Ab initio molecular orbital (MO) calculations support the proposal that the key processes in the rearrangement of HOCH2CH2OH•+ and HOCH2CH(CH3)OH•+ (ionized 1,2-ethanediol and 1,2-propanediol) are sequential transfers of a proton and an electron taking place from one partner to the other in ion−dipole complexes rather than prompt hydrogen atom shifts taking place in distonic ions. Although the proposed distonic ions in the alternative mechanism (J. Am. Chem. Soc. 1992, 114, 2027) are thermodynamically remarkably stable species, a surprisingly large barrier exists for their interconversion by way of a 1,4-H atom shift. This large barrier results from significant distortion, from planarity, of the transition state. The rearrangement process of ionized 1,2-ethanediol and 1,2-propanediol can therefore best be described in terms of intramolecular catalysis (proton transport catalysis, Int. J. Mass Spectrom. Ion Processes 1992, 115, 95) in combination with an electron transfer taking place in intermediate ion−dipole complexes.

A novel method for separating ions according to their charge state using a quadrupole time-of-flight mass spectrometer is presented. The benefits of charge state separation are particularly apparent in protein identification applications at low femtomole concentration levels, where in conventional TOF MS spectra peptide ions are often lost in a sea of chemical noise. When doubly and triply charged tryptic peptide ions need to be filtered from singly charged background ions, the latter are suppressed by two to three orders of magnitude, while from 10-50% of multiply charged ions remain. The suppression of chemical noise reduces the need for chromatography and can make this experimental approach the electrospray equivalent of conventional MALDI peptide maps. If unambiguous identification cannot be achieved, MS/MS experiments are performed on the precursor ions identified through charge separation, while the previously described Q2-trapping duty cycle enhancement is tuned for approximately 1.4 of the precursor m/z to enhance intensities of ions with m/z values above that of the precursor. The resulting product ion spectra contain few fragments of impurities and provide quick and unambiguous identification through database search. The multiple charge separation technique requires minimal tuning and may become a useful tool for analysis of complex mixtures.

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This paper demonstrates improved nanoflow LC-MS performance on a QqTOF instrument with the incorporation of a heated nanoflow interface (particle discriminator) and a nebulizer assisted sprayer. It is shown that the nebulizer broadens the usable range of electrospray potentials, simplifying the tuning procedure, particularly for negative mode nanoflow gradients. The improved desolvation capability with the particle discriminator results in signal/noise improvements of approximately 3.5ϫ for negative ion mode samples prepared in predominantly acidified water as well as increased ion current stability. For nanoLC applications, the combined desolvation capabilities of a counter-current gas and heated laminar flow chamber provide reduced background, increased signal stability, reduced background drift, and improved protein sequence coverage when compared with data generated with only a counter-current gas for desolvation. This system is capable of subfemtomole nanoflow LC-MS sensitivity in both positive and negative ion mode across the solvent gradient. and electrospray ionization-mass spectrometry (ESI-MS) has evolved substantially since its initial implementation in the 1980s [1]. Traditional LC systems operated at solvent flow rates that were orders of magnitude higher (hundreds of L/min to mL/min) than those used for mass spectrometry (tens of L/ min), resulting in the need for solvent flow splitters [2]. Some of the subsequent improvements were focused on the use of nebulizer gases [3] and heating [4,5] for stabilization of the electrospray process to accommodate higher LC solvent flows.An alternate approach involves modification of the LC system to accommodate separations within the nanoflow regime [6,7]. Nanoflow LC-MS offers benefits in terms of sensitivity, solvent consumption, and sample consumption when compared with higher flow rate LC-MS, however, it can be much more difficult to operate. Nanoflow sprayers are typically fabricated from tapered fused silica capillary resulting in the need for some type of surface coating [8,9], inserted electrode [10,11], conductive union [6, 12, 13], or dialysis membrane [14] for application of the electrospray potential. Alternatively, sprayers can be fabricated from conductive materials, such as stainless steel, [15], however, tapered stainless steel sprayers are much more difficult to fabricate than fused silica sprayers. An additional benefit associated with fused silica sprayers is that the analytical column may be packed directly into the tapered sprayer, eliminating any post-column dead volume [16,17].A necessary but understated requirement for gradient elution in nanoLC-MS is an electrospray system that is capable of stable operation over a wide range of solvent compositions, particularly for samples containing both hydrophilic and hydrophobic components. Typical nanoflow electrospray systems display good stability for samples consisting of 20 to 100% organic solvent. However, stability can be an issue when running predominantly aqueous solvents because of the h...

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