LTQ-FT-ICR (Thermo)

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Domain of applications

Identification of proteins in simple mixtures (direct injection), on in complex mixtures following a 1D or 2D LC separation.

Determining exact masses of modifications

Peptide quantification following an ITRAC or SILAC labeling

Measurement principle

Peptides obtained by protein hydrolysis are separated by 1D or 2D chromatography.
At atmospheric pressure, droplets are formed at the end of a fine capillary held at a high potential. The intense electric field provides these droplets with an important charge density. Under the effect of this electric field, the liquid is transformed into a cloud of fine charged droplets (spray) that evaporate progressively. Their charge density being too high at this points, the droplets explode thus liberating micro-droplets containing protonated and deprotonated analyte molecules, bearing a variable number of charges.

The ions thus created are then guided by successive electric potentials applied to the sampling cones and acting as a barrier with the following sections that are maintained under high vacuum (<10-5 Torr). During this travel at high pressure, ions undergo multiple collisions with gas and solvent molecules which helps complete the desolvation process. By varying the electric potentials in the source it is possible fragmentation phenomenons that are more or less important.
This method thus produces multiply charged ions.

These ions enter the ICR analyzer to be separated according to the mass/charge ratio. The ion cyclotron resonance analyzer is constituted of an ICR cell that usually contains six isolated plates with an applied voltage. Ion acquire their movement in the (xy) "cyclotronic" plane, ie circular and uniform with a frequency f= eB/(2π.m/z). Once trapped in the cell, the ions follow the same trajectory but not the same position at a given moment. The ions are accelerated, put in phase and the radii of the their orbits increase. The current that is induced by the coherent movement of ions having the same m/z is measured by the detection plates: a damped sine wave with a cyclotronic frequency. The total induced current is the sum of all the damped sine waves of the cyclotronic frequencies corresponding to the ions excited by resonance. Since the cyclotron frequency is proportional to 1(m/z), the inverse of the current’s Fourier transform gives access to the m/z pass spectrum.

Technical characteristics

Instrument : LTQ FT-ICR Thermo Electron
Ionisation source : ESI
Analyzer : LTQ-FT-ICR
Sensibility :
Precision : 5-10 ppm
Resolution : 100 000
Mass range : up to 27000 Da
Monitoring and data processing : PC (windows), Mascot

Installation date:


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