Accurate linked scans based on digital real time mass linearization and function generation

Abstract

A new, commercially available digital linked scan unit mass display/macker is presented operating in real time in a mass range of 0.0 to 1638.3 u without the need for a data system. The prerequkites and limitations of successful linked scans with their consequences for the new design are discussed. Examples give evidence of the need for increased accuracy. INTRODUCI'ION ~~Linked scans and mapping techniques are well-known means of establishing the fragmentation pathway of ions outside the ion source. Parent ion search experiments at a given daughter ion mass m2 and daughter ion search experiments at a given parent ion mass ml have both been successfully used in mixture analysis and structure elucidation.' More recently, constant neutral loss scans have been introduced. They allow the search for ions fragmentating by loss of a given uncharged mass Am.2*3 These scans are especially useful in mixture analysis when looking for ions with identical functional group^.^ Thus, linked scans on double focusing sector type mass spectrometers now offer possibilities of using MS/MS techniques, which are typically performed by the more complex triple stage instruments. Limitations exist however, arising mainly from the parameters varied by the scans, the geometry of the mass spectrometer and the possible occurrence of artefact peaks.The mass number of singly charged ions rn* transmitted in standard in-focus spectra ( E = E,, V = V,) defines a convenient measure for the magnetic field B.If exclusively singly charged ions are assumed, the daughter ions of dissociations outside the ion source will only be transmitted by the magnetic sector at m* = m22/m1. Examples are the well-known metastable peaks arising from dissociations within the field free region (FFR) preceding the magnetic field. They are observed in single focusing and conventional geometry double focusing mass spectroscopy. In general m* is not sufficient to deduce m,, m2 and Am. The observation of better defined diffuse peaks is, however, possible with double focusing instruments, preferably by linked scans varying B and the electric sector voltage E simultaneously, according to suitable scan laws. The acceleration voltage V, thereby remains constant in order to avoid detuning of the ion source and unnecessary limitation of the range of observable m a~s e s .~ Daughter ions m2 arising from dissociations in the first field free region (FFR1) in between the accelerating field (ACCF) and the first sector field and, on instruments of reversed geometry, from dissociations within WR2, the region in between the two sector fields, are thereby detected. These ions are transmitted by the electrostatic analyser (ESA) with reduced E at E/E, = mJm, due to the loss of mass and hence of energy. The two instrument-independent quantities m" and E/E, characterize the location of diffuse peaks and allow the determination of m,, m2 and Am. The preselection of any of these three masses restricts the location of expected diffuse peaks to a corresponding line on the m*-E/Eo plane (Fig. 1). ...

Profiling and quantification of biogenic amines in wine by constant B2E linked scan mass spectrometry

“…In addition interfering signals caused by fragmentations in the other field free region are much less common, specially in the higher mass range. 12 The peak width and the apparent resolution can be chosen by varying the resolution of the magnetic sector, resulting in higher sensitivity at lower r e s~l u t i o n .~ Figure 1 presents the example of dansyl-ethanolamide. The CID-B2E scan of the fragment at m / z 169 shows an ion at m / z 294 as the main precursor, which is the molecular ion of the dansylamide.…”