Routine Part-per-Million Mass Accuracy for High- Mass Ions: Space-Charge Effects in MALDI FT-ICR
M L Easterling1, T H Mize, I J Amster
1Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556.
Analytical Chemistry
|June 14, 2011
Summary
Ion space charge significantly impacts mass accuracy in Fourier transform ion cyclotron resonance mass spectrometry. Accounting for ion population corrects mass errors, improving precision for complex samples like polymers.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
- Spectrometry
Background:
- Space charge effects in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) can lead to significant mass measurement errors.
- Accurate mass determination is crucial for identifying and characterizing analytes, especially in complex mixtures.
Purpose of the Study:
- To investigate and quantify the effect of ion space charge on mass accuracy in FT-ICR MS.
- To develop and validate methods for correcting space-charge-induced mass errors.
Main Methods:
- Utilized matrix-assisted laser desorption/ionization (MALDI) to generate high-molecular-weight polymer ions.
- Employed ion remeasurement and suspended trapping techniques to control ion density.
- Correlated observed cyclotron frequency with ion population.
- Developed calibration strategies based on total ion intensity.
Main Results:
- A linear correlation was observed between cyclotron frequency and ion population.
- Uncorrected mass spectra showed errors exceeding 100 ppm due to ion number.
- Achieved mass accuracy of 0.07 ppm for insulin B-chain using polymer calibrants and intensity matching.
- A proposed calibration procedure yielded 2.0 ppm accuracy for insulin B-chain.
Conclusions:
- Ion space charge is a critical factor affecting mass accuracy in FT-ICR MS.
- Methods accounting for ion population and total ion intensity effectively correct for space-charge-induced errors.
- These corrections are particularly important for complex samples with wide mass distributions.
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