A new electrostatic transfer line for improved transmission in Fourier transform laser microprobe mass spectrometry with external ion source

The efficient extraction and transfer of ions from an external ion source o utside the magnet and their injection through the inhomogeneous fringing fi eld becomes a key factor in the micro-analytical application of Fourier tra nsform mass spectrometry (FTMS) instruments with an external ion source, Th is paper reports on a new ion transfer line with static electrical fields f or a source at a distance of 131 cm from the cylindrical ion cyclotron reso nance OCR) "Infinity" cell in an unshielded 4.7 Tesla superconducting magne t. Basically, ions are accelerated to 2-3 kV, transported through a time-of -flight (TOF) system and decelerated at the entrance of the magnet. The siz e of the system, the magnetic stray field and the significant electrical fi eld gradients require careful optimisation of the simulations with the SIMI ON software, According to our calculations, the new ion transfer line shoul d allow transport and trapping of ions initially emitted with an angle of u p to 35 degrees with the normal, as opposed to 5 degrees with the former co mmercial transfer line with improved cylindrical front optics. The design h as been experimentally verified using focused laser desorption/ionisation o f solids. The data on reference compounds have demonstrated that the sensit ivity with the new transfer line increases by a factor of 10, A substantial gain of sensitivity is also expected for other ionisation methods producin g ions with a more isotropic angular emission than focused laser irradiatio n. The new ion optics are fully compatible with the existing hardware so th at conversion becomes a minor operation.