A NOVEL GEOMETRY MASS-SPECTROMETER, THE Q-TOF, FOR LOW-FEMTOMOLE ATTOMOLE-RANGE BIOPOLYMER SEQUENCING/

Ultra-high-sensitivity. biopolymer sequencing is a goal in many fields of molecular biology, and collisionally activated decomposition elect rospray mass spectrometry (CAD ES MS/MS) using a triple quadrupole mas s spectrometer has become a method of choice for work in the high- to mid-femtomole range. However, when the detection of ions becomes stati stical, as it may in that range, the mass assignment of fragment ions is inaccurate and either sequencing becomes impossible or ambiguities result due, for example, to the closeness in amino acid residue masses (I/L, N or K/Q, E). Some ambiguities may be resolved by synthesizing possible sequences, but this is unsatisfactory. In considering the lim itations of triple quadrupole MS/MS with respect to scanning ion detec tion, resolution, transmission, and mass accuracy, we reasoned that a novel geometry quadrupole orthogonal acceleration time-of-flight (Q-TO F) instrument would have special merit for ultra-high-sensitivity MS/M S sequencing, and suggested its construction for this purpose some thr ee years ago. A prototype Q-TOF has now been built by Micromass [Morri s et al. (1996), Rapid Commun. Mass Spectrom. 10, 889-896], and in the first research on the instrument, including MHC antigen and filarial nematode glycoprotein studies, we demonstrate low-femtomole- and attom ole-range sequencing with mass accuracy of better than 0.1 Da througho ut the daughter-ion spectrum, thus removing sequencing ambiguities in some of the most challenging work demanding the highest sensitivity.