Electrospray mass spectrum structural information from

MS-MS is a term that covers a number of techniques in which two stages of mass spectrometry are used to investigate the relationship between ions found in a mass spectrum. In particular, the product-ion scan is used to derive structural information from a molecular ion generated by a soft ionization technique such as electrospray and, as such, is an alternative to CVF. The advantage of the product-ion scan over CVF is that it allows a specific ion to be selected and its fragmentation to be studied in isolation, while CVF bring about the fragmentation of all species in the ion source and this may hinder interpretation of the data obtained. 

More extensive structural information is obtained when using MS-MS, where information on the peptide sequence can be extracted from the fragmentation pattern. So far, CE-MS-MS has predominantly been performed with electrospray ionization (ESI)-triple quadrupole and ESI-ion trap instruments, as reviewed in Ref. 13. The advent of ESI-TOF and ESI-quadru-pole-TOF instruments is believed to have a strong impact on CE-MS. TOF instruments require an extremely short time to produce a full mass spectrum and are especially attractive as a detection device for a separation technique producing sharp peaks, as illustrated by the separation of three enkephalins in a time window of 6 s with detection by means of ESI-TOF [14],... 

Electrospray ionisation (ESI) is a technique that takes place at atmospheric pressure and is considered to be a soft ionisation process. It is very useful for liquids. Unlike hard processes, the molecule is not normally fragmented and so the resulting mass spectrum is much simpler, the principal peak of which will be the pseudo-molecular ion, i.e. a pro-tonated or sodiated peak. It is therefore much easier to decipher the molecular weight of a compound from an ESI source but there is less structural information given about the molecule, if any. 

---