An Approach to the Design of Mass-correlated Delayed Extraction in a Linear Time-of-flight Mass Spectrometer

Abstract

An algorithm is suggested that allows the implementation of first order velocity (energy) focusing in a linear, single field, time-of-flight mass spectrometer (TOF/MS) over a broad mass range using a time-dependent mass-corrected extraction field. The interpolation formula for extraction field dependence on time for a particular geometry of TOF/MS is presented. There are two values that determine the expression for temporal dependence of the extraction field: the geometry scale parameter (the ratio of the ion source and field-free drift tube lengths) and the initial point (low-mass limit) of scanning in the mass spectrum. © 1997 by John Wiley & Sons, Ltd. Received 17 January 1997; Accepted 27 January 1997 Rapid Commun. Mass Spectrom. 11, 433-436 (1997 Here, DE provides reduced energy losses during the initial stage of ion drift through desorbed gaseous matrix substance in the extraction field.The main problem of the velocity focusing using DE is the narrow mass range in focus because the optimum time delay, T, is a mass-dependent parameter. In the single-field linear TOF mass-spectrometer: . The quality of the mass spectra is gradually degraded on moving away, to both sides, from the optimum value of m 0 . The need to obtain a broad, high quality mass spectrum, especially for fragmentation studies of large nucleotides and proteins has, stimulated the search for ways to overcome the limitations inherent in the conventional DE method. THEORYLet us consider the standard, linear, single-field TOF mass spectrometer. Also consider a model, broadrange, mass spectrum ranging from the low-mass limit, m 0 , to the high-mass limit M 0 .First, the time delay, T, is chosen to provide optimum energy focusing conditions only for the low-mass limit (m 0 ) ion. At the moment that the ion of mass m 0 reaches the exit grid of the ion source (the plane x = d), the extraction field is slightly adjusted to improve focusing conditions for the subsequent ion of mass m = m 0 + δm.The strategy is formulated as follows. It is necessary to restore a time dependence of the extraction-field function U(t) that enables first order energy focusing for every successive ion of mass m > m 0 . One can define a reduced voltage function u(t) = U(t)/U 0 , for which t ≥ T, (U(t = T) = U 0 ). Then, for an ion of mass m, the equation of motion in the ion source is:Upon integration of (2) this gives:

Mass correlated acceleration in a reflectron MALDI TOF mass spectrometer: an approach for enhanced resolution over a broad mass range

“…The theory of MCA has been explained previously [15][16][17]. The concept of the method was described by Kovtoun employing both single-stage [15] and dual-…”

<title>Formation of subfemtosecond photoelectron bunches in time-dependent electric fields</title>

“…Suggested is an analytic model of the first-order temporal focusing in the time-dependent field representing a quadratic potential well Iraveling with a constant speed along the direction ofthe bunch propagation. 3 . A system of two linear differential equations describing evolution of the first-order temporal aberration and the first variation of the particle' full energy along the principle trajectory is derived.…”

“…Hereafter the dot denotes differentiation with respect to time, while the stroke denotes differentiation with respect to z-coordrnate. The initial conditions at the photocathode take the form z(r;r,,)=0, (3) Any particle trajectory can be expanded into a power series with respect to the small parameters r, , With regard to axial symmetry of the system, such an expansion will contain only the integer powers of the radial energy component 8r Withifl the first-order approximation with respect to r, , we obtain z(t ; = zo(t)+zr(t) r+z(t)j+... (4) The differential equations for the variations z and z in (4) as well as the initial conditions for those equations can be easily derived from (2) and (3) by varying with respect to the parameters and on the principal trajectory:…”

A miniaturized matrix‐assisted laser desorption/ionization time of flight mass spectrometer with mass‐correlated acceleration focusing

“…The theory of MCA has been described previously 25, 26. The technique has been put to practice in both linear27 and reflectron28 MALDI‐TOF mass spectrometers.…”