ProMass Deconvolution fully supports data processing from all of Thermo's mass spectrometers, including the high resolution instruments such as the LTQ-FT and LTQ-Orbitrap series. However, it is important to understand the limitations of ProMass with regard to data processed from these instruments. When ProMass processes data, the deconvoluted mass peak will match the general profile of the natural isotopic width of the molecule. In order to allow for reasonable processing speed, ProMass samples the input spectrum at a resolution of 0.1 Da. For this reason, highly-resolved isotopic distributions will not be maintained in the output deconvoluted spectrum. The natural isotopic distribution (shape and width) will be maintained during the deconvolution with the reported mass closely matching the expected most abundant isotopic mass.
As an example, consider the analysis of horse myoglobin at 30,000 resolution. Large biomolecules have isotopic distributions that are several mass units wide. For the case of horse myoglobin, a monoisotopic mass of 16940.97 and a most abundant isotopic mass of 16950.99 are predicted. The FWHM (full width at half maximum) of the isotope distribution is ~8 Da. Note also, that the isotopic average mass for this molecule is 16951.5. Because the isotopic distributions of biomolecules are asymmetric gaussian, the average mass will always be slightly higher than the most abundant isotopic mass. The examples shown below utilize simulated spectra of myoblgin from the known sequence and molecular formula.
Figure 1. Simulated isotope distribution of myoglobin with exact mass of 16940.97, and most abundant isotopic mass of 16950.99.
Figure 2. The simulated electrospray ionization high-resolution mass spectrum (30,000 FWHM) of myoglobin, showing the multiply-charged ion series.
Figure 3. ProMass deconvolution of the simulated spectrum in Figure 2 . Note how the isotope peaks are not resolved in the deconvoluted spectrum, but the isotopic width closely matches the general profile shown in Figure 1. The deconvoluted peak top mass is also consistent with the predicted most abundant isotopic mass.
Conclusions