1 instrumentation
1.1 laser
1.2 time of flight
1.3 atmospheric pressure
instrumentation
diagram of maldi tof instrument. sample matrix ionized radiant energy ejected surface. sample travels mass analyzer , substantially detected.
there several variations of maldi technology , comparable instruments today produced different purposes. more academic , analytical, more industrial , high throughput. ms field has expanded requiring ultrahigh resolution mass spectrometry such ft-icr instruments more high-throughput instruments. many maldi ms instruments can bought interchangeable ionization source (electrospray ionization, maldi, atmospheric pressure ionization, etc.) technologies overlap , many times soft ionization method potentially used. more variations of soft ionization methods go soft laser desorption or ion source.
laser
maldi techniques typically employ use of uv lasers such nitrogen lasers (337 nm) , frequency-tripled , quadrupled nd:yag lasers (355 nm , 266 nm respectively).
infrared laser wavelengths used infrared maldi include 2.94 µm er:yag laser, mid-ir optical parametric oscillator, , 10.6 µm carbon dioxide laser. although not common, infrared lasers used due softer mode of ionization. ir-maldi has advantage of greater material removal (useful biological samples), less low-mass interferences, , compatibility other matrix-free laser desorption mass spectrometry methods.
time of flight
sample target maldi mass spectrometer
the type of mass spectrometer used maldi tof (time-of-flight mass spectrometer), due large mass range. tof measurement procedure ideally suited maldi ionization process since pulsed laser takes individual shots rather working in continuous operation. maldi-tof instrument or reflectron equipped ion mirror reflects ions using electric field, thereby doubling ion flight path , increasing resolution. today, commercial reflectron tof instruments reach resolving power m/Δm of above 20,000 fwhm (full-width half-maximum, Δm defined peak width @ 50% of peak height).
maldi has been coupled ims-tof ms identify phosphorylated , non-phosphorylated peptides.
maldi-ft-icr ms has been demonstrated useful technique high resolution maldi-ms measurements desired.
atmospheric pressure
atmospheric pressure (ap) matrix-assisted laser desorption/ionization (maldi) ionization technique (ion source) in contrast vacuum maldi operates @ normal atmospheric environment. main difference between vacuum maldi , ap-maldi pressure in ions created. in vacuum maldi, ions typically produced @ 10 mtorr or less while in ap-maldi ions formed in atmospheric pressure. in past main disadvantage of ap maldi technique compared conventional vacuum maldi has been limited sensitivity; however, ions can transferred mass spectrometer high efficiency , attomole detection limits have been reported. ap-maldi used in mass spectrometry (ms) in variety of applications ranging proteomics drug discovery. popular topics addressed ap-maldi mass spectrometry include: proteomics; mass analysis of dna, rna, pna, lipids, oligosaccharides, phosphopeptides, bacteria, small molecules , synthetic polymers, similar applications available vacuum maldi instruments. ap-maldi ion source coupled ion trap mass spectrometer or other ms system equipped esi (electrospray ionization) or nanoesi source.
Comments
Post a Comment