DETERMINATION OF HIGH-ENERGY FRAGMENTATION OF PROTONATED PEPTIDES USING A BEQQ HYBRID MASS-SPECTROMETER

A hybrid tandem instrument of BEqQ geometry was used to determine high -energy decomposition of protonated peptides, such as side-chain fragm entation yielding d(n) and w(n) ions. The transmission through both E and Q of such product ions, formed in the second field-free region, pe rmits improved mass resolution and confident mass assignment. The expe rimental technique may involve synchronous scanning of E and Q, or, fo r the purpose of identification of specific products, limited-range sc anning of either E or Q with the other analyzer fixed. These technique s are not equivalent, with respect to product ion transmission, to the double focusing of product ions achieved with four-sector instruments but nevertheless represent a critical improvement over conventional m ass-analyzed ion kinetic energy spectrometry analyses. Fragmentation o f protonated peptides occurring in the second field-free region inside and outside the collision cell were distinguished by floating the col lision cell above ground potential. Mass filtering using Q confirmed t he mass assignments. The data indicate that product ions resulting fro m spontaneous decomposition are in some instances quantitatively more significant than those resulting from high-energy collisional activati on. Furthermore, the differentiation of the products of low- and high- energy processes should facilitate spectral interpretation.