Improved calibration of time-of-flight mass spectra by simplex optimization of electrostatic ion calculations.

A novel time-of-flight mass calibration method has been developed. In contrast to conventional methods, where the relationship between ion flight time and mass is an arbitrary polynomial equation, this method is based on the physics of ion motion. Parameters needed to describe the physics are numerically optimized using a simplex algorithm. Once these parameters are established, unknown masses can be determined from their times-of-flight. This calibration method gives intrinsically well-behaved results, since nonlinearities (due to extraction delay, desorption velocity, etc.) are properly taken into account in the time-of-flight calculation. The simplex method is compared to curve fitting for the analysis of time-of-flight data, and some significant advantages are demonstrated. Salient features of the method include greatly improved mass extrapolation accuracy, no loss of interpolated calibration accuracy, the ability to obtain an accurate calibration with a minimal number of calibrants, and the ability to extract unknown parameters such as desorption velocities.