11 research outputs found
New Ionization Method for Analysis on Atmospheric Pressure Ionization Mass Spectrometers Requiring Only Vacuum and Matrix Assistance
Matrix assisted ionization <i>vacuum</i> (MAIV)
is a
new ionization method that does not require high voltages, a laser
beam, or applied heat and depends only the proper matrix, 3-nitrobenzonitrile
(3-NBN), and the vacuum of the mass spectrometer to initiate ionization.
Analyte ions of volatile as well as nonvolatile compounds are formed
by simply exposing the matrix–analyte to the vacuum of a mass
spectrometer. The reduced pressure at the inlet of an atmospheric
pressure ionization mass spectrometer suffices to produce analyte
ions, but unlike the previously reported matrix assisted ionization <i>inlet</i> method, with MAIV, heating the inlet is not necessary.
Singly and multiply charged ions are formed similar to electrospray
ionization but from a surface. Mass spectrometers in which a heated
inlet tube is not available can be used for ionization using the 3-NBN
matrix. We demonstrate rapid, high-sensitivity analyses of drugs,
peptides, and proteins in the low femtomole range. The potential for
high-throughput analyses is shown using multiwell plates and paper
strips
Laserspray Ionization Imaging of Multiply Charged Ions Using a Commercial Vacuum MALDI Ion Source
This is the first report of imaging mass spectrometry
(MS) from
multiply charged ions at vacuum. Laserspray ionization (LSI) was recently
extended to applications at vacuum producing electrospray ionization-like
multiply charged ions directly from surfaces using a commercial intermediate
pressure matrix-assisted laser desorption/ionization ion mobility
spectrometry (IMS) MS instrument. Here, we developed a strategy to
image multiply charged peptide ions. This is achieved by the use of
2-nitrophloroglucinol as matrix for spray deposition onto the tissue
section and implementation of “soft” acquisition conditions
including lower laser power and ion accelerating voltages similar
to electrospray ionization-like conditions. Sufficient ion abundance
is generated by the vacuum LSI method to employ IMS separation in
imaging multiply charged ions obtained on a commercial mass spectrometer
ion source without physical instrument modifications using the laser
in the commercially available reflection geometry alignment. IMS gas-phase
separation reduces the complexity of the ion signal from the tissue,
especially for multiply charged relative to abundant singly charged
ions from tissue lipids. We show examples of LSI tissue imaging from
charge state +2 of three endogenous peptides consisting of between
1 and 16 amino acid residues from the acetylated <i>N</i>-terminal end of myelin basic protein: mass-to-charge (<i>m</i>/<i>z</i>) 795.81 (+2) molecular weight (MW) 1589.6, <i>m</i>/<i>z</i> 831.35 (+2) MW 1660.7, and <i>m</i>/<i>z</i> 917.40 (+2) MW 1832.8
Transmission Geometry Laserspray Ionization <i>Vacuum</i> Using an Atmospheric Pressure Inlet
This represents the first report
of laserspray ionization <i>vacuum</i> (LSIV) with operation
directly from atmospheric pressure
for use in mass spectrometry. Two different types of electrospray
ionization source inlets were converted to LSIV sources by equipping
the entrance of the atmospheric pressure inlet aperture with a customized
cone that is sealed with a removable glass plate holding the matrix/analyte
sample. A laser aligned in transmission geometry (at 180° relative
to the inlet) ablates the matrix/analyte sample deposited on the vacuum
side of the glass slide. Laser ablation from vacuum requires lower
inlet temperature relative to laser ablation at atmospheric pressure.
However, higher inlet temperature is required for high-mass analytes,
for example, α-chymotrypsinogen (25.6 kDa). Labile compounds
such as gangliosides and cardiolipins are detected in the negative
ion mode directly from mouse brain tissue as intact doubly deprotonated
ions. Multiple charging enhances the ion mobility spectrometry separation
of ions derived from complex tissue samples