Bio-)nanoparticle analysis employing a nano-electrospray gas-phase electrophoretic mobility molecular analyzer (native nES GEMMA) also known as nES differential mobility analyzer (nES DMA) is based on surface-dry analyte separation at ambient pressure. Based on electrophoretic principles, single-charged nanoparticles are separated according to their electrophoretic mobility diameter (EMD) corresponding to the particle size for spherical analytes. Subsequently, it is possible to correlate the (bio-)nanoparticle EMDs to their molecular weight (M W) yielding a corresponding fitted curve for an investigated analyte class. Based on such a correlation, (bio-)nanoparticle M W determination via its EMD within one analyte class is possible. Turning our attention to icosahedral, non-enveloped virus-like particles (VLPs), proteinaceous shells, we set up an EMD/M W correlation. We employed native electrospray ionization mass spectrometry (native ESI MS) to obtain M W values of investigated analytes, where possible, after extensive purification. We experienced difficulties in native ESI MS with time-of-flight (ToF) detection to determine M W due to sample inherent characteristics, which was not the case for charge detection (CDMS). nES GEMMA exceeds CDMS in speed of analysis and is likewise less dependent on sample purity and homogeneity. Hence, gas-phase electrophoresis yields calculated M W values in good approximation even when charge resolution was not obtained in native ESI ToF MS. Therefore, both methods-native nES GEMMA-based M W determination via an analyte class inherent EMD/M W correlation and native ESI MS-in the end relate (bio-)nanoparticle M W values. However, they differ significantly in, e.g., ease of instrument operation, sample and analyte handling, or costs of instrumentation.
MALDI mass spectrometry
imaging (MALDI MSI) is a powerful analytical
method for achieving 2D localization of compounds from thin sections
of typically but not exclusively biological samples. The dynamically
harmonized ICR cell (ParaCell) was recently introduced to achieve
extreme spectral resolution capable of providing the isotopic fine
structure of ions detected in complex samples. The latest improvement
in the ICR technology also includes 2ω detection, which significantly
reduces the transient time while preserving the nominal mass resolving
power of the ICR cell. High-resolution MS images acquired on FT-ICR
instruments equipped with 7T and 9.4T superconducting magnets and
the dynamically harmonized ICR cell operating at suboptimal parameters
suffered severely from the pixel-to-pixel shifting of
m
/
z
peaks due to space-charge effects. The resulting
profile average mass spectra have depreciated mass measurement accuracy
and mass resolving power under the instrument specifications that
affect the confidence level of the identified ions. Here, we propose
an analytical workflow based on the monitoring of the total ion current
to restrain the pixel-to-pixel
m
/
z
shift. Adjustment of the laser parameters is proposed to maintain
high spectral resolution and mass accuracy measurement within the
instrument specifications during MSI analyses. The optimized method
has been successfully employed in replicates to perform high-quality
MALDI MS images at resolving power (FWHM) above 1,000,000 in the lipid
mass range across the whole image for superconducting magnets of 7T
and 9.4T using 1 and 2ω detection. Our data also compare favorably
with MALDI MSI experiments performed on higher-magnetic-field superconducting
magnets, including the 21T MALDI FT-ICR prototype instrument of the
NHMFL group at Tallahassee, Florida.
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