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Analyses of cryogenic samples using ion-induced desorption and multiphoton resonance ionization
M H Ervin1, M C Wood, N Winograd
1152 Davey Laboratory, Department of Chemistry, Pennsylvania State University, University Park 16802.
Analytical Chemistry
|February 15, 1993
Summary
This study characterizes frozen aqueous solutions using ion-beam desorption and multiphoton resonance ionization. This method accurately quanties tryptophan concentration in biological matrices, achieving a detection limit of 2 x 10(-6) M.
Area of Science:
- Analytical Chemistry
- Surface Science
- Biophysics
Background:
- Frozen aqueous solutions serve as crucial models for biological matrices.
- Characterizing molecular concentrations in these matrices is vital for biological and chemical analysis.
- Existing methods may have limitations in sensitivity or applicability to frozen samples.
Purpose of the Study:
- To develop and validate a method for characterizing frozen aqueous solutions.
- To assess the utility of ion-beam-induced desorption with multiphoton resonance ionization detection (IBID-MPI) for quantifying molecules in frozen matrices.
- To establish the detection limits and concentration dependence of the method for tryptophan.
Main Methods:
- Utilized ion-beam-induced desorption (IBID) to desorb neutral molecules from frozen aqueous solutions.
- Employed multiphoton resonance ionization (MPI) detection for sensitive and selective analysis of desorbed molecules.
- Analyzed millimolar tryptophan/H2O solutions and compared results to tryptophan on silicon wafers.
- Used 4,4'-biphenyldiol as an internal standard to determine concentration linearity.
Main Results:
- The time-of-flight mass spectrum for frozen tryptophan/H2O solutions closely matched that of tryptophan on a silicon wafer.
- Demonstrated a linear relationship between the tryptophan signal and its concentration in frozen solutions.
- Achieved a detection limit of 2 x 10(-6) M, corresponding to approximately 4 x 10(6) molecules per sampled layer.
- Observed an exponential decay in signal with increasing primary ion dose due to radiation damage.
Conclusions:
- IBID-MPI is a highly effective technique for characterizing frozen aqueous solutions, including biological models.
- The method offers high sensitivity and quantitative accuracy for molecular analysis in frozen matrices.
- Further optimization may be needed to mitigate signal decay caused by primary ion dose accumulation.