Electrospray Ionisation with Tandem Mass spectrometry (ES-MS/MS)
ES-MS is a technique which, in most cases, provides a molecular ion species with little or no fragmentation, due to the low energy imparted during ionisation. Structurally rich information can be obtained, however, by using tandem MS, which uses collisionally activated decomposition (CAD) of molecular species with an inert gas such as Argon. In the MS/MS experiment, performed on a triple quadrupole, hybrid quadrupole-time of flight or magnetic sector instrument, a single molecular ion is selected using the first mass analyser and is passed through a collision cell where fragment ions are produced. The fragment ions generated are then separated by a second mass analyser and detected. The structural information obtained is highly selective and specific to each unique molecular ion species selected. There are many variations of the MS/MS experiment which can be tailored to meet specific analytical requirements.
ES-MS/MS may be used in a wide variety of applications throughout biopharmaceutical, pharmaceutical, industrial, environmental and forensic analysis e.g.: disulfide bridge analysis, accurate mass analysis, peptide mapping, proteomics, oligonucleotide sequencing, etc.
The use of volatile solvents and buffers in HPLC provides a powerful separation technique which is compatible with ES-MS (LC-MS) and ES-MS/MS (LC-MS/MS). The use of LC-ES-MS/MS can often offer significant improvement in selectivity, specificity and sensitivity during quantitative analyses over similar LC-ES-MS applications.