lenses can be optimized for each specific m/z value (as the rest of the system is also optimized) to increase the number of ions reaching the mass analyzer. In certain cases, this dynamic mass-dependent optimization of the lenses can increase the signal by a factor of 2 or more. To implement this dynamic optimization, a digital circuit was developed, based on a digital signal controller and high-voltage (HV) amplifiers, that is able to optimize eight independent HV channels ranging between ±150 V at a rate of 100 µs.

Isotope abundance analysis for improved sample identification with tandem mass spectrometry

Tandem mass spectrometry (MS/MS) is widely used for trace level sample analysis in complex mixtures. However, sample identification in MS/MS is challenging and not as trustworthy as with electron ionization (EI) mass spectral libraries. This paper presents a novel method for the combination of isotope abundance analysis (IAA) and EI-MS/MS for improved sample identification even at trace level in complex matrices. Accordingly, the first quadrupole is scanned in a narrow range around the molecular ion group of isotopomers such as M+, [M+1]+ and [M+2]+, Q2 serves for collision-induced dissociation to produce product ions while Q3 transfers the major sample product ions with low resolution, thus encompassing and uniformly transmitting all the product ion isotopomers. IAA can then be used to derive elemental formula information from the cleansed experimental data. IAA-MS/MS was experimentally tested with perfluorotributylamine and a very good matching factor of 995 (out of 1000) was obtained for IAA on m/z 502, 503 and 504 (fragment ion isotopomers) while Q3 transmitted the m/z 264 product ion with a mass window of 6 m/z units. The IAA-MS/MS method was further tested with the pesticide diazinon on its molecular ions m/z 304, 305 and 306 while Q3 was locked on its m/z 179 product ion with a mass window of 6 m/z units. Again, very good matching factors were obtained, even for 40 pg diazinon on-column during its GC/MS analysis (match = 981). IAA-MS/MS combines the traditional benefits of MS/MS in the removal of matrix interferences with the IAA power of elemental analysis.

Comprehensive controller for super sonic molecular beam GC-MS

This paper presents a new, comprehensive digital circuit used for the control of a novel Gas Chromatograph Mass Spectrometer (GC-MS) interface that is based on Supersonic Molecular Beam (SMB). The circuit includes a Texas Instruments 150MHz digital signal controller (DSC), high voltage amplifiers for 8 independent channels and 4 independent channels of high resolution PWM. The circuit, along with a sophisticated embedded program and a custom made PC application, control all aspects of the interface: smart filament emission-current stabilization, static and scanning mass-dependent ion-source voltages, transfer-line heater PID controls with thermocouple feedbacks, on/off valves, relays and several peripheral device controls that enable the full operation of a turbo-molecular vacuum pump, and of gas flow and pressure controllers. All aspects of this comprehensive controller were successfully tested and it is already being used by several analytical chemists around the world for the control of the Aviv Analytical 5975-SMB GC-MS with Cold-EI.

Fast mass programming and PWM controllers for super sonic GC-MS using DSP

In a Gas Chromatograph Mass Spectrometer (GC-MS) employing a quadrupole mass filter, molecules are ionized and transferred to a mass analyzer, where their mass to charge ratios (m/z) are measured. After the ionization step, the ions pass through a series of ion-lenses that focus and guide them into the mass analyzer. The voltages on these lenses can be optimized for each specific m/z value (as the rest of the system is also optimized) to increase the amount of ions reaching the mass analyzer. In certain cases this dynamic mass-dependent optimization of the lenses can increase the signal by a factor of 2 or more. In addition, any GC-MS interface requires that the molecules vaporized and separated by the Gas Chromatograph (GC) will be transferred into the Mass Spectrometer (MS) at high temperature in order to avoid condensation. Any GC-MS and especially those with a supersonic molecular beams interface can benefit from the ability to change the temperature of this transfer-line between the GC and MS. To implement this dynamic optimization a digital circuit was developed, based on a digital signal controller and high voltage amplifiers that is able to optimize 8 independent high voltage channels ranging between ±150 V at a rate of 100 μs. In addition, 4 independent channels of high resolution PWM unit within the above mentioned controller was utilized in order to control the temperature.