04-05-2012, 05:19 PM
Automation of Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Using Fuzzy Logic Feedback Control
Automation of Matrix-Assisted Laser Desorption Ionization Mass Spectrometry_01.pdf (Size: 383.34 KB / Downloads: 40)
EXPERIMENTAL SECTION
Sample Preparation. Matrix surfaces were made by fast
evaporation on the MALDI probe tip of 0.2-0.3 íL of a saturated
solution of 4-hydroxy-R-cyanocinnamic acid (4HCCA, Sigma, St.
Louis, MO) in acetone.20,21 Some samples were analyzed using
nitrocellulose as an added component of the thin matrix films.22,23
Dried peptide samples were redissolved in 20-30 íL of 1% formic
acid/10% acetonitrile, and 0.5 íL of the peptide solution was
deposited on top of the fast-evaporation matrix film. The liquid
was left to evaporate at ambient temperature, and the dried sample
deposit was then washed with pure water or 1% formic acid prior
to mass analysis. Dried-droplet sample deposits were prepared
by mixing 0.5 íL of peptide solution with 4.5 íL of matrix solution
(4HCCA in 5% formic acid/acetonitrile, 2:1 v/v) and depositing
0.5 íL of the mixture on the MALDI probe tip. Dried sample
deposits were rinsed with pure water or 1% formic acid prior to
mass analysis.
RESULTS AND DISCUSSION
Implementation of Fuzzy Logic Control. The important
model variables monitored in MALDI are ion intensity and peak
resolution. Based on these values, the operator continuously
changes the laser fluence to optimize signal-to-noise ratio without
compromising peak resolution. The decision process used by a
human operator for determining the laser fluence during MALDI
data acquisition can be simply described in everyday language
by a few rules with intensity and resolution as input variables and
the fluence change as the output variable.
CONCLUSION AND PROSPECTS
We have demonstrated that automation of MALDI-MS for the
acquisition of mass spectra of biomolecules is feasible and
relatively simple when using a fuzzy logic-based feedback control
system. The performance of the automated MALDI-TOF mass
spectrometer is comparable to that of a skilled human operator.
During analysis of hundreds of samples, including synthetic
peptides, oligonucleotides, HPLC fractionated peptides, and peptide
mixtures produced by in-gel digestion of proteins, no
problems with instability in the form of major fluctuations or
drifting of the fuzzy logic control system have been encountered.