ABSTRACT
Ultra-high-sensitivity biopolymer sequencing is a goal in many fields of molecular biology, and cotlisionally activated decomposition electrospray mass spectrometry (CAD ES MS/MS) using a triple-quadmpole mass spectrometer has become a method of choice for work in the high to mid femtomole range. However, when the detection of ions becomes statistical, as it may in that range, the mass assignment of fragment ions is inaccurate and either sequencing becomes impossible or ambiguities may result, due, for example, to the small differences in amino acid residue masses (IIL,N or K/Q,E). Some ambiguities may be resolved by synthesizing possible sequences, but this is time-consuming and costly. In considering the limitations of triple-quadmpole MS/MS with respect to scanning ion detection, resolution, transmission, and mass accuracy, we reasoned that a novel geometry quadmpole orthogonal acceleration time-offlight (Q-TOF) instmment would have special merit for ultra-high-sensitivity MS/MS sequencing, and suggested its construction for this purpose in 1994. In the first research on this new instrument, including major histocompatibility complex (MHC) antigen and filarial nematode glycoprotein studies. low femtomole and attomole range sequencing has been demonstrated [I ] with mass accuracy of better than 0.1 Da throughout the daughter ion spectmm, thus removing sequencing ambiguities in some of the most challenging work demanding the highest sensitivity.
