Biomolecule mass measurement
The masses of molecules of interest (proteins/peptides, oligosaccharides, lipids or nucleic acids) can be determined with high accuracy using mass spectrometry. The size of a known protein or peptide can be confirmed or the extent of its modification (proteolytic, post-translational or chemical) determined. Mass profiles of biological fluids can be made.
The sample should be in soluble form and free of detergents. Desalting by reversed phase chromatography (on-line or off-line) is often necessary.
ESI-MS (generates multiple charge states of proteins)
LTQ Orbitrap XL ETD (Thermo Fisher Scientific)
- Sample is introduced via direct injection or LC.
- Accurate to within 50-100 ppm for proteins
- Resolution near theoretical limit of isotopic envelopes
MALDI-TOF (generates singly or doubly charged forms of most proteins)
MALDI TOF/TOF (Bruker ultraflex III)
- Sample is mixed with matrix on a target plate and may be desalted on the target
- Accurate to within 150-300 ppm for proteins
- Resolution ¼ - ½ of the theoretical limit of isotopic envelopes
- Can be highly sensitive
- Can generate profiles from biological fluids in a single analysis
- Highly accurate for the measurement of peptides of mass < 4 kDa
ESI-MS: masses are calculated by mathematical transformation of the m/z ion series.
MALDI: Masses of the analytes are normally observed directly.
A written report is provided, describing the analysis undertaken and masses measured. Where appropriate, comparisons with calculated masses are made. Raw data are in proprietary formats and are not included with the report. Data are archived by the APC.