Electrospray Ionisation Mass Spectrometry (ES-MS)

Electrospray Ionisation Mass Spectrometry (ES-MS) is a method in which a stream of liquid, containing one or more analytes, is injected via a capillary into the atmospheric pressure ion source of a mass spectrometer. A potential difference is maintained between the end of the capillary and a counter-electrode, causing the formation of microdroplets. In most instrumentation, a drying gas removes excess solvent from the microdroplets, resulting in the creation of multiply-charged molecular ions. Multiply-charging makes the analysis of molecules with molecular weights in excess of 100kDa amenable to instrumentation with scan capabilities up to m/z 4000.

ES-MS may be used in a wide variety of applications throughout biopharmaceutical, pharmaceutical, industrial, environmental and forensic analysis e.g: disulphide bridge analysis, intact molecular weight, analysis of PEG and TWEEN, identification of detergents, detection of lead-replacement additive in fuel etc.

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 mass spectrometry (ES-MS/MS).

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). UV detectors can be used in-line with ES-MS detection to provide methods for components with good chromaphores with poor ionisation efficiency and vice-versa. Both qualitative and quantitative methods can be employed, each providing high sensitivity for the analyte in question.