The curved field reflectron has been in existence for nearly two decades since it was introduced by Cotter and Cornish. For several years the CFR was used in the only commercially available instrument capable of MALDI TOF MS/MS without scanning the reflectron. Seamless PSD provided advantages in terms of both sensitivity and speed of acquisition. However, the key advantage of the CFR over conventional linear field reflectrons, even those used in TOF/TOF instruments has been the ability to produce MS/MS at the full extraction energy. This is because there is no need with the CFR to re-accelerate the ions after the first TOF. So that, not only is very high sensitivity achieved for MS/MS but also that true high-energy CID is possible with lab collision energies of 20keV or more.

However, even when used in MALDI TOF instruments with in excess of 20,000 mass resolutions for MS, the mass resolution using the CFR for MS/MS was limited to isotopic resolution up to about 1000 Da. This has been known for a long time to be due to the increase in the laser intensity required to produce the meta-stable ions required for MS/MS (even with high-energy CID) which is much higher than the threshold for MALDI TOF MS. However, until recently, the effect had not been understood or quantified. More importantly, the reduced mass resolution has meant that the CFR instruments were not able to match the ultimate performance of other TOF/TOF instruments.

In this paper, we present the basic theory behind Axial Spatial Distribution Focussing (ASDF) as well as its applications for various structural elucidations and applications problem. Lipids fragmentations data showing C-C backbone fragmentation as well as high energy tandem Mass spectra of Peptides allowing differentiation of isomeric species will be presented. With the technique of Axial Spatial Distribution Focussing in combination with the Curved-Field Reflectron, fragment mass resolutions in excess of 10,000 can be achieved for MS/MS of meta-stable ions and CID at lab energy of 20keV.  By using ASDF, the Curved-Field Reflectron is again capable of defining the state of the art for MALDI TOF-MS/MS and can really be said to have come of age.