Different Mass spectrometry assays, different levels of sensitivity
Mass spectrometry is an analytical tool measuring the mass-to-charge ratio (m/z) of one or more molecules present in a sample. These measurements can often be used to calculate the exact molecular weight of the sample components as well. Typically, mass spectrometers can be used to identify unknown compounds via molecular weight determination, to quantify known compounds, and to determine structure and chemical properties of molecules.
How does a mass spectrometer perform such a feat? Every mass spectrometer consists of at least these three components:
Ionization Source , Mass Analyzer, Ion Detection System
Depending on the use and the type of analytes, each component might differ. Intact M-protein is often quantified by MALDI-TOF (Low resolution) while peptide is quantified by ESI-Q-Orbi (High resolution).
Intact Protein MS, MALDI-TOF
In this technique, the intact protein is analyzed on the mass spectrometer (MALDI). Inside the instrument, a laser makes it fly away from the sample to the detector. The time it takes for the protein to reach the detector will depend on its mass. However, IgG’s with similar masses might mask the presence of the M-protein. MALDI MS is often used for high thoughput. However, the low resolution of the mass spectrometer with a lack of structural information decrease the sensitivity of the method. The interference with the polyclonal background has a high negative impact on sensitivity when detecting Intact M-protein by Maldi Mass spectrometry.
Targeted MS, Clonotypic peptides MS
A targeted approach allows a much more sensitive detection and quantitation of the M-protein. The protein is initially digested into small peptides from which the primary structure of the protein is inferred via De novo sequencing. On a further step, clonotypic peptides that have a unique sequence are chosen to quantify the M-protein. Targeted MS fragmentation technology allows to distinguish the M-protein peptide from any other molecule with a similar mass since the MS fragmentation pattern generated for each peptide is sequence dependent, minimizing any possible interference.
To further improve the sensitivity, M-inSight uses an Orbitrap Mass Spectrometer that combines two mass analyzers: a quadrupole mass analyzer for high selectivity and high ion transmission and an Orbitrap mass analyzer for high dynamic range and high-resolution measurements. By combining these mass analyzers and orchestrating the coordination of ions transfer within the instrument, high performance is achieved to unlock new insights into biology and disease mechanisms.