The implementation and application of precursor‐ion scanning using a four‐sector instrument

Abstract

Precursor-ion scanning, in which all ions that fragment to form a selected product ion are detected, has been implemented on a four-sector instrument. The various experimental parameters associated with the experiment i.e., precursor mass range, product and precursor ion resolution, collision energy and mass-measurement accuracy have been established via a series of experiments. Brief examples of the use of the technique in the characterization of synthetic polymers, quaternary salts and peptides are described together with the analysis of a mixture of phthalate esters.One of the major uses of tandem mass spectrometry (MS/MS) has been in the analysis of complex mixtures' and in structural studies. By far the most utilized mode of MS/MS analysis has been product-ion scanning, but use has also been made of precursor-ion scans in which, for example, phthalate esters are characterized by the observation of m/z 149 which is a characteristic ion in the product-ion spectra of this compound c l a s~.~-~ By using a precursor-ion scan of m/z 149, the identities of various phthalate esters in a complex mixture have been established.Precursor-ion scans may be easily implemented on a triple-quadrupole instrument with unit mass resolution of both precursor ions and product ions being obtained. They have also been implemented on various hybrid instruments in which a quadrupole collision cell and analytical quadrupole follow a double-focusing instrument. Here unit mass resolution of the selected product ion can be combined with medium mass resolution (a few thousand) of the precursor ions. Both triplequadrupole and hybrid instruments have access only to low-energy collision regimes. Precursor-ion scans can also be performed on a two-sector instrument using a linked scan at constant B 2 / E which gives a precursorion resolution of only a few hundred at best' but has the advantage of kilovolt collision energies.The use of multi-sector instruments has been limited to product-ion spectra only, despite the potential advantages of such instruments in terms of accessible mass range, the possibility of using kilovolt collision energies, and obtainable resolution. Precursor scans on a four-sector instrument may be carried out in two ways. The first is to scan both magnets simultaneously in opposite directions, but the difficulty of maintaining the correct relationship between B, and B2 has discouraged this approach in practice.The second approach is to use an electrically floated collision cell and make use of the energy transmission window of MS2 to transmit simultaneously a product mass with a range of energies determined by the masses of its precursors.* Author to whom correspondence should be addressedWe have been able to make use of the exceptionally wide energy acceptance of MS2 on the ZAB-T tandem instrument (VG Analytical Ltd, Manchester, UK) to implement precursor-ion scanning in this way, with collision energies as high as 2 keV. Examples of data which establish the performance of this approach are presented here. EXPERIMENTALT...

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Linked‐scan techniques for MS/MS using tandem‐in‐space instruments

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