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The main difference between vacuum MALDI and AP-MALDI is the pressure in which the ions are created. In vacuum MALDI, ions are typically produced at 10 mTorr or less while in AP-MALDI ions are formed in atmospheric pressure.
An interesting example of this is studying the interactions between enzymes and drugs which are inhibitors of the enzyme. [71] [72] [73] Competition studies between STAT6 and inhibitors [73] [74] [75] have used ESI as a way to screen for potential new drug candidates. Electrospray ionization can even be used for studying protein complexes >1 ...
The experimental settings involved in the communication between the sampling stage, mass spectrometer and laser desorption, such as stage height, ESI-Spot distance and laser repetition rate, have undergone progressive optimization by several design of experiments (DOE).
It can also be used to localize proteins to the various organelles, and determine the interactions between different proteins as well as with membrane lipids. [1] [2] The two primary methods used for the ionization of protein in mass spectrometry are electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI).
Laser ablation electrospray ionization (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary electrospray ionization (ESI) process. The mid-IR laser is used to generate gas phase particles which are then ionized through interactions with charged droplets ...
A typical workflow of a peptide mass fingerprinting experiment. Peptide mass fingerprinting (PMF), also known as protein fingerprinting, is an analytical technique for protein identification in which the unknown protein of interest is first cleaved into smaller peptides, whose absolute masses can be accurately measured with a mass spectrometer such as MALDI-TOF or ESI-TOF. [1]
In this technique, it utilizes Infrared laser ionization to excite the sample molecules to allow for the desorbed ions to be ready for MS analysis. The geometry of the source and the distance between the ESI and matrix will have and effect on the efficiency of the sample compound. [16] This technique can also be used with aqueous samples as well.
Radical cations can also be observed in a FAB spectrum in rare cases. FAB was designed as an improved version of SIMS that allowed for the primary beam to no longer cause damaging effects to the sample. The major difference between the two techniques is the difference in the nature of the primary beam used; ions vs atoms. [8]