Negative‐ion electrospray mass spectra of peptides derivatized with 4‐aminonaphthalenesulphonic acid

Abstract

The detection limits of a series of small peptides derivatized with 4-aminonaphthalenesulphonic acid have been determined using a magnetic sector mass spectrometer operated in the negative-ion mode. The instrument (Autospec-QFPD) is equipped with an electrospray ion source and both array and point detectors. Detection limits when using the array detector were on the sub-femtomole level at a mass resolution of 2000 (full width half maximum height). Cone-voltage and linked-scan collision-induced dissociation spectra were recorded using both the array and point detectors. When using the array detector, amino acid sequence information could be obtained from as little as 50 fmol of sample consumed.The development of the electrospray (ES) ion source' has had a revolutionary impact on the study of proteins and peptides by mass spectrometry. Up to the early 1990s most electrospray studies had been performed on quadrupole mass spectrometers.* However, magnetic sector instruments are now being equipped with reliable electrospray source^.^ Difficulties have arisen in the interfacing of ES sources to magnetic sector instruments because of the requirements of a high source voltage and a high vacuum. These problems have now been largely overcome with the use of effective pumping and with the advent of high-transmission ion optics within the ion transport r e g i~n .~As new types of ion sources have been developed in the 1980s and 1990s, different methods for ion detection have also been investigated. The array detector is now being used on modern magnetic sector mass spectrometers. These detectors provide a great increase in sensitivity compared with point photo-multiplier or electron-multiplier detectors.Although an array detector will provide an increase in sensitivity over a point detector, this advantage will not be seen when ions are generated by sputtering methods such as static fast-atom (or ion) bombardment (FAB), as both the intensity of the ion of interest and of the chemical background are increased. To obtain the best results with an array detector it is necessary to employ an ion source which does not give a copious amount of chemical noise. Impressive results have been 'obtained by Kenny and Ornaldo' using continuous flow-FAB (CF-FAB) on a four-sector instrument. On two-sector and hybrid instruments, the electrospray ion source may be more appropriate as it provides less background chemical noise than CF-FAB .Recent work in this laboratory has shown the benefit of derivatizing lipids with aminosulphonic acids for analysis by negative-ion FAB mass s p e c t r~m e t r y .~~ Series of bile acids, fatty acids and hydroxy acids have been derivatized with aminosulphonic acids in a peptide linkage at the carboxylic acid group. The effect is to increase the yield of pseudomolecular [M -HIions. Furthermore, high translational energy collisioninduced dissociation (CID) reactions of sulphonated lipids result in charge-remote fragmentations (CRF).

Acceleration and Improvement of Protein Identification by Mass Spectrometry

“…The main advantage of such modification is the improvement of negative mode detection, which is increased 5to 50-fold (Griffiths, Lindh, Bergman, & Sjövall, 1995). (Keough et al, 1999b), ©1999) 5.2.6.3.…”

On‐target sample preparation of 4‐sulfophenyl isothiocyanate‐derivatized peptides using AnchorChip Targets

“…Another early method developed by Lindh and Griffiths explores coupling sulfonic acid to the C ‐terminal of the peptides. This resulted in fragmentation primarily at the peptide backbone in negative mode when low‐energy collision using helium as collision gas was applied 21–23…”

Electrospray tandem mass spectrometric study of alkyl 1‐methylpyridinium ether derivatives of alcohols

“…In general, analytes that are not ionized by the time they exit the ES emitter will not be detected by this technique. Chemical derivatization is an established method for the transformation of such analytes into compounds that are amenable to ES‐MS analysis 3–31. The spectra produced by these and other molecules in ES‐MS are usually very simple.…”