Equipment

Bruker Daltonics Esquire 3000plus
Harvard Apparatus 11plus Syringe Pump
Domnick Hunter Nitrox UHPLMCS18 Nitrogen Generator

Method overview

In general, with the help of mass spectrometry it is possible to identify (multiply) charged compounds by the detection of mass-to-charge ratios. Furthermore, with isolation and fragmentation experiments (MSⁿ) structural informations of unknown compounds can be obtained.

The Bruker Esquire 3000plus mass spectrometer uses electrospray ionisation (ESI) to generate charged molecules. The mass spectrometer is able to detect mass-to-charge ratios in the range of 50 to 6000.

Benefits of the ESI method

•  Soft ionisation process so intact molecular ions are observed (no fragmentation)
• Good for charged, polar or basic compounds
• Can be applied in positive (formation of positively charged ions) or negative ion mode (generation of negatively charged species)
• ESI allows production of multiply charged ions. This results in the ability of analyzing very high molecular weight species (mostly applies to biologically relevant compounds like proteins)
• ESI is an atmospheric pressure process which makes it easy to use and easy to interface with HPLC separation techniques
• Compatible with MS/MS methods

Limitations

• ESI is not good for compounds (usually non-polar) that can not be easily ionised by forming adducts with protons or cations like Na⁺ or K⁺ in positive mode or by deprotonation in negative mode
• ESI is very sensitive to contaminants such as alkali metals or basic compounds