Atoms of different elements have different masses in amu or Daltons, such as H=1, C=12, and O=16. If we measure the mass of individual atoms and molecules within a gas mixture like lab air or an atmosphere, we can identify the chemical compounds it contains.
A mass spectrometer gives us a spectrum with peaks, as seen below.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Time-of-flight mass spectrometry (TOF-MS) determines molecular mass by measuring how long ions take to travel a certain distance. Other mass analysis options are available, such as magnetic sector, quadrupole, or ion trap, but at Kore we focus exclusively on TOF. This is because of its unlimited mass range, excellent mass resolution and sensitivity, and, most importantly, its high speed – making it the perfect technique for real-time analytical paradigms.
First, a neutral molecule is charged using an ion source, allowing it to be manipulated by electric fields. The flight chamber is evacuated to ultra-high vacuum so that ions can travel without collisions, operating in a molecular flow regime. Ions are then extracted by electrostatic fields into a flight tube held at a high-voltage potential E, and this extraction pulse defines the start time, T=0s.
Once inside the field-free region of the flight tube, each ion carries approximately E kinetic energy. From the conservation of energy (E=1/2 mv2), it follows that heavier ions travel more slowly through the tube. The instrument times each ion’s journey from the extraction region at T=0 until it strikes the detector, with lighter ions arriving before heavier ones. This produces a spectrum.
Finally, by analysing these flight properties, the system uses fundamental physical relationships to accurately deduce the mass of each ion.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
In real systems, extracted ions exhibit a Gaussian spread of initial kinetic energies rather than a single, uniform value. Consequently, the signal at the detector is not an infinitely narrow point but a broadened peak. In the drift space, higher-energy ions travel faster and arrive sooner, meaning flight time decreases as energy increases (a negative relationship, or dt/dE < 0).
To decouple flight time from initial energy variation, TOF-MS typically incorporates a reflectron: an electrostatic mirror. In the reflectron, more energetic ions penetrate more deeply before being reflected, extending their total flight time and giving the opposite effect (a positive relationship, or dt/dE > 0).
Software control of the deceleration and reflectron voltages precisely adjusts the time ions spend within the mirror. This tuning provides the primary control for minimising mass-peak width and optimising mass resolution.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
The TOF-MS source region is where ions are extracted into the flight tube. Within this region, ions begin with varying initial positions and velocities.
When a high-voltage pulse is applied to the extraction electrode, T = 0 is defined, and a wedge of ions is extracted toward the final high-voltage electrode at the entrance to the field-free region. This wedge of ions is shaped by crossed-beam geometry. Because ions start from different positions in the source, they acquire different kinetic energies during extraction.
For the extraction pulse itself, only the amplitude and the leading edge matter. The pulse width is not important, since ions that enter the extraction field after the leading edge or between extraction pulses do not follow the ideal trajectory and hit the chamber walls.
The reflectron can compensate for either spatial spread (different start positions) or velocity spread (different initial velocities), but it cannot fully correct for both simultaneously. To minimise the velocity component along the TOF-MS flight axis, the beam is therefore best injected orthogonally (at 90°) and as parallel as possible. The quality of this incoming beam directly limits the best achievable mass resolution.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
The extract pulse is synchronised to the 4 GHz Kore time-to-digital converter (TDC). When the pulse is applied to the extraction electrode, ions begin their flight and the Kore TDC simultaneously registers T=0s.
Flight time is measured from the leading edge of the extraction pulse to the ion’s arrival at the detector. Most molecules arrive within a window of 4 to 50µs, with a time resolution better than 1ns.
The TDC can either be set to an internal or external trigger mode:
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
In analogue mode, the system measures similar to a fast digital oscilloscope with averaging capability. This allows Kore to generate an easily measurable electronic pulse from even a single ion arrival, while still retaining the full peak shape information.
In digital mode, the system counts single ions, recording the time of each pulse. A key limitation is that if two or more ions arrive simultaneously, only one event is registered. Kore deals with any oversaturated signal by performing a saturation correction. Typically, 10 to 50 ions reach the detector per extraction pulse. In digital mode, these events are amplified and digitised to build statistically meaningful data. Then, the Kore software sums the information across many extraction pulses at a repetition rate of up to 50 kHz.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
The raw data stream from the TDC is a simple sequence of numbers collected over many TOF extraction cycles. Each entry corresponds either to a cycle-start marker or to an individual ion arrival time.
To construct a spectrum, the ion arrival times are binned into a time-histogram, where each bin records the number of ions arriving within that specific time interval. This time-histogram is saved as the raw data file.
To view, we normally convert time to mass, creating a mass histogram using Equation 1, where t0 and Cb are determined during a mass calibration.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
Caption in here lorem ipsum dolor sit amet, consectetur adipiscing elit.
To discuss any requirements, please get in touch with our friendly team.
Dae parum ullendamet pera ipieturit esectis necae eum.
Dae parum ullendamet pera ipieturit esectis necae eum.